ASN RSS https://amnat.org/ Latest press releases and announcements from the ASN en-us Tue, 18 Jun 2019 05:00:00 GMT 60 “Between- and within-individual variation of maternal thyroid hormone deposition in wild great tits (<i>Parus major</i>)” https://amnat.org/an/newpapers/Oct-Hsu.html Bin-Yan Hsu, Irene Verhagen, Phillip Gienapp, Veerle M. Darras, Marcel E. Visser, and Suvi Ruuskanen (Oct 2019) Read the Article (Just Accepted)During breeding, some hormones are transferred from mothers to their offspring. These maternal hormones can influence the development, growth, physiology, and also behavior of the offspring. Evolutionary biologists have hypothesized that maternal hormones may be a “tool” for mothers to help their offspring adapt to the future environment after birth. To achieve this task, however, mothers must be able to adjust the amounts of hormone they transfer to their offspring. Can they do that? In this study, Hsu, Verhagen, Gienapp, Darras, Visser, and Ruuskanen chose the great tits (Parus major), a small passerine bird in Europe, as a model to study the flexibility of maternal hormone transfer. In birds, mothers transfer and store maternal hormones in the egg yolks. The authors analyzed the variation of maternal thyroid hormones in the eggs sampled from a Dutch population during 2013-2016. In all vertebrates, two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – are considered important to many physiological functions, such as development and metabolism. The analysis suggests that different females transfer different levels of T3 to the egg yolks on average. By contrast, each female bird is capable of adjusting T4 transfer differently for each clutch of eggs, thus potentially influencing the phenotype of the chicks and the degree of competition between the siblings hatching from these eggs. Because a previous study has shown that genetics has a moderate control over maternal T3 but not T4, this study shows that the two forms of maternal thyroid hormones exhibit different patterns of variation and flexibility, which may be linked to their respective functions. Abstract Maternal hormones are often considered a mediator of anticipatory maternal effects, namely mothers adjust maternal hormone transfer to prepare the offspring for the anticipated environment. The flexibility for mothers to adjust hormone transfer is therefore a prerequisite for such anticipatory maternal effects. Nevertheless, previous studies have only focused on the average differences of maternal hormone transfer between groups and neglected the substantial individual variation, despite that individual plasticity in maternal hormone transfer is actually the central assumption. In this study, we studied the between- and within-individual variation of maternal thyroid hormones (THs) in egg yolk of wild great tits (Parus major) and estimated the individual plasticity of maternal yolk THs across environmental temperature, clutch initiation dates and egg laying order using linear mixed-effects models. Interestingly, our models provide statistical evidence that the two main THs – the main biologically active hormone T3, and T4, which is mostly considered as a prohormone – exhibited different variation patterns. Yolk T3 showed significant between-individual variation on the average levels, in line with its previously reported moderate heritability. Yolk T4, however, showed significant between-clutch variation in the pattern over the laying sequence, suggesting a great within-individual plasticity. Our findings suggest that the role and function of the hormone within the endocrine axis likely influences its flexibility to respond to environmental change. Whether the flexibility of T4 deposition brings fitness advantage should be examined along with its potential effects on offspring, which remains to be further investigated. More forthcoming papers &raquo; <p>Bin-Yan Hsu, Irene Verhagen, Phillip Gienapp, Veerle M. Darras, Marcel E. Visser, and Suvi Ruuskanen (Oct 2019) </p><p><i><a href="https://dx.doi.org/10.1086/704738">Read the Article</a></i> (Just Accepted)</p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">D</span>uring breeding, some hormones are transferred from mothers to their offspring. These maternal hormones can influence the development, growth, physiology, and also behavior of the offspring. Evolutionary biologists have hypothesized that maternal hormones may be a “tool” for mothers to help their offspring adapt to the future environment after birth. To achieve this task, however, mothers must be able to adjust the amounts of hormone they transfer to their offspring. Can they do that?</p> <p>In this study, Hsu, Verhagen, Gienapp, Darras, Visser, and Ruuskanen chose the great tits (<i>Parus major</i>), a small passerine bird in Europe, as a model to study the flexibility of maternal hormone transfer. In birds, mothers transfer and store maternal hormones in the egg yolks. The authors analyzed the variation of maternal thyroid hormones in the eggs sampled from a Dutch population during 2013-2016. In all vertebrates, two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – are considered important to many physiological functions, such as development and metabolism. The analysis suggests that different females transfer different levels of T3 to the egg yolks on average. By contrast, each female bird is capable of adjusting T4 transfer differently for each clutch of eggs, thus potentially influencing the phenotype of the chicks and the degree of competition between the siblings hatching from these eggs. Because a previous study has shown that genetics has a moderate control over maternal T3 but not T4, this study shows that the two forms of maternal thyroid hormones exhibit different patterns of variation and flexibility, which may be linked to their respective functions.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>aternal hormones are often considered a mediator of anticipatory maternal effects, namely mothers adjust maternal hormone transfer to prepare the offspring for the anticipated environment. The flexibility for mothers to adjust hormone transfer is therefore a prerequisite for such anticipatory maternal effects. Nevertheless, previous studies have only focused on the average differences of maternal hormone transfer between groups and neglected the substantial individual variation, despite that individual plasticity in maternal hormone transfer is actually the central assumption. In this study, we studied the between- and within-individual variation of maternal thyroid hormones (THs) in egg yolk of wild great tits (<i>Parus major</i>) and estimated the individual plasticity of maternal yolk THs across environmental temperature, clutch initiation dates and egg laying order using linear mixed-effects models. Interestingly, our models provide statistical evidence that the two main THs – the main biologically active hormone T3, and T4, which is mostly considered as a prohormone – exhibited different variation patterns. Yolk T3 showed significant between-individual variation on the average levels, in line with its previously reported moderate heritability. Yolk T4, however, showed significant between-clutch variation in the pattern over the laying sequence, suggesting a great within-individual plasticity. Our findings suggest that the role and function of the hormone within the endocrine axis likely influences its flexibility to respond to environmental change. Whether the flexibility of T4 deposition brings fitness advantage should be examined along with its potential effects on offspring, which remains to be further investigated. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Jun 2019 05:00:00 GMT “What determines the distinct morphology of species with a particular ecology? The roles of many-to-one mapping and trade-offs in the evolution of frog ecomorphology and performance” https://amnat.org/an/newpapers/Oct-Moen.html Daniel S. Moen (Oct 2019)Read the Article (Just Accepted) Many-to-one mapping leads to specialized ecomorphs without compromising performance in a shared behavior Ecologists and evolutionary biologists have long recognized that species that share a similar ecology (e.g. habitat use, diet) have similar body forms, or morphology. Yet the reasons why some body forms are related to ecology are often complicated by the fact that some organisms have many different behaviors associated with their ecology. For example, if an animal that lives mostly in the water has large leg muscles, it may have such muscles because those larger muscles help those species swim better than species that do not regularly swim. But such species may also move terrestrially (e.g. running or jumping), and it may be unclear whether the big muscles will aid or inhibit the terrestrial movement. A new article in The&nbsp;American Naturalist by Daniel Moen explores why certain frog body forms are associated with the microhabitats those species use by linking ecology, morphology, and functional performance. He looked at frogs and toads from three different continents and compared microhabitat (e.g. living in trees or water), leg morphology (leg length and muscle mass), and performance in two different behaviors (jumping and swimming). The results showed that frogs in different microhabitats were different in their leg morphology, and some of those differences were mirrored by swimming ability. However, all species – regardless of microhabitat – jumped equally well, as might be expected for organisms like frogs that use jumping as their primary terrestrial locomotion. The similar jumping ability despite differences in swimming ability and body form can be explained by a concept called many-to-one mapping, in which multiple anatomical traits affect functional performance, allowing species to specialize in body form for some behaviors but maintain similar performance in others. More generally, the study emphasizes the use of evolutionary analyses at large scales (temporally and geographically) for understanding the evolution of body form and its fit to ecology. Abstract Organisms inhabiting a specific environment often have distinct morphology, but the factors that affect this fit are unclear when multiple morphological traits affect performance in multiple behaviors. Does the realized morphology of a species reflect a compromise in performance among behaviors (i.e. trade-offs)? Or does many-to-one mapping result in morphological distinctness without compromising performance across behaviors? The importance of these principles in organismal design has rarely been compared at the macroevolutionary scale. Here, I study 191 species of frogs around the world that inhabit different microhabitats, using models of phenotypic evolution to examine how form-function relationships may explain the fit between ecology and morphology. I found three key results. First, despite being distinct in leg morphology, ecomorphs were similar in jumping performance. Second, ecomorphs that regularly swim showed higher swimming performance, which paralleled the higher leg muscle mass in these taxa. Third, many-to-one mapping of form onto function occurred at all but the highest levels of both jumping and swimming performance. The seemingly contradictory first two results were explained by the third: when one behavior occurs in all species while another is restricted to a subset, many-to-one mapping allows species with distinct ecologies to have distinct body forms that reflect their specialized behavior while maintaining similar performance in a more general, shared behavior. More forthcoming papers &raquo; <p>Daniel S. Moen (Oct 2019)</p><p><i><a href="https://dx.doi.org/10.1086/704736">Read the Article</a></i> (Just Accepted)</p> <p><b>Many-to-one mapping leads to specialized ecomorphs without compromising performance in a shared behavior </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">E</span>cologists and evolutionary biologists have long recognized that species that share a similar ecology (e.g. habitat use, diet) have similar body forms, or morphology. Yet the reasons why some body forms are related to ecology are often complicated by the fact that some organisms have many different behaviors associated with their ecology. For example, if an animal that lives mostly in the water has large leg muscles, it may have such muscles because those larger muscles help those species swim better than species that do not regularly swim. But such species may also move terrestrially (e.g. running or jumping), and it may be unclear whether the big muscles will aid or inhibit the terrestrial movement. A new article in <i>The&nbsp;American Naturalist</i> by Daniel Moen explores why certain frog body forms are associated with the microhabitats those species use by linking ecology, morphology, and functional performance. He looked at frogs and toads from three different continents and compared microhabitat (e.g. living in trees or water), leg morphology (leg length and muscle mass), and performance in two different behaviors (jumping and swimming). The results showed that frogs in different microhabitats were different in their leg morphology, and some of those differences were mirrored by swimming ability. However, all species – regardless of microhabitat – jumped equally well, as might be expected for organisms like frogs that use jumping as their primary terrestrial locomotion. The similar jumping ability despite differences in swimming ability and body form can be explained by a concept called many-to-one mapping, in which multiple anatomical traits affect functional performance, allowing species to specialize in body form for some behaviors but maintain similar performance in others. More generally, the study emphasizes the use of evolutionary analyses at large scales (temporally and geographically) for understanding the evolution of body form and its fit to ecology.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">O</span>rganisms inhabiting a specific environment often have distinct morphology, but the factors that affect this fit are unclear when multiple morphological traits affect performance in multiple behaviors. Does the realized morphology of a species reflect a compromise in performance among behaviors (i.e. trade-offs)? Or does many-to-one mapping result in morphological distinctness without compromising performance across behaviors? The importance of these principles in organismal design has rarely been compared at the macroevolutionary scale. Here, I study 191 species of frogs around the world that inhabit different microhabitats, using models of phenotypic evolution to examine how form-function relationships may explain the fit between ecology and morphology. I found three key results. First, despite being distinct in leg morphology, ecomorphs were similar in jumping performance. Second, ecomorphs that regularly swim showed higher swimming performance, which paralleled the higher leg muscle mass in these taxa. Third, many-to-one mapping of form onto function occurred at all but the highest levels of both jumping and swimming performance. The seemingly contradictory first two results were explained by the third: when one behavior occurs in all species while another is restricted to a subset, many-to-one mapping allows species with distinct ecologies to have distinct body forms that reflect their specialized behavior while maintaining similar performance in a more general, shared behavior. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 11 Jun 2019 05:00:00 GMT “Early sibling conflict may ultimately benefit the family” https://amnat.org/an/newpapers/Oct-Smith.html Alyssa Laney Smith, Daniel Z. Atwater, and Ragan M. Callaway (Oct 2019) Read the Article (Just Accepted) Early sibling conflict via kin recognition may ultimately benefit the family for an invasive grass Seeds of goatgrass, a European plant that is invading California, have the ability to chemically inhibit the germination of their siblings more than non-siblings. At face value, this seems like strong conflict among relatives. However, in experiments with no chemical suppression of germination, goatgrass seedlings even more strongly suppressed their siblings through competition. Thus, by suppressing germination, goatgrass may allow their close kin to remain dormant for a time, and by doing so to avoid competition within the family later in life. Abstract Relatives often interact differently with each other than with non-relatives, and whether kin cooperate or compete has important consequences for the evolution of mating systems, seed size, dispersal, and competition. Previous research found that the larger of the size-dimorphic seeds produced by the annual plant, Aegilops triuncialis, suppressed germination of their smaller sibs by 25-60%. Here, we found evidence for kin-recognition and sibling rivalry later in life among Aegilops seedlings that places seed-seed interactions in a broader context. In experiments with size-dimorphic seeds, seedlings reduced the growth of sibling seedlings by ~40% but that of non-sibling seedlings by ~25%. These sequential antagonistic interactions between seeds and then seedlings provide insight into conflict and cooperation among kin. Kin-based conflict among seeds may maintain dormancy for some seeds until the coast is clear of more competitive siblings. If so, biotically induced seed dormancy may be a unique form of cooperation, which increases the inclusive fitness of maternal plants and offspring by minimizing competition among kin. More forthcoming papers &raquo; <p>Alyssa Laney Smith, Daniel Z. Atwater, and Ragan M. Callaway (Oct 2019) </p> <p><i><a href="https://dx.doi.org/10.1086/704773">Read the Article</a></i> (Just Accepted)</p> <p><b>Early sibling conflict via kin recognition may ultimately benefit the family for an invasive grass </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>eeds of goatgrass, a European plant that is invading California, have the ability to chemically inhibit the germination of their siblings more than non-siblings. At face value, this seems like strong conflict among relatives. However, in experiments with no chemical suppression of germination, goatgrass seedlings even more strongly suppressed their siblings through competition. Thus, by suppressing germination, goatgrass may allow their close kin to remain dormant for a time, and by doing so to avoid competition within the family later in life.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">R</span>elatives often interact differently with each other than with non-relatives, and whether kin cooperate or compete has important consequences for the evolution of mating systems, seed size, dispersal, and competition. Previous research found that the larger of the size-dimorphic seeds produced by the annual plant, <i>Aegilops triuncialis</i>, suppressed germination of their smaller sibs by 25-60%. Here, we found evidence for kin-recognition and sibling rivalry later in life among <i>Aegilops</i> seedlings that places seed-seed interactions in a broader context. In experiments with size-dimorphic seeds, seedlings reduced the growth of sibling seedlings by ~40% but that of non-sibling seedlings by ~25%. These sequential antagonistic interactions between seeds and then seedlings provide insight into conflict and cooperation among kin. Kin-based conflict among seeds may maintain dormancy for some seeds until the coast is clear of more competitive siblings. If so, biotically induced seed dormancy may be a unique form of cooperation, which increases the inclusive fitness of maternal plants and offspring by minimizing competition among kin. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 11 Jun 2019 05:00:00 GMT “Maladapted prey subsidize predators and facilitate range expansion” https://amnat.org/an/newpapers/Oct-Urban.html Mark C. Urban, Alice Scarpa, Justin M. J. Travis, and Greta Bocedi (Special Feature on Maladaptation)Read the Article (Just Accepted)Life is good when dinner is quick and easy. But prey usually make dinner difficult for predators by evolving defenses like thorns, shells, camouflage, and poison. Yet prey sometimes evolve to be less defended where predators are rare, like at the edge of a predator’s range. In these situations, prey are likely to become adapted to low-predator conditions, and maladapted to predators. How do these maladapted prey affect the predators that eat them? Scientists from the University of Connecticut and University of Aberdeen set out to answer this question using a combination of classic analytical theory and supercomputer-sized simulations. By providing a subsidy of easily captured resources, the authors find that maladapted prey can enhance predator abundances, persistence, and geographic range size. Simply put, maladaptation makes dinner easy for predators. Maladapted prey become even more important when predators are expanding their range, such as during climate change. As predators expand, they encounter less and less defended prey, speeding up the predator’s range expansion. These maladapted prey can even prevent the predator’s extinction during environmental change. These effects can be generalized to any enemy and victim system, ranging from plants and their herbivores to humans and our diseases. Overall, the work suggests the need to understand not just the adaptive dynamics of predator and prey, but their maladaptive dynamics as well. More generally, we need to work to spend more time considering how both adaptation and maladaptation affect species interactions to get a more complete view of biodiversity patterns, limits to species ranges, and responses to environmental change. Abstract Dispersal of prey from predator-free patches frequently supplies a trophic subsidy to predators by providing more prey than are produced locally. Prey arriving from predator-free patches might also have evolved weaker defenses against predators and thus enhance trophic subsidies by providing easily captured prey. Using local models assuming a linear or accelerating tradeoff between defense and population growth rate, we demonstrate that immigration of undefended prey increased predator abundances and decreased defended prey through eco-evolutionary apparent competition. In individual-based models with spatial structure, explicit genetics, and gene flow along an environmental gradient, prey became maladapted to predators at the predator’s range edge, and greater gene flow enhanced this maladaptation. The predator gained a subsidy from these easily captured prey, which enhanced its abundance, facilitated it's persistence in marginal habitats, extended its range extent, and enhanced range shifts during environmental changes, such as climate change. Once the predator expanded, prey adapted to it, and the advantage disappeared, resulting in an elastic predator range margin driven by eco-evolutionary dynamics. Overall, the results indicate a need to consider gene flow-induced maladaptation and species interactions as mutual forces that frequently determine ecological and evolutionary dynamics and patterns in nature. More forthcoming papers &raquo; <p>Mark C. Urban, Alice Scarpa, Justin M. J. Travis, and Greta Bocedi (Special Feature on Maladaptation)</p><p><i><a href="https://dx.doi.org/10.1086/704780">Read the Article</a></i> (Just Accepted)</p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>ife is good when dinner is quick and easy. But prey usually make dinner difficult for predators by evolving defenses like thorns, shells, camouflage, and poison. Yet prey sometimes evolve to be less defended where predators are rare, like at the edge of a predator’s range. In these situations, prey are likely to become adapted to low-predator conditions, and maladapted to predators. How do these maladapted prey affect the predators that eat them? </p><p>Scientists from the University of Connecticut and University of Aberdeen set out to answer this question using a combination of classic analytical theory and supercomputer-sized simulations. By providing a subsidy of easily captured resources, the authors find that maladapted prey can enhance predator abundances, persistence, and geographic range size. Simply put, maladaptation makes dinner easy for predators. </p><p>Maladapted prey become even more important when predators are expanding their range, such as during climate change. As predators expand, they encounter less and less defended prey, speeding up the predator’s range expansion. These maladapted prey can even prevent the predator’s extinction during environmental change. These effects can be generalized to any enemy and victim system, ranging from plants and their herbivores to humans and our diseases. </p><p>Overall, the work suggests the need to understand not just the adaptive dynamics of predator and prey, but their maladaptive dynamics as well. More generally, we need to work to spend more time considering how both adaptation and maladaptation affect species interactions to get a more complete view of biodiversity patterns, limits to species ranges, and responses to environmental change. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">D</span>ispersal of prey from predator-free patches frequently supplies a trophic subsidy to predators by providing more prey than are produced locally. Prey arriving from predator-free patches might also have evolved weaker defenses against predators and thus enhance trophic subsidies by providing easily captured prey. Using local models assuming a linear or accelerating tradeoff between defense and population growth rate, we demonstrate that immigration of undefended prey increased predator abundances and decreased defended prey through eco-evolutionary apparent competition. In individual-based models with spatial structure, explicit genetics, and gene flow along an environmental gradient, prey became maladapted to predators at the predator’s range edge, and greater gene flow enhanced this maladaptation. The predator gained a subsidy from these easily captured prey, which enhanced its abundance, facilitated it's persistence in marginal habitats, extended its range extent, and enhanced range shifts during environmental changes, such as climate change. Once the predator expanded, prey adapted to it, and the advantage disappeared, resulting in an elastic predator range margin driven by eco-evolutionary dynamics. Overall, the results indicate a need to consider gene flow-induced maladaptation and species interactions as mutual forces that frequently determine ecological and evolutionary dynamics and patterns in nature. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 11 Jun 2019 05:00:00 GMT “(In)exhaustible suppliers for evolution? Epistatic selection tunes the adaptive potential of non-genetic inheritance” https://amnat.org/an/newpapers/Oct-Rajon-A.html Etienne Rajon and Sylvain Charlat (Oct 2019) Read the Article (Just Accepted) Think non-genetic inheritance is important due to massive (epi)mutation rates? Not necessarily!Abstract Non-genetic inheritance media, from methyl-accepting cytosines to culture, tend to ‘mutate’ more frequently than DNA sequences. Whether or not this makes them inexhaustible suppliers for adaptive evolution will depend on the effect of non-genetic mutations (hereafter epimutations) on fitness-related traits. Here we investigate how these effects might themselves evolve, specifically whether natural selection may set boundaries to the adaptive potential of non-genetic inheritance media due to their higher mutability. In our model, the genetic and epigenetic contributions to a non-neutral phenotype are controlled by an epistatic modifier locus, which evolves under the combined effects of drift and selection. We show that a pure genetic control evolves when the environment is stable, provided that the population is large, such that the phenotype becomes robust to frequent epimutations. When the environment fluctuates, however, selection on the modifier locus also fluctuates and can overall produce a large non-genetic contribution to the phenotype, especially when the epimutation rate matches the rate of environmental variation. We further show that selection on the modifier locus is generally insensitive to recombination, meaning it is mostly direct, i.e. not relying on subsequent effects in future generations. These results suggest that unstable inheritance media might significantly contribute to fitness variation of traits subject to highly variable selective pressures, but little to traits responding to scarcely variable aspects of the environment. More generally, our study demonstrates that the rate of mutation and the adaptive potential of any inheritance media should not be seen as independent properties. Une source (in)tarissable pour l’évolution&nbsp;? Comment le potentiel adaptatif de l’hérédité non-génétique est modulé par la sélection épistatique Les supports de l’hérédité non-génétique, des cytosines méthylables à la culture, ont tendance à «&nbsp;muter&nbsp;» plus fréquemment que les séquences d’ADN. Ces supports ne peuvent néanmoins représenter une source intarissable de variation que si l’effet de ces mutations non-génétiques (ou épimutations) sur des traits liés à la fitness demeure élevé. Dans le cadre de ce projet, nous étudions comment ces effets peuvent évoluer, en particulier si la sélection naturelle peut limiter le potentiel adaptatif des épimutations du fait de leur forte mutabilité. Dans notre modèle, les contributions des supports génétiques et non-génétiques sont contrôlées par un locus «&nbsp;modificateur&nbsp;» agissant de manière épistatique, dont l’évolution dépend de l’action conjointe de la dérive et de la sélection. Nos résultats montrent qu’une forte contribution génétique devrait évoluer dans un environnement stable et pour une taille de population élevée, si bien qu’on peut s’attendre à ce que le phénotype dans ce contexte soit robuste aux épimutations. En revanche, lorsque l’environnement fluctue, la sélection sur le locus modificateur peut aussi fluctuer et aboutir à une contribution élevée du support non-génétique, en particulier lorsque le taux d’épimutation correspond au taux de changement environnemental. De plus, nous montrons que la sélection sur le locus modificateur est en général indépendante du taux de recombinaison, indiquant que cette sélection est directe et ne dépend pas des effets à venir dans les générations futures. Nos résultats indiquent que les supports instables de l’hérédité peuvent contribuer de façon importante à des variations de traits soumis à des pressions de sélection variables, mais peu à des traits liés à des caractéristiques de l’environnement stables dans le temps. De façon plus large, cette étude démontre que le taux d’occurrence et l’effet des mutations ne peuvent pas être considérés comme des propriétés indépendantes. More forthcoming papers &raquo; <p>Etienne Rajon and Sylvain Charlat (Oct 2019) </p><p><i><a href="https://dx.doi.org/10.1086/704772">Read the Article</a></i> (Just Accepted)</p> <p><b>Think non-genetic inheritance is important due to massive (epi)mutation rates? Not necessarily!