ASN RSS http://amnat.org/ Latest press releases and announcements from the ASN en-us Sun, 17 Jun 2018 05:00:00 GMT 60 “Introgression across hybrid zones is not mediated by Large X-effects in green toads with undifferentiated sex chromosomes” http://amnat.org/an/newpapers/NovGerchen-A.html Abstract Divergence between incipient species remains an incompletely understood process. Hybrid zones provide great research potential, reflecting natural organismal genomic interactions and gene evolution in a variety of recombinants over generations. While sex chromosomes are known evolutionary drivers of reproductive isolation, empirical population genetics mostly examined species with heteromorphic sex chromosomes. We recently reported restricted introgression at sex-linked markers in an amphibian system with homomorphic sex chromosomes (Hyla), consistent with a Large X-effect, designating a greater role of sex chromosomes in driving hybrid incompatibilities. Here, using a similar approach, we examined two hybrid zones of Palearctic green toads (Bufo viridis subgroup), involving several lineages that arose at different times and form secondary contacts. We find no evidence for differential introgression of sex-linked vs. autosomal markers across both zones. This absence of Large X-effects in Bufo indicates that, unlike in Hyla, hybrid incompatibilities may not result from faster-heterogametic sex and faster-male aspects of Haldane’s rule. The recent suppression of XY recombination in Hyla, but not in Bufo, may have driven greater divergence between Hyla sex chromosomes, causing stronger reproductive isolation. Alternatively, stronger linkage among Hyla’s sex-linked markers could restrict introgression. We hypothesize that the degree of sex-specific recombination may condition the importance of homomorphic sex chromosomes in speciation. More forthcoming papers &raquo; <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>ivergence between incipient species remains an incompletely understood process. Hybrid zones provide great research potential, reflecting natural organismal genomic interactions and gene evolution in a variety of recombinants over generations. While sex chromosomes are known evolutionary drivers of reproductive isolation, empirical population genetics mostly examined species with heteromorphic sex chromosomes. We recently reported restricted introgression at sex-linked markers in an amphibian system with homomorphic sex chromosomes (<i>Hyla</i>), consistent with a Large X-effect, designating a greater role of sex chromosomes in driving hybrid incompatibilities. Here, using a similar approach, we examined two hybrid zones of Palearctic green toads (<i>Bufo viridis</i> subgroup), involving several lineages that arose at different times and form secondary contacts. We find no evidence for differential introgression of sex-linked vs. autosomal markers across both zones. This absence of Large X-effects in <i>Bufo</i> indicates that, unlike in <i>Hyla</i>, hybrid incompatibilities may not result from <i>faster-heterogametic sex</i> and <i>faster-male</i> aspects of Haldane’s rule. The recent suppression of XY recombination in <i>Hyla</i>, but not in <i>Bufo</i>, may have driven greater divergence between <i>Hyla</i> sex chromosomes, causing stronger reproductive isolation. Alternatively, stronger linkage among <i>Hyla</i>’s sex-linked markers could restrict introgression. We hypothesize that the degree of sex-specific recombination may condition the importance of homomorphic sex chromosomes in speciation. </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, 11 Jun 2018 05:00:00 GMT “Collective action promoted by key individuals” http://amnat.org/an/newpapers/OctWheatcroft.html The DOI will be https://dx.doi.org/10.1086/698874 High-gain individuals help form cooperative groups by incentivizing low-gain individuals to join A&nbsp;farmer rushes out of her house to confront a bear raiding her crops. She is soon followed by her neighbor, and together they succeed in scaring the bear away. The next day, the farmer is at the market when the bear comes again. This time, the bear has a feast while the neighbor watches on. Why might the neighbor join with another to perform an action she would not do on her own, especially given she would also benefit if the bear is driven away from the general vicinity? Complicated explanations, such as that of reciprocal altruism (“I help you now in the expectation you will help me later”) prevail in the literature. A simpler one comes with two conditions. First, the benefits should outweigh the costs for some individuals (i.e., the farmer) who perform the behavior even when alone. Second, once one individual is performing the behavior, the costs for others (i.e., the neighbor) are sufficiently reduced so that they are outweighed by the benefits. David Wheatcroft and Trevor Price asked if this idea can explain cooperative behaviors in nature. They studied responses of small birds to various enemies over four years in the western Himalayas. Crows prey upon the eggs and chicks of small birds, and cuckoos parasitize their nests. Wheatcroft and Price used taxidermied mounts of crows and cuckoos to show that, when acting alone, the only individuals to strongly attack the mounts were those with nests nearby. As long as nest owners are present, birds without nearby nests also join. By contrast, hawk and owl mounts are always vigorously attacked. Wheatcroft and Price then developed a theory of changing cost:benefit relationships, assuming the principles outlined above apply. They show that the results are as expected if crows and cuckoos are not too costly to attack and costs decline with the number of birds attacking the mount, but benefits always accrue to individuals attacking hawks and owls. Simple mechanisms (i.e., join if you benefit) may regularly explain the formation of cooperative groups. Abstract Explaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (“mobs”) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of Phylloscopus warblers. Even when alone, birds are aggressive towards predators of adult birds, both at and away from their nests. By contrast, birds aggressively confront nest threats alone only when they have a nest nearby. However, strong initial responses by nest owners lead individuals without nearby nests to increase their responses, thereby generating a mob. Building on these findings, we derive the conditions when individuals are incentivized to invest more when joining a high-gain individual compared to when acting alone. Strong responses of high-gain individuals acting alone tend to reduce the investments of other high-gain individuals that subsequently join. However, individuals that benefit sufficiently little from acting alone increase their investments when joining a high-gain individual and can even be sufficiently incentivized to join in when they would otherwise not act alone. Together, these results suggest an important role for key individuals in the generation of some group behaviors. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698874 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698874">Read the Article</a></i> </p> --> <p><b>High-gain individuals help form cooperative groups by incentivizing low-gain individuals to join </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>&nbsp;farmer rushes out of her house to confront a bear raiding her crops. She is soon followed by her neighbor, and together they succeed in scaring the bear away. The next day, the farmer is at the market when the bear comes again. This time, the bear has a feast while the neighbor watches on. Why might the neighbor join with another to perform an action she would not do on her own, especially given she would also benefit if the bear is driven away from the general vicinity? Complicated explanations, such as that of reciprocal altruism (“I help you now in the expectation you will help me later”) prevail in the literature. A simpler one comes with two conditions. First, the benefits should outweigh the costs for some individuals (i.e., the farmer) who perform the behavior even when alone. Second, once one individual is performing the behavior, the costs for others (i.e., the neighbor) are sufficiently reduced so that they are outweighed by the benefits. </p><p>David Wheatcroft and Trevor Price asked if this idea can explain cooperative behaviors in nature. They studied responses of small birds to various enemies over four years in the western Himalayas. Crows prey upon the eggs and chicks of small birds, and cuckoos parasitize their nests. Wheatcroft and Price used taxidermied mounts of crows and cuckoos to show that, when acting alone, the only individuals to strongly attack the mounts were those with nests nearby. As long as nest owners are present, birds without nearby nests also join. By contrast, hawk and owl mounts are always vigorously attacked. Wheatcroft and Price then developed a theory of changing cost:benefit relationships, assuming the principles outlined above apply. They show that the results are as expected if crows and cuckoos are not too costly to attack and costs decline with the number of birds attacking the mount, but benefits always accrue to individuals attacking hawks and owls. Simple mechanisms (i.e., join if you benefit) may regularly explain the formation of cooperative groups. </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;">E</span>xplaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (“mobs”) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of <i>Phylloscopus</i> warblers. Even when alone, birds are aggressive towards predators of adult birds, both at and away from their nests. By contrast, birds aggressively confront nest threats alone only when they have a nest nearby. However, strong initial responses by nest owners lead individuals without nearby nests to increase their responses, thereby generating a mob. Building on these findings, we derive the conditions when individuals are incentivized to invest more when joining a high-gain individual compared to when acting alone. Strong responses of high-gain individuals acting alone tend to reduce the investments of other high-gain individuals that subsequently join. However, individuals that benefit sufficiently little from acting alone increase their investments when joining a high-gain individual and can even be sufficiently incentivized to join in when they would otherwise not act alone. Together, these results suggest an important role for key individuals in the generation of some group behaviors. </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, 05 Jun 2018 05:00:00 GMT “Gene-culture co-inheritance of a behavioral trait” http://amnat.org/an/newpapers/SepAguilar-A.html The DOI will be https://dx.doi.org/10.1086/698872 Gene-Culture Price equation shows when cultural selection beats genetic selection Abstract Many physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems, and their interaction, in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive. We then use this equation to investigate whether a genetically maladaptive phenotype can evolve under dual transmission. We examine the special case of altruism using an illustrative model, and show that cultural selection can overcome genetic selection when the variance in culture is sufficiently high with respect to genes. We also show that the presence of cultural transmission can modify genetic selection itself, making genetic selection more favorable to a trait than under purely genetic inheritance. Lastly, we consider the effect of different timescales of genetic and cultural transmission. We discuss the implications of our results for understanding the evolution of important co-inherited behaviors, including how our framework can be used to generate quantitative estimates of selection pressures required for a genetically maladaptive trait to evolve. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698872 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698872">Read the Article</a></i> </p> --> <p><b>Gene-Culture Price equation shows when cultural selection beats genetic 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;">M</span>any physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems, and their interaction, in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive. We then use this equation to investigate whether a genetically maladaptive phenotype can evolve under dual transmission. We examine the special case of altruism using an illustrative model, and show that cultural selection can overcome genetic selection when the variance in culture is sufficiently high with respect to genes. We also show that the presence of cultural transmission can modify genetic selection itself, making genetic selection more favorable to a trait than under purely genetic inheritance. Lastly, we consider the effect of different timescales of genetic and cultural transmission. We discuss the implications of our results for understanding the evolution of important co-inherited behaviors, including how our framework can be used to generate quantitative estimates of selection pressures required for a genetically maladaptive trait to evolve. </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, 05 Jun 2018 05:00:00 GMT “Fitness consequences of interspecific nesting associations among cavity nesting birds” http://amnat.org/an/newpapers/SepMouton.html The DOI will be https://dx.doi.org/10.1086/698873 Nest tree availability and nest predation risk affect the benefits and rate of nest tree sharing in cavity nesting birds Some of the most visually striking and exciting sights in nature are large herds, flocks, schools, and colonies of animals. Animals may benefit from being in a group with other species because it can reduce their chances of being killed by a predator, but on the other hand, large groups can attract predators. Competition over resources (i.e. food or breeding sites) between similar species can also cause fighting within the group making it difficult for groups to form. This suggests that similar species that often fight should keep their distance and not form groups. However, birds that nest in holes in trees (cavity nesters) are well known for aggressively attacking one another, especially around nests, can be seen sometimes nesting together in the same tree. How commonly does this occur? Why do they share nest trees in the first place? James Mouton and Tom Martin set out to answer these questions by looking at whether the number of nests sharing trees changed in years with different availability of nest sites and risk that a predator eats the eggs or offspring). They found that sharing nest trees was more common in years with more nest trees and in years with higher risk of nest predation. They also found that nests in shared trees were less likely to be depredated than solitary nests, but only in years with high risk of predation. Together, these findings suggest that birds may fight less when nest sites are abundant, allowing them to nest close together more often and that birds may nest close together even when then fight if predation risk is especially high. Still, experiments are needed to fully understand these patterns. Ultimately, it seems that even though they are known for fighting, cavity nesting birds tolerate nesting together in the right conditions. Abstract Interspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet, tests of such possibilities are lacking. Cavity nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but we found they commonly aggregate by sharing nest trees across 19 years of study. Tree sharing was more common when aspen were more abundant and somewhat more common in years with higher nest predation risk. Nest success was higher in shared trees when nest predation risk was higher than average. Ultimately, the costs and benefits of aggregating (nest tree sharing) varied across years and we outline hypotheses for future studies. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698873 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698873">Read the Article</a></i> </p> --> <p><b>Nest tree availability and nest predation risk affect the benefits and rate of nest tree sharing in cavity nesting birds </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>ome of the most visually striking and exciting sights in nature are large herds, flocks, schools, and colonies of animals. Animals may benefit from being in a group with other species because it can reduce their chances of being killed by a predator, but on the other hand, large groups can attract predators. Competition over resources (i.e. food or breeding sites) between similar species can also cause fighting within the group making it difficult for groups to form. This suggests that similar species that often fight should keep their distance and not form groups. However, birds that nest in holes in trees (cavity nesters) are well known for aggressively attacking one another, especially around nests, can be seen sometimes nesting together in the same tree. How commonly does this occur? Why do they share nest trees in the first place? </p><p>James Mouton and Tom Martin set out to answer these questions by looking at whether the number of nests sharing trees changed in years with different availability of nest sites and risk that a predator eats the eggs or offspring). They found that sharing nest trees was more common in years with more nest trees and in years with higher risk of nest predation. They also found that nests in shared trees were less likely to be depredated