</b></p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">N</span>on-genetic inheritance media, from methyl-accepting cytosines to culture, tend to ‘mutate’ more frequently than DNA sequences. Whether or not this makes them inexhaustible suppliers for adaptive evolution will depend on the effect of non-genetic mutations (hereafter epimutations) on fitness-related traits. Here we investigate how these effects might themselves evolve, specifically whether natural selection may set boundaries to the adaptive potential of non-genetic inheritance media due to their higher mutability. In our model, the genetic and epigenetic contributions to a non-neutral phenotype are controlled by an epistatic modifier locus, which evolves under the combined effects of drift and selection. We show that a pure genetic control evolves when the environment is stable, provided that the population is large, such that the phenotype becomes robust to frequent epimutations. When the environment fluctuates, however, selection on the modifier locus also fluctuates and can overall produce a large non-genetic contribution to the phenotype, especially when the epimutation rate matches the rate of environmental variation. We further show that selection on the modifier locus is generally insensitive to recombination, meaning it is mostly direct, i.e. not relying on subsequent effects in future generations. These results suggest that unstable inheritance media might significantly contribute to fitness variation of traits subject to highly variable selective pressures, but little to traits responding to scarcely variable aspects of the environment. More generally, our study demonstrates that the rate of mutation and the adaptive potential of any inheritance media should not be seen as independent properties. </p> <h4>Une source (in)tarissable pour l’évolution&nbsp;? Comment le potentiel adaptatif de l’hérédité non-génétique est modulé par la sélection épistatique</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>es supports de l’hérédité non-génétique, des cytosines méthylables à la culture, ont tendance à «&nbsp;muter&nbsp;» plus fréquemment que les séquences d’ADN. Ces supports ne peuvent néanmoins représenter une source intarissable de variation que si l’effet de ces mutations non-génétiques (ou épimutations) sur des traits liés à la fitness demeure élevé. Dans le cadre de ce projet, nous étudions comment ces effets peuvent évoluer, en particulier si la sélection naturelle peut limiter le potentiel adaptatif des épimutations du fait de leur forte mutabilité. Dans notre modèle, les contributions des supports génétiques et non-génétiques sont contrôlées par un locus «&nbsp;modificateur&nbsp;» agissant de manière épistatique, dont l’évolution dépend de l’action conjointe de la dérive et de la sélection. Nos résultats montrent qu’une forte contribution génétique devrait évoluer dans un environnement stable et pour une taille de population élevée, si bien qu’on peut s’attendre à ce que le phénotype dans ce contexte soit robuste aux épimutations. En revanche, lorsque l’environnement fluctue, la sélection sur le locus modificateur peut aussi fluctuer et aboutir à une contribution élevée du support non-génétique, en particulier lorsque le taux d’épimutation correspond au taux de changement environnemental. De plus, nous montrons que la sélection sur le locus modificateur est en général indépendante du taux de recombinaison, indiquant que cette sélection est directe et ne dépend pas des effets à venir dans les générations futures. Nos résultats indiquent que les supports instables de l’hérédité peuvent contribuer de façon importante à des variations de traits soumis à des pressions de sélection variables, mais peu à des traits liés à des caractéristiques de l’environnement stables dans le temps. De façon plus large, cette étude démontre que le taux d’occurrence et l’effet des mutations ne peuvent pas être considérés comme des propriétés indépendantes. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 11 Jun 2019 05:00:00 GMT “Interspecific covariation in courtship displays, iridescent plumage, solar orientation, and their interactions in hummingbirds” https://amnat.org/an/newpapers/Oct-Simpson.html Richard K. Simpson and Kevin J. McGraw (Oct 2019) Read the Article (Just Accepted) The complex evolution of hummingbird visual courtship signals produced varied and unique signal interaction properties Animals exhibit a staggering array of exaggerated ornaments, such as peacock tails or deer antlers, and complex behavioral displays, like the elaborate dances of birds of paradise. Ornaments and behaviors are often used for courtship, and many animals use both ornaments and behaviors simultaneously, which prompts the questions of 1) why there is such a diversity of signaling traits, and 2) why animals use multiple signaling traits together. Previous work addressing these two questions has focused on understanding the information conveyed through animal signals, and how signals are transmitted and detected through the environment. However, Drs. Simpson and McGraw set out to tackle these questions from a different angle. Previously they found that male hummingbirds can alter the presentation of their iridescent throat feathers during courtship dances and that this signal interaction changes how males appear to females. For example, when a male is dancing for a female, he can manipulate how he orients his feathers relative to the female and sun to create a flashy, strobe-like color appearance. To tackle questions about signal evolution and diversity, Simpson and McGraw tested how signal interactions vary among multiple hummingbird species, and how signal interactions may be co-evolving with other signaling traits. They quantified the courtship dances, iridescent feathers, and signal interactions (male color appearance during courtship) of six hummingbird species in the American Southwest and found that signal interactions do vary among species, with some having very flashy color appearances during courtship and others having very consistently colored but brighter color appearances. Further, they found that species with more complex dances have flashier color appearances, while species with larger and more colorful feathers have brighter, more consistent color appearances, illustrating how these different signaling traits can co-evolve. This work demonstrates the need to incorporate signal interactions into future research on multiple signals so that biologists can better and more deeply understand the evolution and diversity of animal signals. Abstract Many animals communicate using multiple signals. Historically, most attention was paid to how these traits evolve and function in isolation, but recent work has focused on how signals may interact with one another and produce unique signal interaction properties. These interaction properties vary within species, but little is known about how they vary among species, especially with regards to how the expression of particular signals may drive different signal interaction mechanisms. We studied the evolutionary relationships between iridescent plumage, courtship (shuttle) displays, solar environment, and male color appearance during a display (i.e. the signal interaction property) among six species of North American “bee” hummingbirds. We found that color appearances co-vary with behavioral and plumage properties, which themselves negatively co-vary, such that species with more exaggerated displays appeared flashier during courtship, while species with more exaggerated plumage appeared brighter/more colorful with minimal color-changes. By understanding how signal interaction properties co-vary with signals, we were able to discover the complex, multi-layered evolutionary relationships underlying these traits and uncover new potential drivers of signal evolution. Our results highlight how studying the interaction properties between animal signals provides a richer understanding of how those traits evolved and diversified. More forthcoming papers &raquo; <p>Richard K. Simpson and Kevin J. McGraw (Oct 2019) </p><p><i><a href="https://dx.doi.org/10.1086/704774">Read the Article</a></i> (Just Accepted) </p> <p><b>The complex evolution of hummingbird visual courtship signals produced varied and unique signal interaction properties </b></p><p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">A</span>nimals exhibit a staggering array of exaggerated ornaments, such as peacock tails or deer antlers, and complex behavioral displays, like the elaborate dances of birds of paradise. Ornaments and behaviors are often used for courtship, and many animals use both ornaments and behaviors simultaneously, which prompts the questions of 1) why there is such a diversity of signaling traits, and 2) why animals use multiple signaling traits together. Previous work addressing these two questions has focused on understanding the information conveyed through animal signals, and how signals are transmitted and detected through the environment. However, Drs. Simpson and McGraw set out to tackle these questions from a different angle. Previously they found that male hummingbirds can alter the presentation of their iridescent throat feathers during courtship dances and that this signal interaction changes how males appear to females. For example, when a male is dancing for a female, he can manipulate how he orients his feathers relative to the female and sun to create a flashy, strobe-like color appearance. To tackle questions about signal evolution and diversity, Simpson and McGraw tested how signal interactions vary among multiple hummingbird species, and how signal interactions may be co-evolving with other signaling traits. They quantified the courtship dances, iridescent feathers, and signal interactions (male color appearance during courtship) of six hummingbird species in the American Southwest and found that signal interactions do vary among species, with some having very flashy color appearances during courtship and others having very consistently colored but brighter color appearances. Further, they found that species with more complex dances have flashier color appearances, while species with larger and more colorful feathers have brighter, more consistent color appearances, illustrating how these different signaling traits can co-evolve. This work demonstrates the need to incorporate signal interactions into future research on multiple signals so that biologists can better and more deeply understand the evolution and diversity of animal signals.</p> <hr /><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">M</span>any animals communicate using multiple signals. Historically, most attention was paid to how these traits evolve and function in isolation, but recent work has focused on how signals may interact with one another and produce unique signal interaction properties. These interaction properties vary within species, but little is known about how they vary among species, especially with regards to how the expression of particular signals may drive different signal interaction mechanisms. We studied the evolutionary relationships between iridescent plumage, courtship (shuttle) displays, solar environment, and male color appearance during a display (i.e. the signal interaction property) among six species of North American &ldquo;bee&rdquo; hummingbirds. We found that color appearances co-vary with behavioral and plumage properties, which themselves negatively co-vary, such that species with more exaggerated displays appeared flashier during courtship, while species with more exaggerated plumage appeared brighter/more colorful with minimal color-changes. By understanding how signal interaction properties co-vary with signals, we were able to discover the complex, multi-layered evolutionary relationships underlying these traits and uncover new potential drivers of signal evolution. Our results highlight how studying the interaction properties between animal signals provides a richer understanding of how those traits evolved and diversified.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 11 Jun 2019 05:00:00 GMT “Soil microbiomes underlie population persistence of an endangered plant species” https://amnat.org/an/newpapers/Oct-David.html Read the Article (Just Accepted) Bioassays, long-term demographic data, and integral projection modeling show soil microbiomes boost plant populationsMicrobiomes can have profound effects on their hosts, yet we are still learning about their effects on higher-order processes. While recent research has considered how microbiomes alter processes at the community and ecosystem levels, lost in the shuffle has been the microbiome’s effect on host species’ populations, a knowledge gap that could have serious implications for plant and animal species listed as threatened and endangered. The origins of this study began 25 years ago with the first censuses of the endangered Hypericum cumulicola, a perennial herb endemic to the imperiled Florida scrub ecosystem. Using detailed demographic data collected annually from 15 populations at Archbold Biological Station, along with spatial and historical factors such as fire history, elevation, patch aggregation, and patch size, an integral projection model (IPM) was developed that quantified H.&nbsp;cumulicola population dynamics across the landscape (Quintana-Ascencio et al. 2018 Journal of Ecology). Because of the flexibility built into this original population model, it would serve as an ideal tool to quantify how other factors, namely the soil microbiome, could influence population growth of the plant, provided that the effects of the soil microbiome on individual plants could be quantified. In this new study, the authors set out to do just that by conducting bioassays that quantified the effect of microbes on two demographic rates critical to H.&nbsp;cumulicola populations – seed germination and first-year growth. By comparing the effects of live and sterilized soils on these demographic rates, they found that microbes substantially increased seed germination rates. Next, the authors incorporated the results of these bioassays into the IPM to quantify the population-level effects of the soil microbiome. The results were striking – in the absence of a soil microbiome, H.&nbsp;cumulicola populations would rarely experience population growth, leading to the conclusion that the soil microbiome plays a critical role in maintaining population persistence of its endangered host. Abstract Microbiomes can dramatically alter individual plant performance, yet how these effects influence higher order processes is not well resolved. In particular, little is known about how microbiome effects on individual plants alter plant population dynamics, a question critical to imperiled species conservation. Here, we integrate bioassays, multidecadal demographic data, and integral projection modeling to determine how the presence of the natural soil microbiome underlies plant population dynamics. Simulations indicated that the presence of soil microbiomes boosted population growth rates (&lambda;) of the endangered Hypericum cumulicola by 13% on average, the difference between population growth versus decline in 76% of patches. The greatest benefit (47% increase in &lambda;) occurred in low nutrient, high elevation habitats, suggesting that the soil microbiome may help expand H.&nbsp;cumulicola’s distribution to include these stressful habitats. Our results demonstrate that soil microbiomes can significantly affect plant population growth and persistence, and support the incorporation of soil microbiomes into conservation planning. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704684">Read the Article</a></i> (Just Accepted) </p> <p><b>Bioassays, long-term demographic data, and integral projection modeling show soil microbiomes boost plant populations</b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>icrobiomes can have profound effects on their hosts, yet we are still learning about their effects on higher-order processes. While recent research has considered how microbiomes alter processes at the community and ecosystem levels, lost in the shuffle has been the microbiome’s effect on host species’ <i>populations</i>, a knowledge gap that could have serious implications for plant and animal species listed as threatened and endangered. </p><p>The origins of this study began 25 years ago with the first censuses of the endangered <i>Hypericum cumulicola</i>, a perennial herb endemic to the imperiled Florida scrub ecosystem. Using detailed demographic data collected annually from 15 populations at Archbold Biological Station, along with spatial and historical factors such as fire history, elevation, patch aggregation, and patch size, an integral projection model (IPM) was developed that quantified <i>H.&nbsp;cumulicola</i> population dynamics across the landscape (Quintana-Ascencio et al. 2018 <i>Journal of Ecology</i>). Because of the flexibility built into this original population model, it would serve as an ideal tool to quantify how other factors, namely the soil microbiome, could influence population growth of the plant, provided that the effects of the soil microbiome on individual plants could be quantified. </p><p>In this new study, the authors set out to do just that by conducting bioassays that quantified the effect of microbes on two demographic rates critical to <i>H.&nbsp;cumulicola</i> populations – seed germination and first-year growth. By comparing the effects of live and sterilized soils on these demographic rates, they found that microbes substantially increased seed germination rates. Next, the authors incorporated the results of these bioassays into the IPM to quantify the population-level effects of the soil microbiome. The results were striking – in the absence of a soil microbiome, <i>H.&nbsp;cumulicola</i> populations would rarely experience population growth, leading to the conclusion that the soil microbiome plays a critical role in maintaining population persistence of its endangered host. </p> <hr /><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">M</span>icrobiomes can dramatically alter individual plant performance, yet how these effects influence higher order processes is not well resolved. In particular, little is known about how microbiome effects on individual plants alter plant population dynamics, a question critical to imperiled species conservation. Here, we integrate bioassays, multidecadal demographic data, and integral projection modeling to determine how the presence of the natural soil microbiome underlies plant population dynamics. Simulations indicated that the presence of soil microbiomes boosted population growth rates (&lambda;) of the endangered <i>Hypericum cumulicola</i> by 13% on average, the difference between population growth versus decline in 76% of patches. The greatest benefit (47% increase in &lambda;) occurred in low nutrient, high elevation habitats, suggesting that the soil microbiome may help expand <i>H.&nbsp;cumulicola</i>&rsquo;s distribution to include these stressful habitats. Our results demonstrate that soil microbiomes can significantly affect plant population growth and persistence, and support the incorporation of soil microbiomes into conservation planning.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 06 Jun 2019 05:00:00 GMT “Pulsed immigration events can facilitate adaptation to harsh sink environments” https://amnat.org/an/newpapers/Sep-Peniston.html Read the Article (Just Accepted) The temporal spacing of immigration events can facilitate niche evolution in harsh sink environments The movement rate of organisms can vary a lot from year to year. For instance, more butterflies disperse among habitats in warmer years than colder ones, and the dispersal of many marine organisms depends on ocean conditions. Most ecological and evolutionary studies ignore this variation and assume that organisms have constant movement rates between habitats. However, in a recent paper, researchers at the University of Florida have shown that variation in dispersal rates may be important to understanding how species adapt to new environments. The researchers built mathematical models in which individuals of a species immigrated into a new environment to which the species was poorly adapted. They then evaluated how well the species could adapt to this environment. In different versions of the model, immigration could either happen every year or there could be years without immigration. They showed that adaptation to new environments was more likely when there were longer stretches of time between immigration events. This is because when maladapted immigrants mate with better adapted residents in the new environment, their genes get mixed together in their offspring. Therefore, any local adaptation that does occur may be lost when new immigrants arrive and mate. Longer gaps between immigration events allow the population to become better adapted before the next immigration event. Once the population becomes well-adapted, the population size will increase, and the relatively small number of new immigrants will no longer have a major effect on local adaptation. By investigating more realistic patterns of dispersal, this study offers new insights into how populations adapt to new environments. With increasing globalization, climate change, and habitat fragmentation, variation in migration rates between habitats are likely to change for many species. Therefore, the results of this study may have important implications for understanding how organisms will respond to the large-scale impacts humans are inflicting on our planet. Abstract In nature, rates of dispersal vary greatly over time, yet most theoretical explorations of ecological and evolutionary dynamics to date have assumed constant movement rates. Here, we examine how a particular pattern of temporal variation—periodic pulses of immigration—influences adaptation to a harsh environment, in which a species experiences conditions outside its niche requirements. Using both deterministic models and stochastic individual-based simulations, we show that for many ecological and genetic scenarios, temporally spacing out immigration events increases the probability that local adaptation is sufficient for persistence (i.e., niche evolution). When immigration events are too frequent, gene flow can hamper local adaptation in sexual species, but sufficiently infrequent pulses of immigration allow for repeated opportunities for adaptation with temporary escapes from gene flow during which local selection is unleashed. We develop versions of our models with and without density dependence for three different assumptions about the genetics underlying fitness (haploid, diploid, and quantitative genetic variation) so that our results may be applicable to a wide range of natural systems. Our study adds to a growing body of literature showing that temporal variation in migration rates can have significant effects on local adaptation, and is among the first to show how such variation affects niche evolution. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704608">Read the Article</a></i> (Just Accepted)</p> <p><b>The temporal spacing of immigration events can facilitate niche evolution in harsh sink environments </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he movement rate of organisms can vary a lot from year to year. For instance, more butterflies disperse among habitats in warmer years than colder ones, and the dispersal of many marine organisms depends on ocean conditions. Most ecological and evolutionary studies ignore this variation and assume that organisms have constant movement rates between habitats. However, in a recent paper, researchers at the University of Florida have shown that variation in dispersal rates may be important to understanding how species adapt to new environments.</p> <p>The researchers built mathematical models in which individuals of a species immigrated into a new environment to which the species was poorly adapted. They then evaluated how well the species could adapt to this environment. In different versions of the model, immigration could either happen every year or there could be years without immigration. They showed that adaptation to new environments was more likely when there were longer stretches of time between immigration events. This is because when maladapted immigrants mate with better adapted residents in the new environment, their genes get mixed together in their offspring. Therefore, any local adaptation that does occur may be lost when new immigrants arrive and mate. Longer gaps between immigration events allow the population to become better adapted before the next immigration event. Once the population becomes well-adapted, the population size will increase, and the relatively small number of new immigrants will no longer have a major effect on local adaptation.</p> <p>By investigating more realistic patterns of dispersal, this study offers new insights into how populations adapt to new environments. With increasing globalization, climate change, and habitat fragmentation, variation in migration rates between habitats are likely to change for many species. Therefore, the results of this study may have important implications for understanding how organisms will respond to the large-scale impacts humans are inflicting on our planet.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n nature, rates of dispersal vary greatly over time, yet most theoretical explorations of ecological and evolutionary dynamics to date have assumed constant movement rates. Here, we examine how a particular pattern of temporal variation—periodic pulses of immigration—influences adaptation to a harsh environment, in which a species experiences conditions outside its niche requirements. Using both deterministic models and stochastic individual-based simulations, we show that for many ecological and genetic scenarios, temporally spacing out immigration events increases the probability that local adaptation is sufficient for persistence (i.e., niche evolution). When immigration events are too frequent, gene flow can hamper local adaptation in sexual species, but sufficiently infrequent pulses of immigration allow for repeated opportunities for adaptation with temporary escapes from gene flow during which local selection is unleashed. We develop versions of our models with and without density dependence for three different assumptions about the genetics underlying fitness (haploid, diploid, and quantitative genetic variation) so that our results may be applicable to a wide range of natural systems. Our study adds to a growing body of literature showing that temporal variation in migration rates can have significant effects on local adaptation, and is among the first to show how such variation affects niche evolution. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 30 May 2019 05:00:00 GMT “Evolution at the edge of expanding populations” https://amnat.org/an/newpapers/Sep-Deforet-A.html Read the Article (Just Accepted)Abstract Predicting evolution of expanding populations is critical to control biological threats such as invasive species and cancer metastasis. Expansion is primarily driven by reproduction and dispersal, but nature abounds with examples of evolution where organisms pay a reproductive cost to disperse faster. When does selection favor this ‘survival of the fastest?’ We searched for a simple rule, motivated by evolution experiments where swarming bacteria evolved into an hyperswarmer mutant which disperses ~100% faster but pays a growth cost of ~10% to make many copies of its flagellum. We analyzed a two-species model based on the Fisher equation to explain this observation: the population expansion rate (v) results from an interplay of growth (r) and dispersal (D) and is independent of the carrying capacity: v=2√rD. A mutant can take over the edge only if its expansion rate (v2) exceeds the expansion rate of the established species’ (v1); this simple condition (v2 > v1) determines the maximum cost in slower growth that a faster mutant can pay and still be able to take over. Numerical simulations and time-course experiments where we tracked evolution by imaging bacteria suggest that our findings are general: less favorable conditions delay but do not entirely prevent the success of the fastest. Thus, the expansion rate defines a traveling wave fitness, which could be combined with trade-offs to predict evolution of expanding populations. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704594">Read the Article</a></i> (Just Accepted)</p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>redicting evolution of expanding populations is critical to control biological threats such as invasive species and cancer metastasis. Expansion is primarily driven by reproduction and dispersal, but nature abounds with examples of evolution where organisms pay a reproductive cost to disperse faster. When does selection favor this ‘survival of the fastest?’ We searched for a simple rule, motivated by evolution experiments where swarming bacteria evolved into an hyperswarmer mutant which disperses ~100% faster but pays a growth cost of ~10% to make many copies of its flagellum. We analyzed a two-species model based on the Fisher equation to explain this observation: the population expansion rate (<i>v</i>) results from an interplay of growth (<i>r</i>) and dispersal (<i>D</i>) and is independent of the carrying capacity: <i>v</i>=2√<span style="text-decoration:overline;"><i>rD</i></span>. A mutant can take over the edge only if its expansion rate (<i>v</i><span style="font-size:70%; position:relative; bottom:-0.3em;">2</span>) exceeds the expansion rate of the established species’ (<i>v</i><span style="font-size:70%; position:relative; bottom:-0.3em;">1</span>); this simple condition (<i>v</i><span style="font-size:70%; position:relative; bottom:-0.3em;">2</span> &gt; <i>v</i><span style="font-size:70%; position:relative; bottom:-0.3em;">1</span>) determines the maximum cost in slower growth that a faster mutant can pay and still be able to take over. Numerical simulations and time-course experiments where we tracked evolution by imaging bacteria suggest that our findings are general: less favorable conditions delay but do not entirely prevent the success of the fastest. Thus, the expansion rate defines a traveling wave fitness, which could be combined with trade-offs to predict evolution of expanding populations. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 30 May 2019 05:00:00 GMT “Pollen on stigmas of herbarium specimens: a window into the impacts of a century of environmental disturbance on pollen transfer” https://amnat.org/an/newpapers/Sep-Johnson.html Read the Article (Just Accepted) A century of anthropogenic change in Hawaiʻi leaves a pollen ‘fingerprint’ on flower stigmas Biological collections provide a window into the past, and are the foundation of much of our knowledge about the diversity, range, and evolution of life. Billions of these specimens are preserved in natural history museums around the world. Recently, especially with the spread of new technologies such as genetic sequencing, mass digitization, and high resolution imaging, these collections are being revisited, and are yielding many exciting new insights into how global change is impacting life on earth. In this study, three University of Pittsburgh researchers, Anna Johnson, Maria Rebolleda-Gomez, and Tia-Lynn Ashman applied a novel method for gathering data from herbarium specimens to examine how pollination interactions have changed over longer ecological time scales than can usually be documented through long-term field studies. They collected pollen from herbarium specimen stigmas collected in the dry tropical forests of Hawaiʻi, an ecosystem that has experienced rapid habitat loss and disturbance over the last century. After counting and identifying the pollen grains to species, they compared the quantity and diversity of pollen which native dry forest plant species interacted with prior to 1950, and post 1950. They found that while the amount of pollen which these species received did not change dramatically, the identity of the pollen grains observed on herbarium stigmas was very different between the two time periods. This suggests that for plant species to survive in a rapidly changing world, they must be robust to shifts in species interactions, even for pollination, a key reproductive mutualism. The techniques demonstrated in this study hold promise for uncovering the history of pollination in other systems, especially those for which we currently lack an understanding of the types of interactions that species historically engaged in prior to widespread anthropogenic disturbances. Abstract Pollination is necessary for plant reproduction, but often highly susceptible to disruption, e.g., by habitat fragmentation and climate change. Here, we indirectly evaluated on a century time scale pollination interactions for species in one of the historically most disturbed habitats on earth—tropical dry forests of Hawaiʻi. We employed a novel method for acquiring a historical perspective on temporal change in pollination by characterizing pollen on stigmas of herbarium specimens from six remnant native species collected from 1909-2002. We determine whether temporal shifts occurred in 1) pollination quantity and quality, or 2) the composition of species interacting via pollen transfer. While pollen quantity remained constant, these remnant species interact with different species in modern times via pollen transfer than they did nearly 100 years ago. Species that are resilient to long-term environmental change may also be the ones subject to changes in pollination interactions. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704607">Read the Article</a></i> (Just Accepted)</p> <p><b>A century of anthropogenic change in Hawaiʻi leaves a pollen ‘fingerprint’ on flower stigmas </b></p><p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">B</span>iological collections provide a window into the past, and are the foundation of much of our knowledge about the diversity, range, and evolution of life. Billions of these specimens are preserved in natural history museums around the world. Recently, especially with the spread of new technologies such as genetic sequencing, mass digitization, and high resolution imaging, these collections are being revisited, and are yielding many exciting new insights into how global change is impacting life on earth.</p> <p>In this study, three University of Pittsburgh researchers, Anna Johnson, Maria Rebolleda-Gomez, and Tia-Lynn Ashman applied a novel method for gathering data from herbarium specimens to examine how pollination interactions have changed over longer ecological time scales than can usually be documented through long-term field studies. They collected pollen from herbarium specimen stigmas collected in the dry tropical forests of Hawaiʻi, an ecosystem that has experienced rapid habitat loss and disturbance over the last century. After counting and identifying the pollen grains to species, they compared the quantity and diversity of pollen which native dry forest plant species interacted with prior to 1950, and post 1950. They found that while the amount of pollen which these species received did not change dramatically, the identity of the pollen grains observed on herbarium stigmas was very different between the two time periods. This suggests that for plant species to survive in a rapidly changing world, they must be robust to shifts in species interactions, even for pollination, a key reproductive mutualism. The techniques demonstrated in this study hold promise for uncovering the history of pollination in other systems, especially those for which we currently lack an understanding of the types of interactions that species historically engaged in prior to widespread anthropogenic disturbances.</p><hr/> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">P</span>ollination is necessary for plant reproduction, but often highly susceptible to disruption, e.g., by habitat fragmentation and climate change. Here, we indirectly evaluated on a century time scale pollination interactions for species in one of the historically most disturbed habitats on earth&mdash;tropical dry forests of Hawaiʻi. We employed a novel method for acquiring a historical perspective on temporal change in pollination by characterizing pollen on stigmas of herbarium specimens from six remnant native species collected from 1909-2002. We determine whether temporal shifts occurred in 1) pollination quantity and quality, or 2) the composition of species interacting via pollen transfer. While pollen quantity remained constant, these remnant species interact with different species in modern times via pollen transfer than they did nearly 100 years ago. Species that are resilient to long-term environmental change may also be the ones subject to changes in pollination interactions.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 30 May 2019 05:00:00 GMT “Within-individual canalization contributes to age-related increases in trait repeatability: a longitudinal experiment in red knots” https://amnat.org/an/newpapers/Sep-Kok.html Read the Article (Just Accepted) Longitudinal lab experiment shows how canalization contributes to age-related changes in trait repeatability Individual variation is at the core of Darwin’s theory of evolution. Yet in ecology, variation between individuals was often considered as ‘noise’ or a nuisance. However, under changing environmental conditions, variation between individuals increases resilience for a population as a whole. Therefore, understanding what processes generate variation between individuals is important. This study focuses on individual variation and, in particular, what factors promote the development of variation between individuals. Researchers from the Royal Netherlands Institute for Sea Research (NL) and the University of Alberta (CA) looked at changes in bird ‘character’ with age, and if these changes are the unavoidable consequence of ageing or whether different experiences during life cause individuals to diverge. The scientists study the behavior of red knots—migratory shorebirds—exploring their surroundings in search of food. These birds differ in how they search (exploration behavior) and in the size of their stomachs (physiology). To investigate how these differences come about, 90 birds were brought into captivity either as juvenile or as adult, and then given identical experiences over the next two years. While the birds age, exploration behavior and stomach size are measured repeatedly to tease apart the effects of age, experience, and time in captivity on the amount of variation in both traits. If the birds’ individual experiences help maintain the differences between individuals, this variation should disappear during the course of the study because in these experiments, all birds have the same experience.Although it may seem easier to change one’s behavior than one’s physiology, these birds maintain their exploratory character while their stomach size changes. The next step is to follow the birds after their release back into the wild, to examine how the changes measured in the lab translate to real life. Abstract Age-related increases in the repeatable expression of labile phenotypic traits are often assumed to arise from an increase in among-individual variance due to differences in developmental plasticity or by means of state-behavior feedbacks. However, age-related increases in repeatability could also arise from a decrease in within-individual variance as a result of stabilizing trait expression, i.e. canalization. Here we describe age-related changes in within- and among-individual variance components in two correlated traits, gizzard mass and exploration behavior, in a medium-sized shorebird, the red knot (Calidris canutus). Increased repeatability of gizzard mass came about due to an increase in among-individual variance, unrelated to differences in developmental plasticity, together with decreases in within-individual variance, consistent with canalization. We also found canalization of exploration, but no age-related increase in overall repeatability, which suggests that showing predictable expression of exploration behavior may be advantageous from a very young age onward. Contrasts between juveniles and adults in the first year after their capture provide support for the idea that environmental conditions play a key role in generating among-individual variation in both gizzard mass and exploration behavior. Our study shows that stabilization of traits occurs under constant conditions: with increased exposure to predictable cues, individuals may become more certain in their assessment of the environment allowing traits to become canalized. De foarspelbere ûntwikkeling fan lichems- en gedrachseigenskippen: in eksperiment oer welhelberhyd fan eigenskippen by mientsen Alhoewol guon lichemseigenskippen fan jonge yndividuën hyltiten wer feroarje kinne, komme by it âlder wurden sokke eigenskippen ornaris dochs hyltiten mear fêst te lizzen. Soks kin komme troch it feroarjen fan yndividuele plastisiteit en troch weromkeppelingen tusken it gedrach en de steat fan sa’n bist. Yndividuele ferskillen yn it fêstlizzen fan eigenskippen fergrutsje de fariaasje tusken yndividuën. In technysk begrip om yndividuele fariaasje fan eigenskippen te kwantifisearjen is ‘repeatability’ (‘werhelberhyd’), mar it euvel is dat in taname fan dizze statistyske maat sawol komme kin troch in taname yn ‘e fariaasje tusken yndividuën en troch in ôfname fan de fariaasje binnen yndividuën; dit lêste neame wy ‘kanalisaasje’. Yn dit artikel beskriuwe wy hoe’t dizze twa boarnen fan fariaasje by it âlder wurden feroarje kinne by mientsen (Calidris canutus), en dat dogge wy oan ‘e hân fan twa besibbe eigenskippen: (1) it gewicht fan de spiermage, en (2) de wize werop mientsen yn in eksperimentele romte lytse stikjes waad ferkenne (der binne fûgels dy’t bot eksplorearje, en guon dy’t ôfwachtsje). It die bliken dat de werhelberhyd fan it magegewicht feroare troch tanimmende ferskillen tusken yndividuën en in ôfname fan de fariaasje binnen yndividuën, in kombinaasje fan plastisiteit en kanalisaasje dus. By eksploraasje-gedrach fûnen wy by it âlder wurden oanwizings foar kanalisaasje. Dat soe betsjutte kinne dat der foardielen binne om al op jonge leeftyd in bepaalde yndividuele wize fan eksploraasje oan te hâlden. Út in fergeliking tusken jonge en âlde fûgels (dy’t in ferskil yn ûntwikkeling yn it frije fjild wjerspegelje), blykte it bestean fan weromkeppelingen tusken de steat fan it lichem (magegewicht) en it gedrach (eksploraasje). Ús stúdzje lit lykwols foaral sjen dat eigenskippen, sels yn sitewaasjes dy’t net feroarje, fêst komme te lizzen. Miskien makket it fenomeen dat fûgels har omjouwing hyltiten better foarspelle kinne sokke kanalisaasje mooglik. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704593">Read the Article</a></i> (Just Accepted)</p> <p><b>Longitudinal lab experiment shows how canalization contributes to age-related changes in trait repeatability </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>ndividual variation is at the core of Darwin’s theory of evolution. Yet in ecology, variation between individuals was often considered as ‘noise’ or a nuisance. However, under changing environmental conditions, variation between individuals increases resilience for a population as a whole. Therefore, understanding what processes generate variation between individuals is important. </p><p>This study focuses on individual variation and, in particular, what factors promote the development of variation between individuals. Researchers from the Royal Netherlands Institute for Sea Research (NL) and the University of Alberta (CA) looked at changes in bird ‘character’ with age, and if these changes are the unavoidable consequence of ageing or whether different experiences during life cause individuals to diverge. </p><p>The scientists study the behavior of red knots—migratory shorebirds—exploring their surroundings in search of food. These birds differ in how they search (exploration behavior) and in the size of their stomachs (physiology). To investigate how these differences come about, 90 birds were brought into captivity either as juvenile or as adult, and then given identical experiences over the next two years. While the birds age, exploration behavior and stomach size are measured repeatedly to tease apart the effects of age, experience, and time in captivity on the amount of variation in both traits. If the birds’ individual experiences help maintain the differences between individuals, this variation should disappear during the course of the study because in these experiments, all birds have the same experience.</p><p>Although it may seem easier to change one’s behavior than one’s physiology, these birds maintain their exploratory character while their stomach size changes. The next step is to follow the birds after their release back into the wild, to examine how the changes measured in the lab translate to real life. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>ge-related increases in the repeatable expression of labile phenotypic traits are often assumed to arise from an increase in among-individual variance due to differences in developmental plasticity or by means of state-behavior feedbacks. However, age-related increases in repeatability could also arise from a decrease in within-individual variance as a result of stabilizing trait expression, i.e. canalization. Here we describe age-related changes in within- and among-individual variance components in two correlated traits, gizzard mass and exploration behavior, in a medium-sized shorebird, the red knot (<i>Calidris canutus</i>). Increased repeatability of gizzard mass came about due to an increase in among-individual variance, unrelated to differences in developmental plasticity, together with decreases in within-individual variance, consistent with canalization. We also found canalization of exploration, but no age-related increase in overall repeatability, which suggests that showing predictable expression of exploration behavior may be advantageous from a very young age onward. Contrasts between juveniles and adults in the first year after their capture provide support for the idea that environmental conditions play a key role in generating among-individual variation in both gizzard mass and exploration behavior. Our study shows that stabilization of traits occurs under constant conditions: with increased exposure to predictable cues, individuals may become more certain in their assessment of the environment allowing traits to become canalized. </p><h4>De foarspelbere ûntwikkeling fan lichems- en gedrachseigenskippen: in eksperiment oer welhelberhyd fan eigenskippen by mientsen </h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>lhoewol guon lichemseigenskippen fan jonge yndividuën hyltiten wer feroarje kinne, komme by it âlder wurden sokke eigenskippen ornaris dochs hyltiten mear fêst te lizzen. Soks kin komme troch it feroarjen fan yndividuele plastisiteit en troch weromkeppelingen tusken it gedrach en de steat fan sa’n bist. Yndividuele ferskillen yn it fêstlizzen fan eigenskippen fergrutsje de fariaasje tusken yndividuën. In technysk begrip om yndividuele fariaasje fan eigenskippen te kwantifisearjen is ‘repeatability’ (‘werhelberhyd’), mar it euvel is dat in taname fan dizze statistyske maat sawol komme kin troch in taname yn ‘e fariaasje tusken yndividuën en troch in ôfname fan de fariaasje <i>binnen</i> yndividuën; dit lêste neame wy ‘kanalisaasje’. Yn dit artikel beskriuwe wy hoe’t dizze twa boarnen fan fariaasje by it âlder wurden feroarje kinne by mientsen (<i>Calidris canutus</i>), en dat dogge wy oan ‘e hân fan twa besibbe eigenskippen: (1) it gewicht fan de spiermage, en (2) de wize werop mientsen yn in eksperimentele romte lytse stikjes waad ferkenne (der binne fûgels dy’t bot eksplorearje, en guon dy’t ôfwachtsje). It die bliken dat de werhelberhyd fan it magegewicht feroare troch tanimmende ferskillen tusken yndividuën en in ôfname fan de fariaasje binnen yndividuën, in kombinaasje fan plastisiteit en kanalisaasje dus. By eksploraasje-gedrach fûnen wy by it âlder wurden oanwizings foar kanalisaasje. Dat soe betsjutte kinne dat der foardielen binne om al op jonge leeftyd in bepaalde yndividuele wize fan eksploraasje oan te hâlden. Út in fergeliking tusken jonge en âlde fûgels (dy’t in ferskil yn ûntwikkeling yn it frije fjild wjerspegelje), blykte it bestean fan weromkeppelingen tusken de steat fan it lichem (magegewicht) en it gedrach (eksploraasje). Ús stúdzje lit lykwols foaral sjen dat eigenskippen, sels yn sitewaasjes dy’t net feroarje, fêst komme te lizzen. Miskien makket it fenomeen dat fûgels har omjouwing hyltiten better foarspelle kinne sokke kanalisaasje mooglik. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 29 May 2019 05:00:00 GMT “Antagonistic responses of exposure to sublethal temperatures: Adaptive phenotypic plasticity coincides with a reduction in organismal performance” https://amnat.org/an/newpapers/Sep-Gilbert.html Read the Article (Just Accepted) Exposure to stressful temperatures induces adaptive plasticity but constrains ecological and organismal performance Anthropogenic climate change is exposing populations to new environmental pressures that can lead to a variety of physiological, genetic, or behavioral responses. When novel environmental conditions cause phenotypic shifts in the absence of genetic change (i.e. phenotypic plasticity), oftentimes researchers only consider quantifying how traits-of-interest shift, without considering that particularly stressful stimuli might lead to other unforeseen phenotypic outcomes. Because many species are now predisposed to higher incidences of heat waves within their environment, exposure to sublethal temperatures is considered to be a trigger of adaptive phenotypic plasticity, otherwise called ‘heat hardening’. Heat hardening occurs when an individual is exposed to sublethal temperatures, and as a result they can temporarily tolerate higher temperatures than they could prior to heat shock. However, because the trigger of heat hardening is a stressful increase in body temperatures close to upper thermal tolerance limits, organisms might exhibit unforeseen physiological consequences. In this study, Gilbert and Miles show that for tree lizards in the Sonoran Desert, when heat hardening is expressed, lizards prefer cooler temperatures when they thermoregulate, and exhibit reductions in locomotor performance (maximal speed) throughout the response. They also find that because of these physiological costs, tree lizards are not fully able to exploit the adaptive nature of a higher heat tolerance, thus weakening their reliance on phenotypic plasticity as a buffer from temperature extremes. This study demonstrates that even though plasticity can be adaptive and beneficial, when organisms are exposed to extreme environmental stimuli, these stimuli might induce maladaptive responses in other traits leading to antagonistic interactions between the phenotypic shifts triggered by new environments. Abstract A&nbsp;fitness benefit of phenotypic plasticity is the ability of an organism to survive short-term, deleterious environmental fluctuations. Yet, the influence of selection on plasticity in modulating shifts in phenotypic traits remains unclear. Short-term phenotypic plasticity in thermal tolerance traits is attained by exposure to sublethal hot or cold temperatures (i.e. the hardening response). Heat hardening is expected to buffer organisms from the unpredictability of extreme thermal fluctuations in the environment so as to minimize interruptions in activity and enhance survival. However, exposure to sublethal temperatures might entail other phenotypic costs that constrain or inhibit the prolonged use of hardening responses across longer timescales. Here, we estimated the onset of the heat hardening response, physiological and behavioral shifts during heat hardening, and geographic variation in heat hardening using tree lizards (Urosaurus ornatus). Peak heat hardening occurred 6h after exposure to sublethal temperatures. We found that both preferred body temperatures and locomotor performance diminished following exposure to sublethal temperatures, and performance levels did not approach pre-exposure levels until after the peak hardening response. We also found support for intraspecific variation in the hardening response along an environmental gradient, where populations in more thermally variable environments exhibited stronger plastic responses and populations with higher baseline heat tolerances exhibited weaker plastic responses. Sublethal temperature exposure might induce adaptive plasticity in thermal tolerance, however we find that these responses entail other phenotypic shifts that might curtail chronic reliance on plasticity in thermal traits as a mechanism of responding to changes in thermal environments induced by climate warming. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704208">Read the Article</a></i> (Just Accepted)</p> <p><b>Exposure to stressful temperatures induces adaptive plasticity but constrains ecological and organismal performance </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>nthropogenic climate change is exposing populations to new environmental pressures that can lead to a variety of physiological, genetic, or behavioral responses. When novel environmental conditions cause phenotypic shifts in the absence of genetic change (i.e. phenotypic plasticity), oftentimes researchers only consider quantifying how traits-of-interest shift, without considering that particularly stressful stimuli might lead to other unforeseen phenotypic outcomes. Because many species are now predisposed to higher incidences of heat waves within their environment, exposure to sublethal temperatures is considered to be a trigger of adaptive phenotypic plasticity, otherwise called ‘heat hardening’. Heat hardening occurs when an individual is exposed to sublethal temperatures, and as a result they can temporarily tolerate higher temperatures than they could prior to heat shock. However, because the trigger of heat hardening is a stressful increase in body temperatures close to upper thermal tolerance limits, organisms might exhibit unforeseen physiological consequences. In this study, Gilbert and Miles show that for tree lizards in the Sonoran Desert, when heat hardening is expressed, lizards prefer cooler temperatures when they thermoregulate, and exhibit reductions in locomotor performance (maximal speed) throughout the response. They also find that because of these physiological costs, tree lizards are not fully able to exploit the adaptive nature of a higher heat tolerance, thus weakening their reliance on phenotypic plasticity as a buffer from temperature extremes. This study demonstrates that even though plasticity can be adaptive and beneficial, when organisms are exposed to extreme environmental stimuli, these stimuli might induce maladaptive responses in other traits leading to antagonistic interactions between the phenotypic shifts triggered by new environments. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>&nbsp;fitness benefit of phenotypic plasticity is the ability of an organism to survive short-term, deleterious environmental fluctuations. Yet, the influence of selection on plasticity in modulating shifts in phenotypic traits remains unclear. Short-term phenotypic plasticity in thermal tolerance traits is attained by exposure to sublethal hot or cold temperatures (i.e. the hardening response). Heat hardening is expected to buffer organisms from the unpredictability of extreme thermal fluctuations in the environment so as to minimize interruptions in activity and enhance survival. However, exposure to sublethal temperatures might entail other phenotypic costs that constrain or inhibit the prolonged use of hardening responses across longer timescales. Here, we estimated the onset of the heat hardening response, physiological and behavioral shifts during heat hardening, and geographic variation in heat hardening using tree lizards (<i>Urosaurus ornatus</i>). Peak heat hardening occurred 6h after exposure to sublethal temperatures. We found that both preferred body temperatures and locomotor performance diminished following exposure to sublethal temperatures, and performance levels did not approach pre-exposure levels until after the peak hardening response. We also found support for intraspecific variation in the hardening response along an environmental gradient, where populations in more thermally variable environments exhibited stronger plastic responses and populations with higher baseline heat tolerances exhibited weaker plastic responses. Sublethal temperature exposure might induce adaptive plasticity in thermal tolerance, however we find that these responses entail other phenotypic shifts that might curtail chronic reliance on plasticity in thermal traits as a mechanism of responding to changes in thermal environments induced by climate warming. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Omnivory in bees: Elevated trophic positions among all major bee families” https://amnat.org/an/newpapers/Sep-Steffan.html Read the Article (Just Accepted) Bees are omnivores, mainly because as larvae, they eat lots of ‘microbial meat’Bees are widely thought to derive all protein directly from floral resources. Recent findings suggest this is largely untrue. It appears that larval bees feed extensively on pollen-borne prey, as well as on the pollen, itself. These prey are the microbes that are suffused throughout a fermenting pollen-provision. Because the microbes are actively consuming the pollen, these herbivorous organisms represent ‘microbial meat’ within the pollen-provision. When a larval bee consumes aged pollen, the bee is consuming both microbial and plant biomass, assimilating the amino acids of microbial prey as well as those of the plant material—analogous to eating bacon bits in a salad. The degree to which a bee assimilates microbe-derived amino acids can be measured empirically as the trophic position of the bee (the more meat consumed, the higher the trophic position). Importantly, gut microbiota do not elevate the hosting animal’s trophic position. To assess the pervasiveness of bee omnivory, the trophic positions of bees representing the six major bee families on Earth were examined. Adult bees were collected over the course of two years, from the cranberry marshlands of Wisconsin to the forests of New York. There was consistent, significant evidence of elevated trophic positions among all the bees in the study (54 specimens across 14 species, 12 genera), suggesting that most bees, if not all, are omnivorous. Such reliance on microbial nutrition also suggests that pollen-borne microbes represent true symbionts for bees; thus, to conserve bee fauna, their microbial symbionts will require attention, too. Abstract As pollen- and nectar-foragers, bees have long been considered strictly herbivorous. Their pollen-provisions, however, are host to abundant microbial communities, which feed on the pollen before/while it is consumed by bee larvae. In the process, microbes convert pollen into a complex of plant and microbial components. Since microbes are analogous to metazoan consumers within trophic hierarchies, the pollen-eating microbes are, functionally, herbivores. When bee larvae consume a microbe-rich pollen complex, they ingest proteins from plant and microbial sources, thus should register as omnivores on the trophic “ladder.” We tested this hypothesis by examining the isotopic compositions of amino acids extracted from native bees collected in North America over multiple years. We measured bee trophic position across the six major bee families. Our findings indicate that bee trophic identity was consistently and significantly higher than that of strict herbivores, providing the first evidence that omnivory is ubiquitous among bee fauna. Such omnivory suggests that pollen-borne microbes represent an important protein source for larval bees, which introduces new questions as to the link between floral fungicide residues and bee development. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704281">Read the Article</a></i> (Just Accepted)</p> <p><b>Bees are omnivores, mainly because as larvae, they eat lots of ‘microbial meat’</b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">B</span>ees are widely thought to derive all protein directly from floral resources. Recent findings suggest this is largely untrue. It appears that larval bees feed extensively on pollen-borne prey, as well as on the pollen, itself. These prey are the microbes that are suffused throughout a fermenting pollen-provision. Because the microbes are actively consuming the pollen, these herbivorous organisms represent ‘microbial meat’ within the pollen-provision. When a larval bee consumes aged pollen, the bee is consuming both microbial and plant biomass, assimilating the amino acids of microbial prey as well as those of the plant material—analogous to eating bacon bits in a salad. The degree to which a bee assimilates microbe-derived amino acids can be measured empirically as the trophic position of the bee (the more meat consumed, the higher the trophic position). Importantly, gut microbiota do not elevate the hosting animal’s trophic position. To assess the pervasiveness of bee omnivory, the trophic positions of bees representing the six major bee families on Earth were examined. Adult bees were collected over the course of two years, from the cranberry marshlands of Wisconsin to the forests of New York. There was consistent, significant evidence of elevated trophic positions among all the bees in the study (54 specimens across 14 species, 12 genera), suggesting that most bees, if not all, are omnivorous. Such reliance on microbial nutrition also suggests that pollen-borne microbes represent true symbionts for bees; thus, to conserve bee fauna, their microbial symbionts will require attention, too. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>s pollen- and nectar-foragers, bees have long been considered strictly herbivorous. Their pollen-provisions, however, are host to abundant microbial communities, which feed on the pollen before/while it is consumed by bee larvae. In the process, microbes convert pollen into a complex of plant and microbial components. Since microbes are analogous to metazoan consumers within trophic hierarchies, the pollen-eating microbes are, functionally, herbivores. When bee larvae consume a microbe-rich pollen complex, they ingest proteins from plant and microbial sources, thus should register as omnivores on the trophic “ladder.” We tested this hypothesis by examining the isotopic compositions of amino acids extracted from native bees collected in North America over multiple years. We measured bee trophic position across the six major bee families. Our findings indicate that bee trophic identity was consistently and significantly higher than that of strict herbivores, providing the first evidence that omnivory is ubiquitous among bee fauna. Such omnivory suggests that pollen-borne microbes represent an important protein source for larval bees, which introduces new questions as to the link between floral fungicide residues and bee development. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Decreasing predator density and activity explain declining predation of insect prey along elevational gradients” https://amnat.org/an/newpapers/Sep-Camacho-A.html Read the Article (Just Accepted)Abstract Predation, which is a fundamental force in ecosystems, has been found to decrease in intensity with elevation and latitude. The mechanisms behind this pattern, however, remain unaddressed. Using visual sampling of potential predators and live flies as baits, we assessed predation patterns along 4000-meter elevation transects on either side of the equatorial Andes. We found that at the lower elevations around eighty percent of predation events on our insect baits were due to ants. The decline in predation with elevation was mainly driven by a decline in the abundance of ants, whose importance relative to other predators also declined. We show that both predator density and activity (predation rate per individual predator) decreased with elevation, thus ascribing specific mechanisms to known predation patterns. We suggest that changes in these two mechanisms may reflect changes in primary productivity and metabolic rate with temperature, factors of potential relevance across latitudinal and other macroecological gradients, in particular for ectotherm predators and prey. La disminuci&oacute;n en la densidad y actividad de depredadores explican la reducci&oacute;n en la depredaci&oacute;n de insectos presas a lo largo de gradientes de elevaci&oacute;n La depredaci&oacute;n, una fuerza fundamental en los ecosistemas, se ha encontrado que decrece en intensidad con la elevaci&oacute;n y la latitud. Los mecanismos detr&aacute;s de este patr&oacute;n, sin embargo, no han sido estudiados. En este trabajo, usando muestreos visuales de potenciales depredadores y moscas vivas como cebos, evaluamos patrones de depredaci&oacute;n en transectos realizados con una variaci&oacute;n altitudinal de 4000 metros en las dos caras de los Andes ecuatoriales. Encontramos que, en altitudes bajas, alrededor del ochenta porciento de los eventos de depredaci&oacute;n en nuestros insectos cebo fueron causados por hormigas. El decrecimiento en depredaci&oacute;n asociado con la variaci&oacute;n altitudinal fue principalmente causado por una reducci&oacute;n en la abundancia de hormigas, cuya importancia relativa respecto a otros depredadores tambi&eacute;n disminuy&oacute;. Mostramos que tanto la densidad como la actividad de depredadores (tasa individual de depredaci&oacute;n por depredador) decrecieron con la altitud, atribuyendo mecanismos a patrones de depredaci&oacute;n ya conocidos. Sugerimos que cambios en estos dos mecanismos pueden reflejar cambios en la productividad primaria y en la tasa metab&oacute;lica relacionados con la temperatura, factores potencialmente relevantes a lo largo de gradientes de latitud y otros gradientes macroecol&oacute;gicos, particularmente para presas y depredadores ectotermos. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704279">Read the Article</a></i> (Just Accepted)</p><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">P</span>redation, which is a fundamental force in ecosystems, has been found to decrease in intensity with elevation and latitude. The mechanisms behind this pattern, however, remain unaddressed. Using visual sampling of potential predators and live flies as baits, we assessed predation patterns along 4000-meter elevation transects on either side of the equatorial Andes. We found that at the lower elevations around eighty percent of predation events on our insect baits were due to ants. The decline in predation with elevation was mainly driven by a decline in the abundance of ants, whose importance relative to other predators also declined. We show that both predator density and activity (predation rate per individual predator) decreased with elevation, thus ascribing specific mechanisms to known predation patterns. We suggest that changes in these two mechanisms may reflect changes in primary productivity and metabolic rate with temperature, factors of potential relevance across latitudinal and other macroecological gradients, in particular for ectotherm predators and prey.</p> <h4>La disminuci&oacute;n en la densidad y actividad de depredadores explican la reducci&oacute;n en la depredaci&oacute;n de insectos presas a lo largo de gradientes de elevaci&oacute;n</h4> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">L</span>a depredaci&oacute;n, una fuerza fundamental en los ecosistemas, se ha encontrado que decrece en intensidad con la elevaci&oacute;n y la latitud. Los mecanismos detr&aacute;s de este patr&oacute;n, sin embargo, no han sido estudiados. En este trabajo, usando muestreos visuales de potenciales depredadores y moscas vivas como cebos, evaluamos patrones de depredaci&oacute;n en transectos realizados con una variaci&oacute;n altitudinal de 4000 metros en las dos caras de los Andes ecuatoriales. Encontramos que, en altitudes bajas, alrededor del ochenta porciento de los eventos de depredaci&oacute;n en nuestros insectos cebo fueron causados por hormigas. El decrecimiento en depredaci&oacute;n asociado con la variaci&oacute;n altitudinal fue principalmente causado por una reducci&oacute;n en la abundancia de hormigas, cuya importancia relativa respecto a otros depredadores tambi&eacute;n disminuy&oacute;. Mostramos que tanto la densidad como la actividad de depredadores (tasa individual de depredaci&oacute;n por depredador) decrecieron con la altitud, atribuyendo mecanismos a patrones de depredaci&oacute;n ya conocidos. Sugerimos que cambios en estos dos mecanismos pueden reflejar cambios en la productividad primaria y en la tasa metab&oacute;lica relacionados con la temperatura, factores potencialmente relevantes a lo largo de gradientes de latitud y otros gradientes macroecol&oacute;gicos, particularmente para presas y depredadores ectotermos.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Plastic senescence in the honeybee and the disposable soma theory” https://amnat.org/an/newpapers/Sep-da-Silva.html Read the Article (Just Accepted) The lifespan differences between honeybee castes help distinguish between different evolutionary theories of ageing Honeybee workers have much shorter lifespans than the queen not simply because they live more dangerous lives, but because they age faster. This tells us that ageing evolves as a consequence of an organism’s life history being adapted to its environment. Designation of an individual as a worker or a queen is not based on different sets of genes but on nutrition – a larva that is fed a protein-rich diet develops into a queen, otherwise she develops into a worker. As a worker, a bee ages so rapidly that she typically lives for only one month. In contrast, a queen may live for two years. But why should workers age more rapidly? Evolutionary theories of ageing tell us that natural selection becomes weaker with age simply because any individual has a lower probability of surviving to an old age than to a young age for reasons unrelated to ageing, such as accidental death. As a result, natural selection is less efficient at removing mutations that reduce survival or fertility at older ages, which may explain ageing. It follows from this that species that live more dangerous lives should age more rapidly. This logic also applies to honeybee workers, who perform high-risk duties outside the hive. However, since the designation of a worker is not based on a genetic difference from the queen, its higher rate of ageing must be due to different genes being turned on. The genes that are turned on in a worker are thought to invest the energy in its food in maintaining the bee’s body just enough to keep it functioning for its expected short lifespan, and as a result the bee ages rapidly. Any greater investment in maintenance would be wasteful. These results support an evolutionary theory of ageing, known as the disposable soma theory, that explains ageing as the consequence of organisms evolving an optimal strategy of investment in maintaining their bodies. Abstract The demonstration of lifespan plasticity in natural populations would provide a powerful test of evolutionary theories of senescence. Plastic senescence is not easily explained by mutation accumulation or antagonistic pleiotropy but is a corollary of the disposable soma theory. The lifespan differences among castes of the eusocial Hymenoptera are potentially some of the most striking and extreme examples of lifespan plasticity. Although these differences are often assumed to be plastic, this has never been demonstrated conclusively because differences in lifespan may be caused by the proximate effects of different levels of environmental hazard experienced by castes. Here, age-dependent and age-independent components of instantaneous mortality rates of the honeybee (Apis mellifera) were estimated from published lifetables for natural and semi-natural populations to determine whether differences in lifespan between queens and workers and between different types workers are indeed plastic. These differences in lifespan were found to be due to differences in the rate of actuarial senescence, which correlate positively with the rate of extrinsic mortality, in accordance with the central prediction of evolutionary theories of senescence. Although all three evolutionary theories of senescence could, in principle, explain such plastic senescence, given differential gene expression between castes or life stages, only the disposable soma theory adequately explains the adaptive regulation of somatic maintenance in response to different environmental conditions that appears to underlie lifespan plasticity. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704220">Read the Article</a></i> (Just Accepted)</p> <p><b>The lifespan differences between honeybee castes help distinguish between different evolutionary theories of ageing </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">H</span>oneybee workers have much shorter lifespans than the queen not simply because they live more dangerous lives, but because they age faster. This tells us that ageing evolves as a consequence of an organism’s life history being adapted to its environment. </p><p>Designation of an individual as a worker or a queen is not based on different sets of genes but on nutrition – a larva that is fed a protein-rich diet develops into a queen, otherwise she develops into a worker. As a worker, a bee ages so rapidly that she typically lives for only one month. In contrast, a queen may live for two years. But why should workers age more rapidly? Evolutionary theories of ageing tell us that natural selection becomes weaker with age simply because any individual has a lower probability of surviving to an old age than to a young age for reasons unrelated to ageing, such as accidental death. As a result, natural selection is less efficient at removing mutations that reduce survival or fertility at older ages, which may explain ageing. It follows from this that species that live more dangerous lives should age more rapidly. This logic also applies to honeybee workers, who perform high-risk duties outside the hive. However, since the designation of a worker is not based on a genetic difference from the queen, its higher rate of ageing must be due to different genes being turned on. The genes that are turned on in a worker are thought to invest the energy in its food in maintaining the bee’s body just enough to keep it functioning for its expected short lifespan, and as a result the bee ages rapidly. Any greater investment in maintenance would be wasteful. These results support an evolutionary theory of ageing, known as the disposable soma theory, that explains ageing as the consequence of organisms evolving an optimal strategy of investment in maintaining their bodies. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he demonstration of lifespan plasticity in natural populations would provide a powerful test of evolutionary theories of senescence. Plastic senescence is not easily explained by mutation accumulation or antagonistic pleiotropy but is a corollary of the disposable soma theory. The lifespan differences among castes of the eusocial Hymenoptera are potentially some of the most striking and extreme examples of lifespan plasticity. Although these differences are often assumed to be plastic, this has never been demonstrated conclusively because differences in lifespan may be caused by the proximate effects of different levels of environmental hazard experienced by castes. Here, age-dependent and age-independent components of instantaneous mortality rates of the honeybee (<i>Apis mellifera</i>) were estimated from published lifetables for natural and semi-natural populations to determine whether differences in lifespan between queens and workers and between different types workers are indeed plastic. These differences in lifespan were found to be due to differences in the rate of actuarial senescence, which correlate positively with the rate of extrinsic mortality, in accordance with the central prediction of evolutionary theories of senescence. Although all three evolutionary theories of senescence could, in principle, explain such plastic senescence, given differential gene expression between castes or life stages, only the disposable soma theory adequately explains the adaptive regulation of somatic maintenance in response to different environmental conditions that appears to underlie lifespan plasticity. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Intraspecific variation in worker body size makes North American bumble bees (<i>Bombus</i> spp.) less susceptible to decline” https://amnat.org/an/newpapers/Sep-Austin.html Read the Article (Just Accepted) Intraspecific variation in worker body size makes North American bumble bees less susceptible to population declines Population declines of bees are of broad interest, as bees are important pollinators of much of our wild and agricultural crops. While bee declines are likely caused by many factors, human-induced environmental changes are thought to be key culprits of these declines. A puzzle, however, is that not all bee species are declining – some are in fact thriving – which suggests differences between species in traits that enable responses to rapidly changed environments. In a new paper in The&nbsp;American Naturalist, M.&nbsp;W. Austin and A.&nbsp;S. Dunlap investigate traits in North American bumble bees (Bombus spp.) that may make certain species of bumble bees more susceptible to decline. They study two traits that may be particularly important for bees when encountering rapidly changed environments: 1) the amount of body size variation within a species (i.e. how close in size individual bees are) and 2) head size, a proxy for brain size and behavioral plasticity. High body size variation is likely adaptive within colonies; larger bees are more efficient workers, while smaller bees can withstand starvation for longer periods of time. Behavioral plasticity is thought to benefit species in changed environments, by allowing individuals to plastically change their behavior to novel environmental conditions. Using natural history collections from the Smithsonian, the American Museum of Natural History, the Field Museum, and the Illinois Natural History Survey, along with measures of bumble bee decline from the International Union for Conservation of Nature, the authors find that bumble bee species with low body size variation are more susceptible to decline, while species with higher body size variation are more likely to be thriving. Head size does not appear to affect a species’ likelihood of decline. These results suggest that high variation in body size enables bumble bees to successfully respond to environments altered by human activity, perhaps due to the benefits of body size variation within colonies. This study is part of Austin’s Ph.D. dissertation at the University of Missouri–St. Louis, where he became interested in this topic while considering why closely related species experience divergent population trends. Abstract Population declines have been documented in approximately one-third of bumble bee species. Certain drivers of these declines are known, however less is known about the interspecific trait differences that make certain species more susceptible to decline. Two traits, which have implications for responding to rapidly changed environments, may be particularly consequential for bumble bee populations: intraspecific body size variation and brain size. Bumble bee body size is highly variable and is likely adaptive at the colony level, and brain size correlates with cognitive traits (e.g. behavioral plasticity) in many groups. Trait variation and plasticity may buffer species against negative effects of rapidly changed environments. Using phylogenetically controlled analyses of 31 North American bumble bee species, we find higher intraspecific body size variation is associated with species having increased their relative abundance over time. However, this variation does not significantly interact with tongue length, another trait thought to influence bees’ decline susceptibility. Head size, a proxy for brain size, is not correlated with change in relative abundance. Our results support the hypothesis that variation in body size makes species less susceptible to decline in rapidly altered environments and suggests that this variation is important to the success of bumble bee populations. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704280">Read the Article</a></i> (Just Accepted)</p> <p><b>Intraspecific variation in worker body size makes North American bumble bees less susceptible to population declines </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>opulation declines of bees are of broad interest, as bees are important pollinators of much of our wild and agricultural crops. While bee declines are likely caused by many factors, human-induced environmental changes are thought to be key culprits of these declines. A puzzle, however, is that not all bee species are declining – some are in fact thriving – which suggests differences between species in traits that enable responses to rapidly changed environments. </p><p>In a new paper in <i>The&nbsp;American Naturalist</i>, M.&nbsp;W. Austin and A.&nbsp;S. Dunlap investigate traits in North American bumble bees (<i>Bombus</i> spp.) that may make certain species of bumble bees more susceptible to decline. They study two traits that may be particularly important for bees when encountering rapidly changed environments: 1) the amount of body size variation within a species (i.e. how close in size individual bees are) and 2) head size, a proxy for brain size and behavioral plasticity. High body size variation is likely adaptive within colonies; larger bees are more efficient workers, while smaller bees can withstand starvation for longer periods of time. Behavioral plasticity is thought to benefit species in changed environments, by allowing individuals to plastically change their behavior to novel environmental conditions. </p><p>Using natural history collections from the Smithsonian, the American Museum of Natural History, the Field Museum, and the Illinois Natural History Survey, along with measures of bumble bee decline from the International Union for Conservation of Nature, the authors find that bumble bee species with low body size variation are more susceptible to decline, while species with higher body size variation are more likely to be thriving. Head size does not appear to affect a species’ likelihood of decline. These results suggest that high variation in body size enables bumble bees to successfully respond to environments altered by human activity, perhaps due to the benefits of body size variation within colonies. </p><p>This study is part of Austin’s Ph.D. dissertation at the University of Missouri–St. Louis, where he became interested in this topic while considering why closely related species experience divergent population trends.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>opulation declines have been documented in approximately one-third of bumble bee species. Certain drivers of these declines are known, however less is known about the interspecific trait differences that make certain species more susceptible to decline. Two traits, which have implications for responding to rapidly changed environments, may be particularly consequential for bumble bee populations: intraspecific body size variation and brain size. Bumble bee body size is highly variable and is likely adaptive at the colony level, and brain size correlates with cognitive traits (e.g. behavioral plasticity) in many groups. Trait variation and plasticity may buffer species against negative effects of rapidly changed environments. Using phylogenetically controlled analyses of 31 North American bumble bee species, we find higher intraspecific body size variation is associated with species having increased their relative abundance over time. However, this variation does not significantly interact with tongue length, another trait thought to influence bees’ decline susceptibility. Head size, a proxy for brain size, is not correlated with change in relative abundance. Our results support the hypothesis that variation in body size makes species less susceptible to decline in rapidly altered environments and suggests that this variation is important to the success of bumble bee populations. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Destruction of spider webs and rescue of ensnared nestmates by a granivorous desert ant (<i>Veromessor pergandei</i>)” https://amnat.org/an/newpapers/Sep-Kwapich.html Read the Article (Just Accepted) Ants destroy spider webs and rescue trapped sisters that call for help Few prey species seek out and destroy the traps designed to capture them, and only a handful rescue group members in distress. That is why Kwapich and Hölldobler were surprised to discover that desert seed harvesting ants systematically dismantle spider webs constructed along their foraging routes, and retrieve sisters ensnared in spider silk. Animals that perform rescue behavior typically live in small groups with high-value individuals, but Veromessor pergandei form enormous societies that deploy up to 30,000 foragers each morning. To determine why colonies rescue seemingly disposable workers, the authors calculated the costs and benefits of web removal. They found that the seeds carried by foraging ants become tangled in undetected webs, reducing the total number of foraging trips individuals can take per day. By accounting for the length of a foraging career and number of trips per day, they estimated that unchecked spider predation could cost colonies 65,000 seeds per year. This is a high price to pay, because colonies need to gather enough resources to rear 600 new sisters each day. Many ant species clear debris from their foraging routes, but Kwapich and H&ouml;lldobler showed that V.&nbsp;pergandei foragers ignore novel objects, and even lack an innate ability to detect spider silk. Instead, ensnared ants release a chemical alarm signal, which stimulates a subset of large-bodied nestmates to remove surrounding webbing. Frozen ‘dummies’ marked with the same alarm compound were also rescued, and freed from their silk bindings. In essence, colonies only benefit from the removal of webs when workers are captured in them. Other seed harvesting ant species arrest foraging or change their foraging patterns in response to spiders. The authors propose that foraging on a single route during a limited temperature window, coupled with the necessary scale seed harvesting, led V.&nbsp;pergandei to its unusual defensive strategy. Abstract Prey species rarely seek-out and dismantle traps constructed by their predators. In the current study, we report an instance of targeted trap destruction by an invertebrate, and a novel context for rescue behavior. We found that foragers of the granivorous desert ant, Veromessor pergandei, identify and cooperatively dismantle spider webs (Araneae: Theridiidae, Steatoda spp. and Asagena sp.) During group foraging, workers ensnared in webs are recovered by sisters, who transport them to the nest and groom away their silk bindings. The presence of an ensnared nestmate and chemical alarm signal significantly increased the probability of web removal and nestmate retrieval. A subset of larger-bodied foragers participated in web removal, and 6.3% became tangled or were captured by spiders. Most animals that perform rescue behavior live in small groups, but V.&nbsp;pergandei colonies include tens of thousands of short-lived workers. To maintain their size, large colonies must collect enough seeds to produce 650 new ants each day. We hypothesize that the removal of spider webs allows for an unimpeded income of seeds on a single foraging path, during a brief daily temperature window. Despite the cost to individuals, webs are only recognized and removed when workers are captured in them. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704338">Read the Article</a></i> (Just Accepted) </p> <p><b>Ants destroy spider webs and rescue trapped sisters that call for help </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">F</span>ew prey species seek out and destroy the traps designed to capture them, and only a handful rescue group members in distress. That is why Kwapich and Hölldobler were surprised to discover that desert seed harvesting ants systematically dismantle spider webs constructed along their foraging routes, and retrieve sisters ensnared in spider silk. Animals that perform rescue behavior typically live in small groups with high-value individuals, but <i>Veromessor pergandei</i> form enormous societies that deploy up to 30,000 foragers each morning. </p><p>To determine why colonies rescue seemingly disposable workers, the authors calculated the costs and benefits of web removal. They found that the seeds carried by foraging ants become tangled in undetected webs, reducing the total number of foraging trips individuals can take per day. By accounting for the length of a foraging career and number of trips per day, they estimated that unchecked spider predation could cost colonies 65,000 seeds per year. This is a high price to pay, because colonies need to gather enough resources to rear 600 new sisters each day. </p><p>Many ant species clear debris from their foraging routes, but Kwapich and H&ouml;lldobler showed that <i>V.&nbsp;pergandei</i> foragers ignore novel objects, and even lack an innate ability to detect spider silk. Instead, ensnared ants release a chemical alarm signal, which stimulates a subset of large-bodied nestmates to remove surrounding webbing. Frozen &lsquo;dummies&rsquo; marked with the same alarm compound were also rescued, and freed from their silk bindings. In essence, colonies only benefit from the removal of webs when workers are captured in them. Other seed harvesting ant species arrest foraging or change their foraging patterns in response to spiders. The authors propose that foraging on a single route during a limited temperature window, coupled with the necessary scale seed harvesting, led <i>V.&nbsp;pergandei</i> to its unusual defensive strategy.</p> <hr/><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>rey species rarely seek-out and dismantle traps constructed by their predators. In the current study, we report an instance of targeted trap destruction by an invertebrate, and a novel context for rescue behavior. We found that foragers of the granivorous desert ant, <i>Veromessor pergandei</i>, identify and cooperatively dismantle spider webs (Araneae: Theridiidae, <i>Steatoda</i> spp. and <i>Asagena</i> sp.) During group foraging, workers ensnared in webs are recovered by sisters, who transport them to the nest and groom away their silk bindings. The presence of an ensnared nestmate and chemical alarm signal significantly increased the probability of web removal and nestmate retrieval. A subset of larger-bodied foragers participated in web removal, and 6.3% became tangled or were captured by spiders. Most animals that perform rescue behavior live in small groups, but <i>V.&nbsp;pergandei</i> colonies include tens of thousands of short-lived workers. To maintain their size, large colonies must collect enough seeds to produce 650 new ants each day. We hypothesize that the removal of spider webs allows for an unimpeded income of seeds on a single foraging path, during a brief daily temperature window. Despite the cost to individuals, webs are only recognized and removed when workers are captured in them. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 15 May 2019 05:00:00 GMT “Ecological release of the Anna’s Hummingbird during a northern range expansion” https://amnat.org/an/newpapers/Sep-Battey.html Read the Article (Just Accepted) Anna’s Hummingbird populations are booming in the northwest: A century of survey records shows how they got thereIn the early twentieth century, Anna’s Hummingbirds nested in coastal California and the Baja Peninsula, but today their breeding range extends from Arizona to British Columbia. How and when did they spread across western North America? New research conducted by Dr. C.&nbsp;J. Battey at the University of Washington used a century of survey and museum records to track the range and population growth of Anna’s Hummingbirds over time, and found that populations in the Pacific Northwest have been growing exponentially since the region was first colonized in the middle of the twentieth century. By comparing historic and modern climate records, the study shows that climate change is unlikely to explain the initial phases of the range expansion, but may play an increasingly important role in shaping the species’ range in the future. Instead, a combination of introduced plants and supplemental feeding appear to have allowed the species to escape limits on population growth in its native range and establish new breeding populations across Arizona and the Pacific Northwest during the 1960s and 70s. In one sign that populations may already be adapting to their new ranges, nest reports suggest that northern populations now delay the beginning of the nesting season by at least 16 days. The study provides a detailed historical record of this remarkable range expansion, and is a reminder of the profound ways in which humans have shaped the ranges and populations of native species over the last century. Abstract During range expansions species can experience rapid population growth if changes in climate or interspecific interactions remove limits on growth rates in novel habitats. Here I document a century of range expansion in the Anna’s Hummingbird (Calypte anna) and investigate the causes of its recent abundance through a combination of demographic, climatic, and phenological analyses. Christmas Bird Count records indicate that populations have been growing in California since the early twentieth century. Sites across the Pacific Northwest show striking fits to simple models of exponential growth following colonization in the 1960s and ’70s, and nest records indicate that the species now delays the start of the nesting season by at least 16 days in the north. Although the species now occurs in a much wider range of climates than prior to the range expansion, the fastest growing populations in the northwest are in regions with minimum breeding season temperatures similar to those occupied by the species in its native range. Range expansions in the Anna’s Hummingbird thus reflect an ecological release likely caused by a mix of introduced plants, human facilitation, and phenological acclimation that allowed a California native to expand across western North America. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704249">Read the Article</a></i> (Just Accepted)</p> <p><b>Anna’s Hummingbird populations are booming in the northwest: A century of survey records shows how they got there</b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n the early twentieth century, Anna’s Hummingbirds nested in coastal California and the Baja Peninsula, but today their breeding range extends from Arizona to British Columbia. How and when did they spread across western North America? New research conducted by Dr. C.&nbsp;J. Battey at the University of Washington used a century of survey and museum records to track the range and population growth of Anna’s Hummingbirds over time, and found that populations in the Pacific Northwest have been growing exponentially since the region was first colonized in the middle of the twentieth century. By comparing historic and modern climate records, the study shows that climate change is unlikely to explain the initial phases of the range expansion, but may play an increasingly important role in shaping the species’ range in the future. Instead, a combination of introduced plants and supplemental feeding appear to have allowed the species to escape limits on population growth in its native range and establish new breeding populations across Arizona and the Pacific Northwest during the 1960s and 70s. In one sign that populations may already be adapting to their new ranges, nest reports suggest that northern populations now delay the beginning of the nesting season by at least 16 days. The study provides a detailed historical record of this remarkable range expansion, and is a reminder of the profound ways in which humans have shaped the ranges and populations of native species over the last century.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">D</span>uring range expansions species can experience rapid population growth if changes in climate or interspecific interactions remove limits on growth rates in novel habitats. Here I document a century of range expansion in the Anna’s Hummingbird (<i>Calypte anna</i>) and investigate the causes of its recent abundance through a combination of demographic, climatic, and phenological analyses. Christmas Bird Count records indicate that populations have been growing in California since the early twentieth century. Sites across the Pacific Northwest show striking fits to simple models of exponential growth following colonization in the 1960s and ’70s, and nest records indicate that the species now delays the start of the nesting season by at least 16 days in the north. Although the species now occurs in a much wider range of climates than prior to the range expansion, the fastest growing populations in the northwest are in regions with minimum breeding season temperatures similar to those occupied by the species in its native range. Range expansions in the Anna’s Hummingbird thus reflect an ecological release likely caused by a mix of introduced plants, human facilitation, and phenological acclimation that allowed a California native to expand across western North America. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 08 May 2019 05:00:00 GMT “The equivocal mean age of parents in a cohort” https://amnat.org/an/newpapers/AugBienvenu.html Read the Article (Just Accepted) The mean age of parents of offspring produced by a cohort is not a good measure of the mean age at reproduction Open any demography textbook and you will find information on how to quantify reproductive timing. In particular, you should find an expression for the mean age at reproduction of a typical individual. This classic formula has been used for decades and is one of the most popular measures of generation time. Unfortunately, its well-accepted interpretation is incorrect; and the difference between what some reseachers have in mind and what they actually compute can be quite large in practice. By detailing the rigorous interpretation of the formula and providing an alternative expression for the mean age at reproduction, this article points out the need to think more deeply about what we mean by “average age at giving birth”. Abstract The mean age at which parents give birth is an important notion in demography, ecology and evolution, where it is used as a measure of generation time. A standard way to quantify it is to compute the mean age of the parents of all offspring produced by a cohort, and the resulting measure is thought to represent the mean age at which a typical parent produces offspring. In this note, I explain why this interpretation is problematic. I also introduce a new measure of the mean age at reproduction and show that it can be very different from the mean age of parents of offspring of a cohort. In particular, the mean age of parents of offspring of a cohort systematically overestimates the mean age at reproduction, and can even be greater than the expected lifespan of parents. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704110">Read the Article</a></i> (Just Accepted)</p> <p><b>The mean age of parents of offspring produced by a cohort is not a good measure of the mean age at reproduction </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">O</span>pen any demography textbook and you will find information on how to quantify reproductive timing. In particular, you should find an expression for the mean age at reproduction of a typical individual. This classic formula has been used for decades and is one of the most popular measures of generation time.</p> <p>Unfortunately, its well-accepted interpretation is incorrect; and the difference between what some reseachers have in mind and what they actually compute can be quite large in practice. By detailing the rigorous interpretation of the formula and providing an alternative expression for the mean age at reproduction, this article points out the need to think more deeply about what we mean by “average age at giving birth”.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he mean age at which parents give birth is an important notion in demography, ecology and evolution, where it is used as a measure of generation time. A standard way to quantify it is to compute the mean age of the parents of all offspring produced by a cohort, and the resulting measure is thought to represent the mean age at which a typical parent produces offspring. In this note, I explain why this interpretation is problematic. I also introduce a new measure of the mean age at reproduction and show that it can be very different from the mean age of parents of offspring of a cohort. In particular, the mean age of parents of offspring of a cohort systematically overestimates the mean age at reproduction, and can even be greater than the expected lifespan of parents. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 07 May 2019 05:00:00 GMT “Beta diversity patterns derived from island biogeography theory” https://amnat.org/an/newpapers/Sep-Lu.html Read the Article (Just Accepted) Beta diversity (Jaccard) is independent of the size of mainland species pool in the Island Biogeography Theory The island biogeography theory pioneered by MacArthur and Wilson has served as a foundation to understand the drivers of species richness for more than 50 years, but never tells us about what shapes beta diversity, i.e. the spatial variation of community composition among islands. A theoretical synthesis of island biogeography theory and beta diversity finally emerged at the call of a unified metacommunity framework to link ecological processes to more ecological patterns. Following MacArthur and Wilson’s original formulation (assuming species-equivalency), Muyang Lu, David Vasseur, and Walter Jetz first show that pairwise beta diversity (Jaccard dissimilarity) of two random islands is only determined by colonization and extinction rates of a species and independent of the size of species pool. This result runs counter to the prevailing belief that beta diversity increases with the size of species pool, with simulations further corroborating the conclusions under non-neutral scenarios. They further use an empirical bird dataset in Thousand Island Lake, China to demonstrate that beta diversity patterns is more powerful in detecting non-neutral processes than species richness. By adding a new dimension to the predictions of the half-century old island biogeography theory, this study opens the gate to investigate community assembly processes in a more systematic way and paves the way for a unified metacommunity theory. Abstract Metacommunity theory and its constituent Theory of Island Biogeography (TIB) have the potential to unify ecology across different scales. TIB has been successful in predicting alpha diversity patterns such as species-area relationships and species-abundance distributions, but lags behind in predicting spatial beta diversity patterns. In this study we use island biogeography theory as the starting point to integrate spatial beta diversity patterns into metacommunity theory. We first derive theoretical predictions for the expected beta diversity patterns under the classic MacArthur and Wilson framework where all species have equal colonization and extinction rates. We then test these predictions for the avian community composition of 42 islands (and 93 species) in the Thousand Island Lake, China. Our theoretical results corroborate that longer distance and smaller area lead to lower beta diversity, and further reveal that pairwise beta diversity is independent of the size of mainland species pool. We also find that for the partitioned pairwise beta diversity components, the turnover component increases with the ratio of extinction rates and colonization rates, while the nestedness component is a monotonic function of the ratio of extinction rates and colonization rates. For the empirical island system, we find that beta diversity patterns better distinguish a species-equivalent model from a species-nonequivalent model than alpha diversity patterns. Our findings suggest that beta diversity patterns provide a powerful tool in detecting non-neutral processes and our model has the potential to incorporate more biological realism in future analyses. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704181">Read the Article</a></i> (Just Accepted)</p> <p><b>Beta diversity (Jaccard) is independent of the size of mainland species pool in the Island Biogeography Theory </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he island biogeography theory pioneered by MacArthur and Wilson has served as a foundation to understand the drivers of species richness for more than 50 years, but never tells us about what shapes beta diversity, i.e. the spatial variation of community composition among islands. A theoretical synthesis of island biogeography theory and beta diversity finally emerged at the call of a unified metacommunity framework to link ecological processes to more ecological patterns. Following MacArthur and Wilson’s original formulation (assuming species-equivalency), Muyang Lu, David Vasseur, and Walter Jetz first show that pairwise beta diversity (Jaccard dissimilarity) of two random islands is only determined by colonization and extinction rates of a species and independent of the size of species pool. This result runs counter to the prevailing belief that beta diversity increases with the size of species pool, with simulations further corroborating the conclusions under non-neutral scenarios. They further use an empirical bird dataset in Thousand Island Lake, China to demonstrate that beta diversity patterns is more powerful in detecting non-neutral processes than species richness. By adding a new dimension to the predictions of the half-century old island biogeography theory, this study opens the gate to investigate community assembly processes in a more systematic way and paves the way for a unified metacommunity theory.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>etacommunity theory and its constituent Theory of Island Biogeography (TIB) have the potential to unify ecology across different scales. TIB has been successful in predicting alpha diversity patterns such as species-area relationships and species-abundance distributions, but lags behind in predicting spatial beta diversity patterns. In this study we use island biogeography theory as the starting point to integrate spatial beta diversity patterns into metacommunity theory. We first derive theoretical predictions for the expected beta diversity patterns under the classic MacArthur and Wilson framework where all species have equal colonization and extinction rates. We then test these predictions for the avian community composition of 42 islands (and 93 species) in the Thousand Island Lake, China. Our theoretical results corroborate that longer distance and smaller area lead to lower beta diversity, and further reveal that pairwise beta diversity is independent of the size of mainland species pool. We also find that for the partitioned pairwise beta diversity components, the turnover component increases with the ratio of extinction rates and colonization rates, while the nestedness component is a monotonic function of the ratio of extinction rates and colonization rates. For the empirical island system, we find that beta diversity patterns better distinguish a species-equivalent model from a species-nonequivalent model than alpha diversity patterns. Our findings suggest that beta diversity patterns provide a powerful tool in detecting non-neutral processes and our model has the potential to incorporate more biological realism in future analyses. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 30 Apr 2019 05:00:00 GMT “Can community structure causally determine dynamics of constituent species? A test using a host-parasite community” https://amnat.org/an/newpapers/Sep-Langendorf.html Read the Article (Just Accepted) Are community structures causal? Downward causation in a host-parasite community inferred from observational data Ecologists have long struggled with how features of an entire community – such as diversity or structural complexity – influence the functioning and dynamics of the member species. These community properties are do not exist physically, outside of the complex arrangements and dynamics of multiple species. How, if not mechanically, are they then able to influence the dynamics of the populations that constitute them? And more practically, how can ecologists test for this kind of causation down the organizational scales of an ecosystem? In this upcoming paper, Langendorf and Doak tackle these questions with observational data and causal discovery, applying the increasingly popular Convergent Cross Mapping method of inferring causality to time series data of a Slovakian host-parasite community where species abundances were recorded along with their interactions. They find that the populations of three host species were affected by how connected, clustered, and evenly-distributed interactions were across the entire community. This work offers evidence that structures in the configurations of ecological interactions affect constituent species. Just as importantly, it develops and demonstrates a method for identifying which community features are important to a given species of interest. Abstract Structures of communities have been widely studied with the assumption that they are not only a useful bookkeeping tool, but also can causally influence dynamics of the populations from which they emerge. However, convincing tests of this assumption have remained elusive, because generally the only way to alter a community property is by manipulating its constituent populations, thereby preventing independent measurements of effects on those populations. There is a growing body of evidence that methods like Convergent Cross Mapping (CCM) can be used to make inferences about causal interactions using state space reconstructions of coupled time series, a method that relies only on observational data. Here we show that CCM can be used to test the causal effects of community properties using a well-studied Slovakian rodent-ectoparasite community. CCM identified causal drivers across the organizational scales of this community, including evidence that host dynamics were influenced by the degree to which the community at large was connected and clustered. Our findings add to the growing literature on the importance of community structures in disease dynamics and argue for a broader use of causal inference in the analysis of community dynamics. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704182">Read the Article</a></i> (Just Accepted)</p> <p><b>Are community structures causal? Downward causation in a host-parasite community inferred from observational data </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">E</span>cologists have long struggled with how features of an entire community – such as diversity or structural complexity – influence the functioning and dynamics of the member species. These community properties are do not exist physically, outside of the complex arrangements and dynamics of multiple species. How, if not mechanically, are they then able to influence the dynamics of the populations that constitute them? And more practically, how can ecologists test for this kind of causation down the organizational scales of an ecosystem? In this upcoming paper, Langendorf and Doak tackle these questions with observational data and causal discovery, applying the increasingly popular Convergent Cross Mapping method of inferring causality to time series data of a Slovakian host-parasite community where species abundances were recorded along with their interactions. They find that the populations of three host species were affected by how connected, clustered, and evenly-distributed interactions were across the entire community. This work offers evidence that structures in the configurations of ecological interactions affect constituent species. Just as importantly, it develops and demonstrates a method for identifying which community features are important to a given species of interest. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>tructures of communities have been widely studied with the assumption that they are not only a useful bookkeeping tool, but also can causally influence dynamics of the populations from which they emerge. However, convincing tests of this assumption have remained elusive, because generally the only way to alter a community property is by manipulating its constituent populations, thereby preventing independent measurements of effects on those populations. There is a growing body of evidence that methods like Convergent Cross Mapping (CCM) can be used to make inferences about causal interactions using state space reconstructions of coupled time series, a method that relies only on observational data. Here we show that CCM can be used to test the causal effects of community properties using a well-studied Slovakian rodent-ectoparasite community. CCM identified causal drivers across the organizational scales of this community, including evidence that host dynamics were influenced by the degree to which the community at large was connected and clustered. Our findings add to the growing literature on the importance of community structures in disease dynamics and argue for a broader use of causal inference in the analysis of community dynamics. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 30 Apr 2019 05:00:00 GMT “Experimental evidence that metamorphosis alleviates genomic conflict” https://amnat.org/an/newpapers/Sep-Goedert.html Read the Article (Just Accepted) Metamorphosis changes integration between traits and alleviates ontogenetic conflict across amphibian life stages Metamorphosis is a remarkable characteristic of many amphibians, marking the transition from an aquatic to a terrestrial life stage. Metamorphosis is a complex and costly process and the benefits of metamorphosis have long puzzled biologists. One possibility is that the morphological changes that occur during metamorphosis allow natural selection to shape the two life stages independently of each other in their respective habitats. Given that tadpoles and frogs are life stages of a single individual, and must be formed from the same genetic material, one might wonder whether it is possible to adapt to one environment without paying a cost of adaptation in the other. In this study, Goedert and Calsbeek use wood frogs to investigate the so-called ‘adaptive decoupling hypothesis’. The researchers performed controlled mattings in the laboratory and reared hundreds of tadpoles through metamorphosis. Their breeding design allowed them to test for patterns of integration in the inheritance of tadpole and frog morphology – for instance, the researchers were able to ask whether having genes for a long tail as a tadpole would lead to long legged frogs. They showed that, although there is some genetic integration between tadpole and frog morphologies, the degree of such integration was much lower between life stages than within either tadpoles or frogs. This study provides some of the first evidence that metamorphosis may have evolved to allow natural selection to shape a single genome into two very different life forms. Abstract Whenever genetically correlated traits experience antagonistic selection, an adaptive response in one trait can lead to a maladaptive response in the correlated trait. This is a form of genome-level conflict that can have important evolutionary consequences by impeding organisms from reaching their adaptive optima. Antagonistic selection should be pervasive in organisms with complex life histories because larval and adult life stages specialize in dramatically different environments. Since individuals express larval and adult morphologies from a single genome, genomic conflict across ontogenetic stages should also be prevalent. Using wood frogs as a study system, we measured natural selection on larval and post-metamorphic life stages, and estimated genetic correlations among traits. Alternative life stages experienced a mix of both antagonistic and congruent viability selection. The integration between traits changed over the course of metamorphosis, reducing genetic correlations that cause conflict. Our results provide novel experimental evidence that metamorphosis can alleviate genomic conflict by partitioning life history stages into modules that can more readily respond to selection. These results highlight the adaptive potential of metamorphosis as a means to avoid ecological specialization trade-offs. Moreover, they provide insights into the prevalence and evolutionary maintenance of complex life cycles. Evidência experimental de que a metamorfose reduz conflito genômico Quando pressões seletivas antagonistas atuam em características geneticamente correlacionadas, a resposta adaptativa de uma dessas características pode resultar em uma resposta maladaptativa na característica correlacionada. Tal situação representa uma forma de conflito genômico que pode ter importantes consequências evolutivas ao impedir organismos de atingir seu valor adaptativo máximo. Espera-se que seleção antagonista seja comum em organismos com ciclo de vida complexos, porque estágios larvais e adultos são especialistas em ambientes muito diferentes. Além disso, como indivíduos expressam morfologias de larva e adulto utilizando um mesmo genoma, o conflito genômico entre esses estágios ontogenéticos deve ser prevalente. Usando sapos (Rana sylvatica) como organismo modelo, medimos seleção natural tanto no estágio larval quanto em estágios pós-metamorfose, e estimamos correlações genéticas entre características de ambos estágios. Os diferentes estágios ontogenéticos apresentaram uma combinação de seleção de viabilidade em direções antagonistas e congruentes. O nível de integração entre características variou ao longo do processo de metamorfose, havendo redução de correlações genéticas que poderiam causar conflito genômico. Nossos resultados demostram evidência de que o processo de metamorfose pode aliviar o conflito genômico ao particionar os estágios ontogenéticos em módulos, permitindo que estes respondam mais rapidamente a forças seletivas. Esses resultados enfatizam o potencial adaptativo da metamorfose como uma forma de evitar demandas conflitantes durante especialização ecológica dos estágios de vida. Mais ainda, esses resultados contribuem para o entendimento da prevalência e manutenção evolutiva de ciclos de vida complexos. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704183">Read the Article</a></i> (Just Accepted) </p> <p><b>Metamorphosis changes integration between traits and alleviates ontogenetic conflict across amphibian life stages </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>etamorphosis is a remarkable characteristic of many amphibians, marking the transition from an aquatic to a terrestrial life stage. Metamorphosis is a complex and costly process and the benefits of metamorphosis have long puzzled biologists. One possibility is that the morphological changes that occur during metamorphosis allow natural selection to shape the two life stages independently of each other in their respective habitats. Given that tadpoles and frogs are life stages of a single individual, and must be formed from the same genetic material, one might wonder whether it is possible to adapt to one environment without paying a cost of adaptation in the other. </p> <p>In this study, Goedert and Calsbeek use wood frogs to investigate the so-called ‘adaptive decoupling hypothesis’. The researchers performed controlled mattings in the laboratory and reared hundreds of tadpoles through metamorphosis. Their breeding design allowed them to test for patterns of integration in the inheritance of tadpole and frog morphology – for instance, the researchers were able to ask whether having genes for a long tail as a tadpole would lead to long legged frogs. They showed that, although there is some genetic integration between tadpole and frog morphologies, the degree of such integration was much lower between life stages than within either tadpoles or frogs. This study provides some of the first evidence that metamorphosis may have evolved to allow natural selection to shape a single genome into two very different life forms. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>henever genetically correlated traits experience antagonistic selection, an adaptive response in one trait can lead to a maladaptive response in the correlated trait. This is a form of genome-level conflict that can have important evolutionary consequences by impeding organisms from reaching their adaptive optima. Antagonistic selection should be pervasive in organisms with complex life histories because larval and adult life stages specialize in dramatically different environments. Since individuals express larval and adult morphologies from a single genome, genomic conflict across ontogenetic stages should also be prevalent. Using wood frogs as a study system, we measured natural selection on larval and post-metamorphic life stages, and estimated genetic correlations among traits. Alternative life stages experienced a mix of both antagonistic and congruent viability selection. The integration between traits changed over the course of metamorphosis, reducing genetic correlations that cause conflict. Our results provide novel experimental evidence that metamorphosis can alleviate genomic conflict by partitioning life history stages into modules that can more readily respond to selection. These results highlight the adaptive potential of metamorphosis as a means to avoid ecological specialization trade-offs. Moreover, they provide insights into the prevalence and evolutionary maintenance of complex life cycles. </p> <h4>Evidência experimental de que a metamorfose reduz conflito genômico</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">Q</span>uando pressões seletivas antagonistas atuam em características geneticamente correlacionadas, a resposta adaptativa de uma dessas características pode resultar em uma resposta maladaptativa na característica correlacionada. Tal situação representa uma forma de conflito genômico que pode ter importantes consequências evolutivas ao impedir organismos de atingir seu valor adaptativo máximo. Espera-se que seleção antagonista seja comum em organismos com ciclo de vida complexos, porque estágios larvais e adultos são especialistas em ambientes muito diferentes. Além disso, como indivíduos expressam morfologias de larva e adulto utilizando um mesmo genoma, o conflito genômico entre esses estágios ontogenéticos deve ser prevalente. Usando sapos (<i>Rana sylvatica</i>) como organismo modelo, medimos seleção natural tanto no estágio larval quanto em estágios pós-metamorfose, e estimamos correlações genéticas entre características de ambos estágios. Os diferentes estágios ontogenéticos apresentaram uma combinação de seleção de viabilidade em direções antagonistas e congruentes. O nível de integração entre características variou ao longo do processo de metamorfose, havendo redução de correlações genéticas que poderiam causar conflito genômico. Nossos resultados demostram evidência de que o processo de metamorfose pode aliviar o conflito genômico ao particionar os estágios ontogenéticos em módulos, permitindo que estes respondam mais rapidamente a forças seletivas. Esses resultados enfatizam o potencial adaptativo da metamorfose como uma forma de evitar demandas conflitantes durante especialização ecológica dos estágios de vida. Mais ainda, esses resultados contribuem para o entendimento da prevalência e manutenção evolutiva de ciclos de vida complexos. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 30 Apr 2019 05:00:00 GMT “Dormancy in metacommunities” https://amnat.org/an/newpapers/AugWisnoski.html Read the Article (Just Accepted)Metacommunity ecology has primarily focused on how dispersal influences biodiversity across a landscape. However, many species possess the ability to engage in dormancy, a reversible state of reduced metabolism, which allows them to “disperse through time”. As a result, colonization of a local community can occur from an internal “seed bank” of dormant organisms, not just from other habitat patches, as is commonly assumed in metacommunity theory. Using simulation models, the authors show that dormancy can modify patterns of biodiversity across spatial scales in the metacommunity. The influence of dormancy on these patterns may further depend on whether dispersal and dormancy are correlated (positively or negatively). In an analysis of aquatic invertebrates that live in tropical bromeliads, the authors find evidence for correlations between dispersal and dormancy strategies. Evidence from the literature suggests colonization from the seed bank is typically most important following local disturbances or in spatially isolated communities where dispersal is limiting. Our work also has implications for understanding and predicting species invasions. More broadly, dormancy in the context of metacommunity ecology may provide alternative explanations for commonly observed biodiversity patterns and could improve our understanding of eco-evolutionary dynamics and ecosystem functioning across spatial scales. Abstract Although metacommunity ecology has improved our understanding of how dispersal affects community structure and dynamics across spatial scales, it has yet to adequately account for dormancy. Dormancy is a reversible state of reduced metabolic activity that enables temporal dispersal within the metacommunity. Dormancy is also a metacommunity-level process because it can covary with spatial dispersal and affect diversity across spatial scales. We develop a framework to integrate dispersal and dormancy, focusing on the covariation they exhibit, to predict how dormancy modifies the importance of species interactions, dispersal, and historical contingencies in metacommunities. We used empirical and modeling approaches to demonstrate the utility of this framework. We examined case studies of microcrustaceans in ephemeral ponds, where dormancy underlies metacommunity dynamics, and identified constraints on the dispersal and dormancy strategies of bromeliad-dwelling invertebrates. Using simulations, we showed that dormancy can alter classic metacommunity patterns of diversity in ways that depend on dispersal–dormancy covariation and spatiotemporal environmental variability. We propose that dormancy may also facilitate evolution-mediated priority effects if locally adapted seed banks prevent colonization by more dispersal-limited species. Last, we present testable predictions for the implications of dormancy in metacommunities, some of which may fundamentally alter our understanding of metacommunity ecology. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704168">Read the Article</a></i> (Just Accepted)</p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>etacommunity ecology has primarily focused on how dispersal influences biodiversity across a landscape. However, many species possess the ability to engage in dormancy, a reversible state of reduced metabolism, which allows them to “disperse through time”. As a result, colonization of a local community can occur from an internal “seed bank” of dormant organisms, not just from other habitat patches, as is commonly assumed in metacommunity theory. </p><p>Using simulation models, the authors show that dormancy can modify patterns of biodiversity across spatial scales in the metacommunity. The influence of dormancy on these patterns may further depend on whether dispersal and dormancy are correlated (positively or negatively). In an analysis of aquatic invertebrates that live in tropical bromeliads, the authors find evidence for correlations between dispersal and dormancy strategies. Evidence from the literature suggests colonization from the seed bank is typically most important following local disturbances or in spatially isolated communities where dispersal is limiting. Our work also has implications for understanding and predicting species invasions. More broadly, dormancy in the context of metacommunity ecology may provide alternative explanations for commonly observed biodiversity patterns and could improve our understanding of eco-evolutionary dynamics and ecosystem functioning across spatial scales.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>lthough metacommunity ecology has improved our understanding of how dispersal affects community structure and dynamics across spatial scales, it has yet to adequately account for dormancy. Dormancy is a reversible state of reduced metabolic activity that enables temporal dispersal within the metacommunity. Dormancy is also a metacommunity-level process because it can covary with spatial dispersal and affect diversity across spatial scales. We develop a framework to integrate dispersal and dormancy, focusing on the covariation they exhibit, to predict how dormancy modifies the importance of species interactions, dispersal, and historical contingencies in metacommunities. We used empirical and modeling approaches to demonstrate the utility of this framework. We examined case studies of microcrustaceans in ephemeral ponds, where dormancy underlies metacommunity dynamics, and identified constraints on the dispersal and dormancy strategies of bromeliad-dwelling invertebrates. Using simulations, we showed that dormancy can alter classic metacommunity patterns of diversity in ways that depend on dispersal–dormancy covariation and spatiotemporal environmental variability. We propose that dormancy may also facilitate evolution-mediated priority effects if locally adapted seed banks prevent colonization by more dispersal-limited species. Last, we present testable predictions for the implications of dormancy in metacommunities, some of which may fundamentally alter our understanding of metacommunity ecology. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Mon, 29 Apr 2019 05:00:00 GMT “Playing out Liem’s Paradox: opportunistic piscivory across Lake Tanganyikan cichlids” https://amnat.org/an/newpapers/Aug-Golcher-Benavides.html Read the Article (Just Accepted) Researchers report diet switching by morphologically specialized cichlids as consequence of unusual concentrations of clupeidsCichlid fishes are celebrated for their often extreme feeding adaptations and unique feeding strategies: Lobochilotes labiatus extracts invertebrates from rock crevices using its enlarged lips, Perissodus microlepis’s feeding on scales from other fishes is linked to their striking mouth asymmetry, Tropheus duboisi crops algae growing on the rocky substrate using teeth located at the jaw-edges of their subterminal mouths. Karel Liem (1980) first noted that cichlid fishes are not only remarkable dietary specialists, but also can act as jacks-of-all-trades. However, evidence for the dietary flexibility of cichlids comes from laboratory studies, and it is unclear whether cichlid fishes in the wild actually feed on resources other than the ones they have adaptations for. We report field observations of dietary switching by multiple cichlid species in Lake Tanganyika as a consequence of a transient school of juvenile sardines; and discuss this evidence in the framework of Liem’s paradox. Robinson and Wilson (1998) solved Liem’s paradox by demonstrating that extreme dietary specializations can theoretically be maintained as long as they do not preclude the ability to exploit other broadly accessible food resources. Rare pulses of “easy prey” could determine the fate of endemic species with small population size across ecosystems. Abstract Trophic specialization is a key feature of the diversity of cichlid fish adaptive radiations. However, Liem (1980) observed that even species with highly specialized trophic morphologies have dietary flexibility, enabling them to exploit episodic food resources opportunistically. Evidence for dietary flexibility comes largely from laboratory studies, and it is unclear whether cichlid fishes undergo diet shifts in the wild. We report observations of diet switching by multiple cichlid species in Lake Tanganyika as a consequence of unusual concentrations of schooling juvenile clupeid fishes. Fish species with varying degrees of trophic specialization converged on a single prey: juvenile sardines that are also endemic to Lake Tanganyika (Stolothrissa tanganicae and Limnothrissa miodon). We provide evidence for cichlid species acting as jacks-of-all-trades and discuss this evidence in the framework of Liem’s classic paradox: that trophic specialization does not preclude dietary flexibility. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704169">Read the Article</a></i> (Just Accepted)</p> <p><b>Researchers report diet switching by morphologically specialized cichlids as consequence of unusual concentrations of clupeids</b></p><p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">C</span>ichlid fishes are celebrated for their often extreme feeding adaptations and unique feeding strategies: <i>Lobochilotes labiatus</i> extracts invertebrates from rock crevices using its enlarged lips, <i>Perissodus microlepis</i>&rsquo;s feeding on scales from other fishes is linked to their striking mouth asymmetry, <i>Tropheus duboisi</i> crops algae growing on the rocky substrate using teeth located at the jaw-edges of their subterminal mouths. Karel Liem (1980) first noted that cichlid fishes are not only remarkable dietary specialists, but also can act as jacks-of-all-trades. However, evidence for the dietary flexibility of cichlids comes from laboratory studies, and it is unclear whether cichlid fishes in the wild actually feed on resources other than the ones they have adaptations for. We report field observations of dietary switching by multiple cichlid species in Lake Tanganyika as a consequence of a transient school of juvenile sardines; and discuss this evidence in the framework of Liem&rsquo;s paradox. Robinson and Wilson (1998) solved Liem&rsquo;s paradox by demonstrating that extreme dietary specializations can theoretically be maintained as long as they do not preclude the ability to exploit other broadly accessible food resources. Rare pulses of &ldquo;easy prey&rdquo; could determine the fate of endemic species with small population size across ecosystems.</p> <hr /> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">T</span>rophic specialization is a key feature of the diversity of cichlid fish adaptive radiations. However, Liem (1980) observed that even species with highly specialized trophic morphologies have dietary flexibility, enabling them to exploit episodic food resources opportunistically. Evidence for dietary flexibility comes largely from laboratory studies, and it is unclear whether cichlid fishes undergo diet shifts in the wild. We report observations of diet switching by multiple cichlid species in Lake Tanganyika as a consequence of unusual concentrations of schooling juvenile clupeid fishes. Fish species with varying degrees of trophic specialization converged on a single prey: juvenile sardines that are also endemic to Lake Tanganyika (<i>Stolothrissa tanganicae</i> and <i>Limnothrissa miodon</i>). We provide evidence for cichlid species acting as jacks-of-all-trades and discuss this evidence in the framework of Liem&rsquo;s classic paradox: that trophic specialization does not preclude dietary flexibility.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Mon, 29 Apr 2019 05:00:00 GMT “Coevolution creates complex mosaics across large landscapes” https://amnat.org/an/newpapers/AugFernandes.html Read the Article (Just Accepted)Does our understanding of the interplay between species interactions and patterns of diversity still apply when we go from local to regional or continental scales? It is now widely recognized that species interactions play a major role in influencing evolutionary rates, trajectories, and outcomes, but how does the spatial organization of these interactions affect the way species’ traits are distributed in space? Using mathematical models to describe coevolutionary dynamics in a landscape where the interactions vary from mutualism to antagonism, Fernandes and collaborators investigate how coevolution affects the spatial patterns of phenotypes, when considering large spatial scales and different structures of geographic mosaics of selection. One of the main results of this work is the formation of large clusters of phenotypes, in many cases much larger than the spatial aggregation of sites with the same interaction outcome. This result leads to the implications that (i) phenotype distributions can not be directly obtained from the outcomes of local interactions, and that (ii) local interactions can not be simply inferred from local patterns of trait distributions alone. Focusing on how the magnitude of selection, the spatial distribution of interactions and gene flow influence the spatial patterns of phenotypes, this work calls attention to the importance of comprehending coevolutionary dynamics in this context, and also the many ways in which these dynamics can be affected by human-driven habitat fragmentation in natural landscapes. Abstract The spatial distribution of populations can influence the evolutionary outcome of species interactions. The variation in direction and strength of selection across local communities creates geographic selection mosaics that, when combined with gene flow and genomic processes such as genome duplication or hybridization, can fuel ongoing coevolution. A fundamental problem to solve is how coevolution proceeds when many populations that vary in their ecological outcomes are connected across large landscapes. Here we use a lattice model to explore this problem. Our results show that the complex interrelationships among the elements of the geographic mosaic of coevolution can lead to the formation of clusters of populations with similar phenotypes that are larger than expected by local selection. Our results indicate that neither the spatial distribution of phenotypes nor the spatial differences in magnitude and direction of selection alone dictate coevolutionary dynamics: the geographic mosaic of coevolution affects formation of phenotypic clusters, which in turn affect the spatial and temporal dynamics of coevolution. Because the formation of large phenotypic clusters depends on gene flow, we predict current habitat fragmentation will change the outcomes of geographic mosaics, coupling spatial patterns in selection and phenotypes. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704157">Read the Article</a></i> (Just Accepted)</p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">D</span>oes our understanding of the interplay between species interactions and patterns of diversity still apply when we go from local to regional or continental scales? It is now widely recognized that species interactions play a major role in influencing evolutionary rates, trajectories, and outcomes, but how does the spatial organization of these interactions affect the way species’ traits are distributed in space? Using mathematical models to describe coevolutionary dynamics in a landscape where the interactions vary from mutualism to antagonism, Fernandes and collaborators investigate how coevolution affects the spatial patterns of phenotypes, when considering large spatial scales and different structures of geographic mosaics of selection. One of the main results of this work is the formation of large clusters of phenotypes, in many cases much larger than the spatial aggregation of sites with the same interaction outcome. This result leads to the implications that (i) phenotype distributions can not be directly obtained from the outcomes of local interactions, and that (ii) local interactions can not be simply inferred from local patterns of trait distributions alone. Focusing on how the magnitude of selection, the spatial distribution of interactions and gene flow influence the spatial patterns of phenotypes, this work calls attention to the importance of comprehending coevolutionary dynamics in this context, and also the many ways in which these dynamics can be affected by human-driven habitat fragmentation in natural landscapes. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he spatial distribution of populations can influence the evolutionary outcome of species interactions. The variation in direction and strength of selection across local communities creates geographic selection mosaics that, when combined with gene flow and genomic processes such as genome duplication or hybridization, can fuel ongoing coevolution. A fundamental problem to solve is how coevolution proceeds when many populations that vary in their ecological outcomes are connected across large landscapes. Here we use a lattice model to explore this problem. Our results show that the complex interrelationships among the elements of the geographic mosaic of coevolution can lead to the formation of clusters of populations with similar phenotypes that are larger than expected by local selection. Our results indicate that neither the spatial distribution of phenotypes nor the spatial differences in magnitude and direction of selection alone dictate coevolutionary dynamics: the geographic mosaic of coevolution affects formation of phenotypic clusters, which in turn affect the spatial and temporal dynamics of coevolution. Because the formation of large phenotypic clusters depends on gene flow, we predict current habitat fragmentation will change the outcomes of geographic mosaics, coupling spatial patterns in selection and phenotypes. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Mon, 29 Apr 2019 05:00:00 GMT “Generation time measures the trade-off between survival and reproduction in a life cycle” https://amnat.org/an/newpapers/AugGiaimo.html Read the Article Generation time measures the trade-off between survival and reproduction in a life cycle The African elephant or the desert tortoise can live up to 80 years in a dangerous world without medicine: Shouldn’t we do genetics of longevity on them to get their secret? Yes, in principle. But it would very impractical. Looking at differences between only two generations of these animals would exceed the life expectancy of a human researcher and the usual horizon of science funding. For this reason too, animal models of aging and longevity, like the fruit fly and the mice, are usually chosen that are fast-lived in comparison to humans. Mutations that extend lifespan in these animals are isolated in the hope of finding similar human genes. But results from this approach may not transfer smoothly to humans. Mutants with longer life are often less fertile. Optimization theory shows that the reproductive cost of a slightly increased longevity in a species is measured by the average age at parenthood in the species, the so-called generation time. A 1% increase in survival, for example, imposes a percentage cost in reproduction equal to the generation time. But fruit flies usually give birth at around 11 days, while humans need on average 20 to 30 years. Therefore, studies on animal models may underestimate the fertility price of enhanced longevity in humans. While short-lived animals are likely to remain important and very useful models in the genetics of longevity, this result helps us to better understand their potential limitations. Abstract Survival and fertility are the two most basic components of fitness and they drive the evolution of a life cycle. A trade-off between them is usually present: when survival increases, fertility decreases – and vice versa. Here we show that, at an evolutionary optimum, the generation time is a measure of the strength of the trade-off between overall survival and overall fertility in a life cycle. Our result both helps to explain the known fact that the generation time describes the speed of living in the slow-fast continuum of life cycles and may have implications for the extrapolation from model organisms of longevity to humans. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704155">Read the Article</a></i></p> <p><b>Generation time measures the trade-off between survival and reproduction in a life cycle </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he African elephant or the desert tortoise can live up to 80 years in a dangerous world without medicine: Shouldn’t we do genetics of longevity on them to get their secret? Yes, in principle. But it would very impractical. Looking at differences between only two generations of these animals would exceed the life expectancy of a human researcher and the usual horizon of science funding. For this reason too, animal models of aging and longevity, like the fruit fly and the mice, are usually chosen that are fast-lived in comparison to humans. Mutations that extend lifespan in these animals are isolated in the hope of finding similar human genes. But results from this approach may not transfer smoothly to humans. </p> <p>Mutants with longer life are often less fertile. Optimization theory shows that the reproductive cost of a slightly increased longevity in a species is measured by the average age at parenthood in the species, the so-called generation time. A 1% increase in survival, for example, imposes a percentage cost in reproduction equal to the generation time. But fruit flies usually give birth at around 11 days, while humans need on average 20 to 30 years. Therefore, studies on animal models may underestimate the fertility price of enhanced longevity in humans. While short-lived animals are likely to remain important and very useful models in the genetics of longevity, this result helps us to better understand their potential limitations.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>urvival and fertility are the two most basic components of fitness and they drive the evolution of a life cycle. A trade-off between them is usually present: when survival increases, fertility decreases – and vice versa. Here we show that, at an evolutionary optimum, the generation time is a measure of the strength of the trade-off between overall survival and overall fertility in a life cycle. Our result both helps to explain the known fact that the generation time describes the speed of living in the slow-fast continuum of life cycles and may have implications for the extrapolation from model organisms of longevity to humans. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Mon, 29 Apr 2019 05:00:00 GMT “Lifetime fitness, sex-specific life history, and the maintenance of a polyphenism” https://amnat.org/an/newpapers/AugLackey.html Read the Article Long-term data (27 years) reveals lifetime fitness differs between the sexes of each morph of tiger salamanders Studying survival and reproduction within populations provides windows into the processes and mechanisms that underlie the evolutionary origins and maintenance of diversity. Lackey et al. examine a striking type of variation within some salamander populations where a larva can develop into one of two morphs based on its body size and competition: one morph undergoes metamorphosis to become a terrestrial adult, whereas the other retains its larval characteristics and matures as an aquatic adult. While these morphs have long fascinated evolutionary biologists, even gracing the cover of Gould’s landmark Ontogeny and Phylogeny (1977), long-term studies of lifetime costs and benefits are necessary to determine which factors promote the maintenance of two morphs within the same population. Howard Whiteman spearheaded an ongoing long-term research program in 1990 in a population of Arizona Tiger Salamanders in the Rocky Mountains of Colorado. Lackey et al. use 27 years of data from this population to test for differences between each morph and sex in (1) lifetime reproduction, (2) timing of development and reproduction, and (3) consequences of environmental variation across time and space. The authors find that males of the aquatic morph and females of the terrestrial morph have higher lifetime reproduction than the other morph-sex combinations. Thus, sex-specific payoffs likely contribute to maintaining the two morphs in this population. Intriguingly, the morphs achieve these outcomes via different developmental and reproductive strategies. Although the environment shapes which morph a larva becomes, it seems to have little effect on differences between morphs in lifetime reproduction. These results demonstrate how differences in lifetime reproduction can contribute to maintaining trait variation within a population and emphasize the importance of studying reproductive differences between the sexes. Abstract Polyphenisms, alternative morphs produced through plasticity, can reveal the evolutionary and ecological processes that initiate and maintain diversity within populations. We examined lifetime fitness consequences of two morphs in a polyphenic population of Arizona Tiger Salamanders using a 27-year data set with 1,317 adults and 6,862 captures across eight generations. Larval salamanders develop into either an aquatic paedomorph that retains larval traits and stays in its natal pond or a terrestrial metamorph that undergoes metamorphosis. To evaluate the adaptive significance of this polyphenism, we compared lifetime reproductive success of each morph and assessed how life history strategies and spatiotemporal variation explained fitness. We found sex-specific differences in lifetime fitness between morphs. For males, paedomorphs had more reproductive opportunities than metamorphs when we accounted for the potential mating advantage of larger males. For females, in contrast, metamorphs had higher estimated egg production than paedomorphs. Life history strategies differed between morphs largely because the morphs maximized different ends of the trade-off between age at first reproduction and longevity. Spatiotemporal variation affected larval more than adult life history traits with little to no effect on lifetime fitness. Thus, environmental variation likely explains differences in morph production across time and space but contributes little to lifetime fitness differences between morphs and sexes. Our long-term study and measures of lifetime fitness provide unique insight into the complex selective regimes potentially acting on each morph and sex. Our findings motivate future work to examine how sex-specific selection may contribute to the maintenance of polyphenism. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704156">Read the Article</a></i></p> <p><b>Long-term data (27 years) reveals lifetime fitness differs between the sexes of each morph of tiger salamanders </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>tudying survival and reproduction within populations provides windows into the processes and mechanisms that underlie the evolutionary origins and maintenance of diversity. Lackey et al. examine a striking type of variation within some salamander populations where a larva can develop into one of two morphs based on its body size and competition: one morph undergoes metamorphosis to become a terrestrial adult, whereas the other retains its larval characteristics and matures as an aquatic adult. While these morphs have long fascinated evolutionary biologists, even gracing the cover of Gould’s landmark <i>Ontogeny and Phylogeny</i> (1977), long-term studies of lifetime costs and benefits are necessary to determine which factors promote the maintenance of two morphs within the same population. Howard Whiteman spearheaded an ongoing long-term research program in 1990 in a population of Arizona Tiger Salamanders in the Rocky Mountains of Colorado. Lackey et al. use 27 years of data from this population to test for differences between each morph and sex in (1) lifetime reproduction, (2) timing of development and reproduction, and (3) consequences of environmental variation across time and space. The authors find that males of the aquatic morph and females of the terrestrial morph have higher lifetime reproduction than the other morph-sex combinations. Thus, sex-specific payoffs likely contribute to maintaining the two morphs in this population. Intriguingly, the morphs achieve these outcomes via different developmental and reproductive strategies. Although the environment shapes which morph a larva becomes, it seems to have little effect on differences between morphs in lifetime reproduction. These results demonstrate how differences in lifetime reproduction can contribute to maintaining trait variation within a population and emphasize the importance of studying reproductive differences between the sexes.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>olyphenisms, alternative morphs produced through plasticity, can reveal the evolutionary and ecological processes that initiate and maintain diversity within populations. We examined lifetime fitness consequences of two morphs in a polyphenic population of Arizona Tiger Salamanders using a 27-year data set with 1,317 adults and 6,862 captures across eight generations. Larval salamanders develop into either an aquatic paedomorph that retains larval traits and stays in its natal pond or a terrestrial metamorph that undergoes metamorphosis. To evaluate the adaptive significance of this polyphenism, we compared lifetime reproductive success of each morph and assessed how life history strategies and spatiotemporal variation explained fitness. We found sex-specific differences in lifetime fitness between morphs. For males, paedomorphs had more reproductive opportunities than metamorphs when we accounted for the potential mating advantage of larger males. For females, in contrast, metamorphs had higher estimated egg production than paedomorphs. Life history strategies differed between morphs largely because the morphs maximized different ends of the trade-off between age at first reproduction and longevity. Spatiotemporal variation affected larval more than adult life history traits with little to no effect on lifetime fitness. Thus, environmental variation likely explains differences in morph production across time and space but contributes little to lifetime fitness differences between morphs and sexes. Our long-term study and measures of lifetime fitness provide unique insight into the complex selective regimes potentially acting on each morph and sex. Our findings motivate future work to examine how sex-specific selection may contribute to the maintenance of polyphenism. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Mon, 29 Apr 2019 05:00:00 GMT “Resolving the paradox of environmental quality and sociality: the ecological causes and consequences of cooperative breeding in two lineages of birds” https://amnat.org/an/newpapers/AugLin-A.html Read the Article (Just Accepted) Social animals occupy larger species range size Abstract Cooperatively breeding animals occur in virtually every ecosystem on earth. Comparative and biogeographic studies suggest that both benign and harsh, as well as stable and fluctuating, environments can favor the evolution of cooperative breeding behavior. The fact that cooperative societies occur in environments of such contrasting quality creates a paradox of environmental quality and sociality. The dual-benefits framework—which leads to the prediction that the ecological consequences of sociality (e.g. range size) vary depending on the benefits that individuals of each species receive by forming social groups—offers a potential resolution to this paradox. Here we use a case study of two avian lineages, starlings (Sturnidae) and hornbills (Bucerotidae), in which environmental unpredictability appears to have opposite effects on the evolution of cooperation to test the dual-benefits framework. Consistent with previous work, harsh and unpredictable environments promote cooperative breeding behavior in starlings, which in turn leads to larger geographic ranges. However, cooperatively breeding hornbills occur in benign and stable environments, but sociality does not influence range size. Our study suggests that the paradox of environmental quality and sociality arises largely because cooperative breeding is an umbrella term, encompassing social species that form groups for different reasons. We demonstrate that differentiating among the functional causes of social group formation is critical for developing a predictive framework for understanding the evolution of cooperative breeding behavior. 解決環境品質和社會性演化的悖論:促進兩類鳥類類群中合作生殖演化的生態原因與其後果 林宇恆,詹仕凡,Dustin R. Rubenstein,劉彥廷,沈聖峰 地球上幾乎每個生態系統均可見合作生殖的動物。比較研究和生物地理學研究顯示,良好與嚴苛、以及穩定和變動的環境皆有利於合作生殖行為的演化。合作生殖物種在這些品質相異的環境中存在的事實造成了環境品質和社會性演化的悖論。我們的雙重群體利益理論預測:社會性的生態後果(例如物種的地理分布範圍大小)取決於每個物種的個體透過組成社會群體所獲得的利益,因此這理論提供了對這一悖論的潛在解決方案。由於環境不可預測性對椋鳥科和犀鳥科這兩個鳥類類群合作生殖的演化,有相反的影響,我們就使用兩個鳥類類群,進行案例研究以測試雙重群體利益理論。與過去的研究結果一致的是,嚴酷和不可預測的環境促進了椋鳥的合作繁殖行為,因而使椋鳥有更大的物種地理分布範圍。然而,合作繁殖的犀鳥在良好和穩定的環境中出現,但其合作生殖與否則不影響物種的分布範圍大小。我們的研究表明,環境品質和社會性演化的悖論的形成主要是因為合作生殖是一個概括性術語,包含因不同生態原因而形成群體的社會性物種。我們的研究證明,區分社會群體形成的生態原因,對於進一步發展用於理解合作生殖行為演化的預測理論至為關鍵。 More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704090">Read the Article</a></i> (Just Accepted)</p> <p><strong>Social animals occupy larger species range size </strong></p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">C</span>ooperatively breeding animals occur in virtually every ecosystem on earth. Comparative and biogeographic studies suggest that both benign and harsh, as well as stable and fluctuating, environments can favor the evolution of cooperative breeding behavior. The fact that cooperative societies occur in environments of such contrasting quality creates a paradox of environmental quality and sociality. The dual-benefits framework—which leads to the prediction that the ecological consequences of sociality (e.g. range size) vary depending on the benefits that individuals of each species receive by forming social groups—offers a potential resolution to this paradox. Here we use a case study of two avian lineages, starlings (Sturnidae) and hornbills (Bucerotidae), in which environmental unpredictability appears to have opposite effects on the evolution of cooperation to test the dual-benefits framework. Consistent with previous work, harsh and unpredictable environments promote cooperative breeding behavior in starlings, which in turn leads to larger geographic ranges. However, cooperatively breeding hornbills occur in benign and stable environments, but sociality does not influence range size. Our study suggests that the paradox of environmental quality and sociality arises largely because cooperative breeding is an umbrella term, encompassing social species that form groups for different reasons. We demonstrate that differentiating among the functional causes of social group formation is critical for developing a predictive framework for understanding the evolution of cooperative breeding behavior. </p> <h4>解決環境品質和社會性演化的悖論:促進兩類鳥類類群中合作生殖演化的生態原因與其後果</h4> <p>林宇恆,詹仕凡,Dustin R. Rubenstein,劉彥廷,沈聖峰</p> <p>地球上幾乎每個生態系統均可見合作生殖的動物。比較研究和生物地理學研究顯示,良好與嚴苛、以及穩定和變動的環境皆有利於合作生殖行為的演化。合作生殖物種在這些品質相異的環境中存在的事實造成了環境品質和社會性演化的悖論。我們的雙重群體利益理論預測:社會性的生態後果(例如物種的地理分布範圍大小)取決於每個物種的個體透過組成社會群體所獲得的利益,因此這理論提供了對這一悖論的潛在解決方案。由於環境不可預測性對椋鳥科和犀鳥科這兩個鳥類類群合作生殖的演化,有相反的影響,我們就使用兩個鳥類類群,進行案例研究以測試雙重群體利益理論。與過去的研究結果一致的是,嚴酷和不可預測的環境促進了椋鳥的合作繁殖行為,因而使椋鳥有更大的物種地理分布範圍。然而,合作繁殖的犀鳥在良好和穩定的環境中出現,但其合作生殖與否則不影響物種的分布範圍大小。我們的研究表明,環境品質和社會性演化的悖論的形成主要是因為合作生殖是一個概括性術語,包含因不同生態原因而形成群體的社會性物種。我們的研究證明,區分社會群體形成的生態原因,對於進一步發展用於理解合作生殖行為演化的預測理論至為關鍵。</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 24 Apr 2019 05:00:00 GMT “Environmental veto synchronizes mast seeding in four contrasting tree species” https://amnat.org/an/newpapers/AugBogdziewicz.html Read the Article (Just Accepted) Adverse weather events can synchronize trees reproduction Variable, synchronized seed production, called masting, is a widespread reproductive strategy in plants. How plants are able to synchronize reproduction is a longstanding question. One leading idea is that plants need to accumulate sufficient resources after depletion following seeding, which creates annual variability of reproduction. Synchrony is then induced by the efficiency of mass flowering for outcross pollination. Plants that reproduce asynchronously do not spent resources on seeds due to pollination failure, so they flower again and again until other plants do it as well, when flowers can get pollinated. Similar resource carry-over can be induced by external factors preventing reproduction – environmental veto – like frost or other adverse weather events. In this case, preventing plants from developing seeds in one year helps to put all plants on the same reproductive schedule. The authors of this study used four species differing in their masting strategies: Two species (pine and rowan) are “flowering masting” species, i.e. plants where mast seeding is driven by variable production of flowers. Two other species were oaks, and these are “fruiting masting” species, i.e. species where annual variation in seed production is a consequence of variable ripening with relatively constant flower production. Based on that difference in life history, they predicted that synchronization in the “flowering masting” species would be driven by density-dependent pollination success, while in the second group by correlated environmental veto. Indeed, positive density-dependence of pollination was much stronger in rowan and pine, while veto was much more frequent in oaks. However, in all four species, the veto was strong enough to drive synchrony without the need to invoke any other mechanism. Susceptibility to adverse weather conditions may benefit masting species, as it allows them to synchronize seed production. Abstract Synchronized and variable reproduction by perennial plants, called mast seeding, is a major reproductive strategy of trees. The need to accumulate sufficient resources after depletion following fruiting (resource budget), the efficiency of mass flowering for outcross pollination (pollen coupling), or the external factors preventing reproduction (environmental veto) could all synchronize masting. We used seed production data for four species (Quercus ilex, Q.&nbsp;humilis, Sorbus aucuparia, Pinus albicaulis) to parametrize resource budget models of masting. Based on species life history characteristics, we hypothesized that pollen coupling should synchronize reproduction in S.&nbsp;aucuparia and P.&nbsp;albicaulis, while in Q.&nbsp;ilex and Q.&nbsp;humilis environmental veto should be a major factor. Pollen coupling was stronger in S.&nbsp;aucuparia and P.&nbsp;albicaulis than in oaks, while veto was more frequent in the latter. Yet, in all species, costs of reproduction were too small to impose a replenishment period. A synchronous environmental veto, in the presence of environmental stochasticity, was sufficient to produce observed variability and synchrony in reproduction. In the past, vetoes like frost events that prevent reproduction have been perceived as negative for plants. In fact, they could be selectively favored as a way to create mast seeding. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704111">Read the Article</a></i> (Just Accepted)</p> <p><b>Adverse weather events can synchronize trees reproduction </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">V</span>ariable, synchronized seed production, called masting, is a widespread reproductive strategy in plants. How plants are able to synchronize reproduction is a longstanding question. One leading idea is that plants need to accumulate sufficient resources after depletion following seeding, which creates annual variability of reproduction. Synchrony is then induced by the efficiency of mass flowering for outcross pollination. Plants that reproduce asynchronously do not spent resources on seeds due to pollination failure, so they flower again and again until other plants do it as well, when flowers can get pollinated. Similar resource carry-over can be induced by external factors preventing reproduction – environmental veto – like frost or other adverse weather events. In this case, preventing plants from developing seeds in one year helps to put all plants on the same reproductive schedule. </p><p>The authors of this study used four species differing in their masting strategies: Two species (pine and rowan) are “flowering masting” species, i.e. plants where mast seeding is driven by variable production of flowers. Two other species were oaks, and these are “fruiting masting” species, i.e. species where annual variation in seed production is a consequence of variable ripening with relatively constant flower production. Based on that difference in life history, they predicted that synchronization in the “flowering masting” species would be driven by density-dependent pollination success, while in the second group by correlated environmental veto. Indeed, positive density-dependence of pollination was much stronger in rowan and pine, while veto was much more frequent in oaks. However, in all four species, the veto was strong enough to drive synchrony without the need to invoke any other mechanism. Susceptibility to adverse weather conditions may benefit masting species, as it allows them to synchronize seed production.</p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>ynchronized and variable reproduction by perennial plants, called mast seeding, is a major reproductive strategy of trees. The need to accumulate sufficient resources after depletion following fruiting (resource budget), the efficiency of mass flowering for outcross pollination (pollen coupling), or the external factors preventing reproduction (environmental veto) could all synchronize masting. We used seed production data for four species (<i>Quercus ilex, Q.&nbsp;humilis, Sorbus aucuparia, Pinus albicaulis</i>) to parametrize resource budget models of masting. Based on species life history characteristics, we hypothesized that pollen coupling should synchronize reproduction in <i>S.&nbsp;aucuparia</i> and <i>P.&nbsp;albicaulis</i>, while in <i>Q.&nbsp;ilex</i> and <i>Q.&nbsp;humilis</i> environmental veto should be a major factor. Pollen coupling was stronger in <i>S.&nbsp;aucuparia</i> and <i>P.&nbsp;albicaulis</i> than in oaks, while veto was more frequent in the latter. Yet, in all species, costs of reproduction were too small to impose a replenishment period. A synchronous environmental veto, in the presence of environmental stochasticity, was sufficient to produce observed variability and synchrony in reproduction. In the past, vetoes like frost events that prevent reproduction have been perceived as negative for plants. In fact, they could be selectively favored as a way to create mast seeding. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “Are pheromones key to unlocking cryptic lizard diversity?” https://amnat.org/an/newpapers/AugZozaya-A.html Read the Article (Just Accepted) Abstract Animals use mating traits to compete for, attract, and choose mates. Because mating traits influence mate choice, the divergence of mating traits between populations can result in reproductive isolation. This can occur without associated morphological divergence, producing reproductively isolated ‘cryptic species’ that are visually indistinguishable. Thus, identifying the mating traits in morphologically conservative groups is key to resolving diversity and speciation processes. Lizards contain many such groups, with phylogeographic studies often revealing highly divergent but morphologically cryptic lineages within species. Considering that cryptic lizard species can be sympatric but morphologically indistinguishable, we hypothesize that candidate species will exhibit divergent pheromones and that pheromones will have typically diverged more than morphology. To test this, we used gas chromatography to characterize pheromones (epidermal pore secretions) from 10 genetically divergent lineages of the Bynoe’s gecko (Heteronotia binoei) species complex in northern Australia. Multivariate analyses of pheromone blends and morphology indicate that pheromones are lineage-specific and have diverged relatively more than morphology. Such specificity suggests that pheromones influence behavioral isolation in this morphologically conservative lizard radiation. These results suggest that pheromone data may unlock the tremendous ‘cryptic’ diversity currently being uncovered in many lizard groups. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704059">Read the Article</a></i> (Just Accepted)</p> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">A</span>nimals use mating traits to compete for, attract, and choose mates. Because mating traits influence mate choice, the divergence of mating traits between populations can result in reproductive isolation. This can occur without associated morphological divergence, producing reproductively isolated &lsquo;cryptic species&rsquo; that are visually indistinguishable. Thus, identifying the mating traits in morphologically conservative groups is key to resolving diversity and speciation processes. Lizards contain many such groups, with phylogeographic studies often revealing highly divergent but morphologically cryptic lineages within species. Considering that cryptic lizard species can be sympatric but morphologically indistinguishable, we hypothesize that candidate species will exhibit divergent pheromones and that pheromones will have typically diverged more than morphology. To test this, we used gas chromatography to characterize pheromones (epidermal pore secretions) from 10 genetically divergent lineages of the Bynoe&rsquo;s gecko (<em>Heteronotia binoei</em>) species complex in northern Australia. Multivariate analyses of pheromone blends and morphology indicate that pheromones are lineage-specific and have diverged relatively more than morphology. Such specificity suggests that pheromones influence behavioral isolation in this morphologically conservative lizard radiation. These results suggest that pheromone data may unlock the tremendous &lsquo;cryptic&rsquo; diversity currently being uncovered in many lizard groups.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: georgia; font-size: large;"><em>More forthcoming papers</em> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “Individual variation in the social plasticity of water dragons” https://amnat.org/an/newpapers/AugStrickland-A.html Read the ArticleAbstract Individuals should alter when they socially associate with conspecifics to avoid potentially costly interactions. Moreover, individuals may vary in their propensity to use information about conspecifics when making such social decisions. However, surprisingly little is known about either the determinants of, or individual variation in, such ‘social plasticity’. We show here that eastern water dragons (Intellegama lesueurii lesueurii) may simultaneously use information from different components of their social environment when deciding whether or not to socially associate. In particular, we found that individuals altered when they socially associated with conspecifics according to the levels of potential conflict and competition in their social environment; both sexes socially associated more at higher local density than would be expected under increased random encounters. Further, females were more likely to socially associate during the breeding season, and when there were more males and/or conspecifics whom they typically avoided in their social environment. This suggests that females may seek safety in numbers when the potential for intra-sexual conflict or sexual harassment is high. Using a behavioral reaction-norm framework, we also provide novel evidence to show that individuals vary in the extent and direction of their social plasticity, and that males varied more than females. Our study thus implies that individuals use multiple cues in their environment when deciding to socially associate, and that the resulting social plasticity varies between the sexes and between individuals. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704089">Read the Article</a></i></p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>ndividuals should alter when they socially associate with conspecifics to avoid potentially costly interactions. Moreover, individuals may vary in their propensity to use information about conspecifics when making such social decisions. However, surprisingly little is known about either the determinants of, or individual variation in, such ‘social plasticity’. We show here that eastern water dragons (<i>Intellegama lesueurii lesueurii</i>) may simultaneously use information from different components of their social environment when deciding whether or not to socially associate. In particular, we found that individuals altered when they socially associated with conspecifics according to the levels of potential conflict and competition in their social environment; both sexes socially associated more at higher local density than would be expected under increased random encounters. Further, females were more likely to socially associate during the breeding season, and when there were more males and/or conspecifics whom they typically avoided in their social environment. This suggests that females may seek safety in numbers when the potential for intra-sexual conflict or sexual harassment is high. Using a behavioral reaction-norm framework, we also provide novel evidence to show that individuals vary in the extent and direction of their social plasticity, and that males varied more than females. Our study thus implies that individuals use multiple cues in their environment when deciding to socially associate, and that the resulting social plasticity varies between the sexes and between individuals.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “A general explanation for the persistence of reproductive interference” https://amnat.org/an/newpapers/AugDrury.html Read the Article Why is reproductive interference so common? A new study suggests animals may be caught in an evolutionary ‘catch-22’ Why do animals sometimes attempt to mate with members of other species, even though doing so is wasteful? A new study by Drury and colleagues offers an answer to this question. Investigators generally assume that wasteful interspecific matings—known as ‘reproductive interference’—will either be eliminated by natural selection or result in one species going locally extinct. Yet, examples of reproductive interference abound, even in species that seem to coexist over long periods of time. In this study, Drury and colleagues argue that such species might be caught in an ‘evolutionary catch-22’. That is, because females of different species often look similar, males are unable to distinguish between females of their own species and females of another species when they come into contact. As a result, natural selection cannot drive divergence in female phenotypes via reproductive character displacement, which requires that males can differentiate between species. Yet, males cannot evolve the ability to differentiate between females until female phenotypes diverge, meaning that reproductive interference persists indefinitely. The study then goes on to demonstrate that the catch-22 explanation is a viable explanation for ongoing reproductive interference in a clade of damselflies distributed throughout North and Central America in which species similarity in female phenotypes predicts levels of reproductive isolation. In particular, they find that in cases where reproductive isolation is high, this isolation cannot be explained by reproductive character displacement, and is better explained by divergence prior to secondary contact. The evolutionary ‘catch-22’ provides a previously undocumented reason why reproductive interference is widespread. Abstract Reproductive interference is widespread, despite the theoretical expectation that it should be eliminated by reproductive character displacement (RCD). A possible explanation is that females of sympatric species are too similar phenotypically for males to distinguish between them, resulting in a type of evolutionary dilemma or “catch-22” in which reproductive interference persists because male mate recognition (MR) cannot evolve until female phenotypes diverge further, and vice versa. Here we illustrate, and test, this hypothesis with data on rubyspot damselflies (Hetaerina spp.). First, reproductive isolation owing to male MR breaks down with increasing interspecific similarity in female phenotypes. Second, comparing allopatric and sympatric populations yielded no evidence for RCD, suggesting that parallel divergence in female coloration and male MR in allopatry determines the level of reproductive isolation upon secondary contact. Whenever reproductive isolation depends on male mate recognition and females of sympatric species are phenotypically similar, the evolutionary catch-22 hypothesis offers an explanation for the persistence of reproductive interference. Una explicación general para la persistencia de la interferencia reproductiva La interferencia reproductiva es común a pesar de la expectativa teórica de que esta debería ser eliminada por el desplazamiento del carácter reproductivo. Una posible explicación sugiere que cuando las hembras de especies simpátricas son muy similares fenotípicamente los machos no pueden distinguir entre ellas, causando así un tipo de dilema evolutivo o “catch-22”. En este caso la interferencia reproductiva persiste debido a que el reconocimiento de pareja por los machos no puede evolucionar hasta cuando se desarrolle una divergencia notoria en el fenotipo de las hembras, y viceversa. En este estudio ilustramos y probamos esta hipótesis con datos obtenidos en libélulas del género Hetaerina spp. Primero, el aislamiento reproductivo debido al reconocimiento de pareja por los machos disminuye con el aumento en la similitud fenotípica interespecífica de las hembras. Segundo, la comparación entre poblaciones alopátricas y simpátricas no mostró evidencia en el desplazamiento del carácter reproductivo. Esto sugiriere que la divergencia paralela en la coloración de las hembras y el reconocimiento de pareja por parte de los machos en alopatría determina el nivel de aislamiento reproductivo al contacto secundario. Cuando las hembras de especies simpátricas son fenotípicamente similares y el aislamiento reproductivo depende del reconocimiento por parte de los machos, la hipótesis evolutiva “catch-22” ofrece una explicación para la persistencia de la interferencia reproductiva. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704102">Read the Article</a></i></p> <p><b>Why is reproductive interference so common? A new study suggests animals may be caught in an evolutionary &lsquo;catch-22&rsquo; </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hy do animals sometimes attempt to mate with members of other species, even though doing so is wasteful? A new study by Drury and colleagues offers an answer to this question. Investigators generally assume that wasteful interspecific matings—known as ‘reproductive interference’—will either be eliminated by natural selection or result in one species going locally extinct. Yet, examples of reproductive interference abound, even in species that seem to coexist over long periods of time. In this study, Drury and colleagues argue that such species might be caught in an ‘evolutionary catch-22’. That is, because females of different species often look similar, males are unable to distinguish between females of their own species and females of another species when they come into contact. As a result, natural selection cannot drive divergence in female phenotypes via reproductive character displacement, which requires that males can differentiate between species. Yet, males cannot evolve the ability to differentiate between females until female phenotypes diverge, meaning that reproductive interference persists indefinitely. The study then goes on to demonstrate that the catch-22 explanation is a viable explanation for ongoing reproductive interference in a clade of damselflies distributed throughout North and Central America in which species similarity in female phenotypes predicts levels of reproductive isolation. In particular, they find that in cases where reproductive isolation is high, this isolation cannot be explained by reproductive character displacement, and is better explained by divergence prior to secondary contact. The evolutionary ‘catch-22’ provides a previously undocumented reason why reproductive interference is widespread.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">R</span>eproductive interference is widespread, despite the theoretical expectation that it should be eliminated by reproductive character displacement (RCD). A possible explanation is that females of sympatric species are too similar phenotypically for males to distinguish between them, resulting in a type of evolutionary dilemma or “catch-22” in which reproductive interference persists because male mate recognition (MR) cannot evolve until female phenotypes diverge further, and vice versa. Here we illustrate, and test, this hypothesis with data on rubyspot damselflies (<i>Hetaerina</i> spp.). First, reproductive isolation owing to male MR breaks down with increasing interspecific similarity in female phenotypes. Second, comparing allopatric and sympatric populations yielded no evidence for RCD, suggesting that parallel divergence in female coloration and male MR in allopatry determines the level of reproductive isolation upon secondary contact. Whenever reproductive isolation depends on male mate recognition and females of sympatric species are phenotypically similar, the evolutionary catch-22 hypothesis offers an explanation for the persistence of reproductive interference. </p> <h4>Una explicación general para la persistencia de la interferencia reproductiva</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>a interferencia reproductiva es común a pesar de la expectativa teórica de que esta debería ser eliminada por el desplazamiento del carácter reproductivo. Una posible explicación sugiere que cuando las hembras de especies simpátricas son muy similares fenotípicamente los machos no pueden distinguir entre ellas, causando así un tipo de dilema evolutivo o “catch-22”. En este caso la interferencia reproductiva persiste debido a que el reconocimiento de pareja por los machos no puede evolucionar hasta cuando se desarrolle una divergencia notoria en el fenotipo de las hembras, y viceversa. En este estudio ilustramos y probamos esta hipótesis con datos obtenidos en libélulas del género <i>Hetaerina</i> spp. Primero, el aislamiento reproductivo debido al reconocimiento de pareja por los machos disminuye con el aumento en la similitud fenotípica interespecífica de las hembras. Segundo, la comparación entre poblaciones alopátricas y simpátricas no mostró evidencia en el desplazamiento del carácter reproductivo. Esto sugiriere que la divergencia paralela en la coloración de las hembras y el reconocimiento de pareja por parte de los machos en alopatría determina el nivel de aislamiento reproductivo al contacto secundario. Cuando las hembras de especies simpátricas son fenotípicamente similares y el aislamiento reproductivo depende del reconocimiento por parte de los machos, la hipótesis evolutiva “catch-22” ofrece una explicación para la persistencia de la interferencia reproductiva. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “Phenotypic diversity arises from secondary signal loss in the elaborate visual displays of toucans and barbets” https://amnat.org/an/newpapers/AugMiles.html Read the Article Secondary loss of signals underlies the evolution of display diversity in toucans The evolution of complexity and diversity are two defining characteristics of life on Earth, but how they relate to each other is still largely a mystery. To address this question, we modeled how a communication system evolved as its individual components were gained and lost throughout evolutionary time. We specifically looked at the visual displays of toucans and barbets, a group of birds found across the continental tropics. Species in the group are mostly known for their big beaks and colorful plumage, but some are a bit more drab. When reading about the birds, we also noticed a common emphasis on tail-based displays. For example, in many species a bird will cock its tail up (and sometimes wave it around) to display, exposing feathers on the rump and undertail. Coincidentally, many species also have contrasting feather patches in the same regions. Some species also ruffle up the rump feathers to display—indeed, including many with a color patch on the rump. Yet others displayed with either gesture (or both) without any special ornaments on the tail. The small number of traits in this system made it perfect for discrete trait modeling, which we used to explore coevolution between gesture and color—and how coevolution influences the evolutionary trajectory toward phenotypic complexity (e.g., a species that has gained many colors and gestures) and diversity (i.e., the range of unique gesture-color combinations present in species today). Indeed, gestures tend to co-evolve with the color patches they emphasize. However, a species with no display whatsoever is only likely to gain a tail-cocking gesture. The chance of gaining a color ornament first was almost zero! Color ornaments were instead gained by lineages that already tail-cock. As a result, we found only a few likely ways that a species’ display evolves from minimum complexity (no gestures, no ornaments) to maximum complexity. Instead, many displays we see today must have evolved as different signal combinations were lost instead: there are only a few ways to become complex, but many routes to diversity. Abstract Complexity and diversity are fundamental characteristics of life, but the relationship between the two remains murky. For example, both gaining and losing complexity can support diversity—so how exactly does complexity influence the emergence of unique phenotypes? Here we address this question by examining how complexity underlies the diversity of elaborate visual displays in an avian clade (Ramphastides, the toucans and barbets). These species communicate in part using body movement and colorful ornaments on the tail. We find that sexual size dimorphism predicts the evolution of one specific signal, the tail-cock gesture, implying that tail-cocking is more likely to evolve under stronger sexual selection. We also discovered process-level constraints on the evolution of complexity: signals are gained along a strict order of operations, where the tail-cock gesture arises before other colors and gestures. Yet virtually any signal can be lost at any time. As a result, many extant phenotypes were more likely to arise through loss of complexity, highlighting the importance of secondary signal loss to phenotypic diversity. Collectively, our results demonstrate how sexual selection catalyzes the evolution of complex phenotypes, which indirectly support diversity by allowing different traits to be modified or lost in the future. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704088">Read the Article</a></i></p> <p><b>Secondary loss of signals underlies the evolution of display diversity in toucans </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he evolution of complexity and diversity are two defining characteristics of life on Earth, but <i>how</i> they relate to each other is still largely a mystery. To address this question, we modeled how a communication system evolved as its individual components were gained and lost throughout evolutionary time. We specifically looked at the visual displays of toucans and barbets, a group of birds found across the continental tropics. Species in the group are mostly known for their big beaks and colorful plumage, but some are a bit more drab. When reading about the birds, we also noticed a common emphasis on tail-based displays. For example, in many species a bird will cock its tail up (and sometimes wave it around) to display, exposing feathers on the rump and undertail. Coincidentally, many species also have contrasting feather patches in the same regions. Some species also ruffle up the rump feathers to display—indeed, including many with a color patch on the rump. Yet others displayed with either gesture (or both) without any special ornaments on the tail. </p><p>The small number of traits in this system made it perfect for discrete trait modeling, which we used to explore coevolution between gesture and color—and how coevolution influences the evolutionary trajectory toward phenotypic complexity (e.g., a species that has gained many colors and gestures) and diversity (i.e., the range of unique gesture-color combinations present in species today). Indeed, gestures tend to co-evolve with the color patches they emphasize. However, a species with no display whatsoever is <i>only likely to gain a tail-cocking gesture</i>. The chance of gaining a color ornament first was almost zero! Color ornaments were instead gained by lineages that already tail-cock. As a result, we found only a few likely ways that a species’ display evolves from minimum complexity (no gestures, no ornaments) to maximum complexity. Instead, many displays we see today must have evolved as different signal combinations were lost instead: there are only a few ways to become complex, but many routes to diversity. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">C</span>omplexity and diversity are fundamental characteristics of life, but the relationship between the two remains murky. For example, both gaining and losing complexity can support diversity—so how exactly does complexity influence the emergence of unique phenotypes? Here we address this question by examining how complexity underlies the diversity of elaborate visual displays in an avian clade (Ramphastides, the toucans and barbets). These species communicate in part using body movement and colorful ornaments on the tail. We find that sexual size dimorphism predicts the evolution of one specific signal, the tail-cock gesture, implying that tail-cocking is more likely to evolve under stronger sexual selection. We also discovered process-level constraints on the evolution of complexity: signals are gained along a strict order of operations, where the tail-cock gesture arises before other colors and gestures. Yet virtually any signal can be lost at any time. As a result, many extant phenotypes were more likely to arise through <i>loss</i> of complexity, highlighting the importance of secondary signal loss to phenotypic diversity. Collectively, our results demonstrate how sexual selection catalyzes the evolution of complex phenotypes, which indirectly support diversity by allowing different traits to be modified or lost in the future. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “Individual and population differences shape species interactions and natural selection” https://amnat.org/an/newpapers/AugStart-A.html Read the Article Small differences among individuals rewire foodwebs and shape natural selection Abstract Trait variation is central to our understanding of species interactions, and trait variation arising within species is increasingly recognized as an important component of community ecology. Ecologists generally consider intraspecific variation either among or within populations, yet these differences can interact to create patterns of species interactions. These differences can also affect species interactions by altering processes occurring at distinct scales. Specifically, intraspecific variation may shape species interactions simply by shifting a population’s position along a trait-function map, or by shifting the relationship between traits and their ecological function. I test these ideas by manipulating within- and among-population intraspecific variation in wild populations of a gall-forming insect, before quantifying species interactions and phenotypic selection. Within- and among-population differences in gall size interact to affect attack rates by an enemy community, but among-population differences were far more consequential. Intraspecific differences shaped species interactions both by shifting the position of populations along the trait-function map, and by altering the relationship between traits and their function, with ultimate consequences for patterns of natural selection. I suggest that intraspecific variation can affect communities and natural selection by acting through individual- and population-level mechanisms. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704060">Read the Article</a></i></p> <p><b>Small differences among individuals rewire foodwebs and shape natural selection </b></p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>rait variation is central to our understanding of species interactions, and trait variation arising within species is increasingly recognized as an important component of community ecology. Ecologists generally consider intraspecific variation either among or within populations, yet these differences can interact to create patterns of species interactions. These differences can also affect species interactions by altering processes occurring at distinct scales. Specifically, intraspecific variation may shape species interactions simply by shifting a population’s position along a trait-function map, or by shifting the relationship between traits and their ecological function. I test these ideas by manipulating within- and among-population intraspecific variation in wild populations of a gall-forming insect, before quantifying species interactions and phenotypic selection. Within- and among-population differences in gall size interact to affect attack rates by an enemy community, but among-population differences were far more consequential. Intraspecific differences shaped species interactions both by shifting the position of populations along the trait-function map, and by altering the relationship between traits and their function, with ultimate consequences for patterns of natural selection. I suggest that intraspecific variation can affect communities and natural selection by acting through individual- and population-level mechanisms. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT “Nineteen years of consistently positive and strong female mate preferences despite individual variation” https://amnat.org/an/newpapers/AugRyan.html Read the ArticleFemale mate choice generates some of the most spectacular biological diversity in the animal kingdom. Or does it? Alfred Wallace was no supporter of Darwin’s sexual selection theory because he could not imagine females showing persistent preferences for the same details of sexual beauty over generations. Julian Huxley, another critic, voiced some similar concerns. For female choice to be an important driver of sexual beauty, it has been argued, it must be strong and it must be consistent—fickle preferences won’t cut it. Amazingly, there are very few studies of female mate choice across a substantial number of generations. A group of researchers has been studying sexual selection in túngara frogs in Panama for several decades. Although the foci of this research program are varied, the hallmark has been the female’s preference for complex calls over simple calls. Simple calls are adequate to attract a mate but complex calls are preferred. But is this preference strong and consistent? Nineteen consecutive years of more than 5000 female mate choice tests have shown an average preference for the complex call of 0.86—more than a five-fold preference! Clearly it is strong, but is it consistent? Yes. There is very little variation in this strength of preference across years. Does this consistency across years mean there is similar consistency among females? No. Although most females have strong preferences for the complex call there is significant variation amongst females within years, much more so than the variation among years. Although other female preferences in this frog and female preferences in other species are known to be fickle, the preference for complex calls is strong and consistent just as Darwin suggested when he posited that females have a taste for the beautiful. Abstract Sexual selection driven by mate choice has generated some of the most astounding diversity in nature, suggesting population-level preferences should be strong and consistent over many generations. On the other hand, mating preferences are among the least repeatable components of an individual animal’s phenotype, suggesting low consistency across an animal’s lifetime. Despite decades of intensive study of sexual selection there is almost no information about the strength and consistency of preferences across many years. In this study we present the results of over 5000 mate choice tests with a species of wild frog conducted over 19 consecutive years. Results show that preferences are positive and strong and vary little across years. This consistency is despite the fact that there are substantial differences among females in their strength of preference. We also suggest mate preferences in populations that are primarily the result of sensory exploitation might be more stable over time compared to preferences that are primarily involved in assessing male quality. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/704103">Read the Article</a></i></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">F</span>emale mate choice generates some of the most spectacular biological diversity in the animal kingdom. Or does it? Alfred Wallace was no supporter of Darwin’s sexual selection theory because he could not imagine females showing persistent preferences for the same details of sexual beauty over generations. Julian Huxley, another critic, voiced some similar concerns. For female choice to be an important driver of sexual beauty, it has been argued, it must be strong and it must be consistent—fickle preferences won’t cut it. Amazingly, there are very few studies of female mate choice across a substantial number of generations.</p> <p>A group of researchers has been studying sexual selection in túngara frogs in Panama for several decades. Although the foci of this research program are varied, the hallmark has been the female’s preference for complex calls over simple calls. Simple calls are adequate to attract a mate but complex calls are preferred. But is this preference strong and consistent? Nineteen consecutive years of more than 5000 female mate choice tests have shown an average preference for the complex call of 0.86—more than a five-fold preference! Clearly it is strong, but is it consistent? Yes. There is very little variation in this strength of preference across years. Does this consistency across years mean there is similar consistency among females? No. Although most females have strong preferences for the complex call there is significant variation amongst females within years, much more so than the variation among years. Although other female preferences in this frog and female preferences in other species are known to be fickle, the preference for complex calls is strong and consistent just as Darwin suggested when he posited that females have a <i>taste for the beautiful</i>.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>exual selection driven by mate choice has generated some of the most astounding diversity in nature, suggesting population-level preferences should be strong and consistent over many generations. On the other hand, mating preferences are among the least repeatable components of an individual animal’s phenotype, suggesting low consistency across an animal’s lifetime. Despite decades of intensive study of sexual selection there is almost no information about the strength and consistency of preferences across many years. In this study we present the results of over 5000 mate choice tests with a species of wild frog conducted over 19 consecutive years. Results show that preferences are positive and strong and vary little across years. This consistency is despite the fact that there are substantial differences among females in their strength of preference. We also suggest mate preferences in populations that are primarily the result of sensory exploitation might be more stable over time compared to preferences that are primarily involved in assessing male quality. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 23 Apr 2019 05:00:00 GMT