than solitary nests, but only in years with high risk of predation. Together, these findings suggest that birds may fight less when nest sites are abundant, allowing them to nest close together more often and that birds may nest close together even when then fight if predation risk is especially high. Still, experiments are needed to fully understand these patterns. Ultimately, it seems that even though they are known for fighting, cavity nesting birds tolerate nesting together in the right conditions. </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>nterspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet, tests of such possibilities are lacking. Cavity nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but we found they commonly aggregate by sharing nest trees across 19 years of study. Tree sharing was more common when aspen were more abundant and somewhat more common in years with higher nest predation risk. Nest success was higher in shared trees when nest predation risk was higher than average. Ultimately, the costs and benefits of aggregating (nest tree sharing) varied across years and we outline hypotheses for future studies. </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, 05 Jun 2018 05:00:00 GMT “Female life history trade-offs and the maintenance of genetic variation in Drosophila melanogaster” http://amnat.org/an/newpapers/OctArbuthnott.html The DOI will be https://dx.doi.org/10.1086/698727 Many processes and trade-offs work together to weaken selection, allowing populations to maintain genetic diversity Why do we see so much variation within species, with individuals differing widely in traits that affect fitness? Natural and sexual selection should favour advantageous traits, and populations should become more homogeneous as selection increases the frequency of these traits. Yet substantial variation is observed in fitness-related traits in a wide variety of species. In this study, Arbuthnott tests a number of alternate hypotheses as to how variation is maintained using inbred lines of fruit flies. From dozens of trait measurements and experiments, the author finds that no one mechanism is strong enough to counteract selection and maintain variation on its own. However, the author finds a number of weak genetic correlations and trade-offs between different fitness-related traits, and suggests that several mechanisms may each weaken selection incrementally. When these weakening mechanisms are combined, they may act to slow the purging of disadvantageous traits, and maintain genetic variation within populations. This comprehensive study is the first to suggest that many weak processes may act together to maintain variation, which may have important implications for our understanding of genetic diversity and evolution. Abstract Why do we observe substantial variation in fitness-related traits under strong natural or sexual selection? While there is support for several selective and neutral mechanisms acting in select systems, we lack a comprehensive analysis of the relative importance of various mechanisms within a single system. Furthermore, while sexually selected male traits have been a central focus of this paradox, female sexual traits have rarely been considered. In this study, I evaluate the contribution of various selective mechanisms towards the maintenance of substantial variation in female attractiveness and offspring production observed among Drosophila melanogaster genotypes. I tested for contributions from antagonistic pleiotropy, frequency-dependent selection, changing environments, and sexual conflict. I found negative genetic correlations between some traits (male attractiveness vs. female resistance to male harm, early offspring production and reproductive senescence), and genotype-specific changes in fitness between environments. However, no measurement found strong trade-offs among the fitness components of these genotypes. Overall, I find little evidence that any one mechanism is strong enough to maintain genetic variation on its own. Instead, I suggest that many mechanisms may weaken the selection among genotypes, which would collectively allow neutral processes such as mutation-selection balance to maintain genetic variation within populations. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698727 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698727">Read the Article</a></i> </p> --> <p><b>Many processes and trade-offs work together to weaken selection, allowing populations to maintain genetic diversity </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;">W</span>hy do we see so much variation within species, with individuals differing widely in traits that affect fitness? Natural and sexual selection should favour advantageous traits, and populations should become more homogeneous as selection increases the frequency of these traits. Yet substantial variation is observed in fitness-related traits in a wide variety of species. In this study, Arbuthnott tests a number of alternate hypotheses as to how variation is maintained using inbred lines of fruit flies. From dozens of trait measurements and experiments, the author finds that no one mechanism is strong enough to counteract selection and maintain variation on its own. However, the author finds a number of weak genetic correlations and trade-offs between different fitness-related traits, and suggests that several mechanisms may each weaken selection incrementally. When these weakening mechanisms are combined, they may act to slow the purging of disadvantageous traits, and maintain genetic variation within populations. This comprehensive study is the first to suggest that many weak processes may act together to maintain variation, which may have important implications for our understanding of genetic diversity and evolution.</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;">W</span>hy do we observe substantial variation in fitness-related traits under strong natural or sexual selection? While there is support for several selective and neutral mechanisms acting in select systems, we lack a comprehensive analysis of the relative importance of various mechanisms within a single system. Furthermore, while sexually selected male traits have been a central focus of this paradox, female sexual traits have rarely been considered. In this study, I evaluate the contribution of various selective mechanisms towards the maintenance of substantial variation in female attractiveness and offspring production observed among <i>Drosophila melanogaster</i> genotypes. I tested for contributions from antagonistic pleiotropy, frequency-dependent selection, changing environments, and sexual conflict. I found negative genetic correlations between some traits (male attractiveness vs. female resistance to male harm, early offspring production and reproductive senescence), and genotype-specific changes in fitness between environments. However, no measurement found strong trade-offs among the fitness components of these genotypes. Overall, I find little evidence that any one mechanism is strong enough to maintain genetic variation on its own. Instead, I suggest that many mechanisms may weaken the selection among genotypes, which would collectively allow neutral processes such as mutation-selection balance to maintain genetic variation within populations.</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, 30 May 2018 05:00:00 GMT “Prey limitation drives variation in allometric scaling of predator-prey interactions” http://amnat.org/an/newpapers/OctCostaP.html The DOI will be https://dx.doi.org/10.1086/698726 Variation in allometric scaling of predator-prey interactions is predicted by gradients of prey limitation Predators should carefully choose their prey. Small-sized prey may be tricky to find and capture, and usually have low energetic return. In turn, too large prey are difficult to overcome, subdue, and even ingest. Therefore, foraging theories predict an intermediate optimal relative size-difference between predators and their prey. Although this theoretical concept has been widely used to model the dynamics and structure of predator-prey populations and food webs, empirical systems show a tremendous variation in predator-prey size ratios. To investigate the underlying causes of this unexpected variation, the authors analyzed more than 6,000 trophic interactions between tropical frog species and their prey across a diverse range of communities in the Pantanal wetlands of Brazil. Surprisingly, they demonstrated that variation in the relative size of predators and their prey is not simply “noise” but instead can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. Importantly, this study shows for the first time that the variance of size-scaling ratios is neither negligible nor constant as currently assumed, but instead it changes predictably across communities. This variation has important consequences for ecological and evolutionary dynamics of food webs. Together, these findings make clear that prey limitation leads to deviations from the universal size-scaling constant and thus challenges current paradigms of metabolic and food web theories. Abstract Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, Predator-Prey Size Ratios (PPSR) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here, we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. We analyzed >6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size-dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.A limitação de presas explica a variação na alometria de interações predador-presa Ecólogos têm buscado há muito tempo uma constante alométrica universal que governe relações tróficas. Embora esse seja um conceito teórico atraente, razões de tamanho predador-presa (PPSR) variam amplamente entre e dentro de teias tróficas naturais, o que indica que predadores desviam de seus tamanhos ótimos de presa consumindo recursos relativamente maiores ou menores. Aqui, nós sugerimos que essa inesperada variação alométrica em interações tróficas pode ser predita por gradientes de limitação de presas, o que seria consistente com a Teoria do Forrageamento Ótimo. Nós analisamos >6.000 interações tróficas em 52 populações de quatro espécies de rãs tropicais ao longo de um gradiente de limitação de presas. A PPSR média e sua variância diferiram até duas ordens de magnitude entre e dentro das teias tróficas. Particularmente, conforme a disponibilidade de presas diminuiu nas teias tróficas, a PPSR e sua variância se tornaram mais dependentes do tamanho corpóreo dos predadores. Desse modo, interações tróficas não seguem uma constante alométrica fixa, mas variam previsivelmente de acordo com a magnitude da limitação de presas. Nossos resultados enfatizam a importância de diferentes contextos ecológicos no arranjo de teias tróficas e a necessidade de incorporar os mecanismos ecológicos que afetam a PPSR e sua variância em modelos de teias tróficas e comunidades. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698726 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698726">Read the Article</a></i> </p> --> <p><b>Variation in allometric scaling of predator-prey interactions is predicted by gradients of prey limitation </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>redators should carefully choose their prey. Small-sized prey may be tricky to find and capture, and usually have low energetic return. In turn, too large prey are difficult to overcome, subdue, and even ingest. Therefore, foraging theories predict an intermediate optimal relative size-difference between predators and their prey. Although this theoretical concept has been widely used to model the dynamics and structure of predator-prey populations and food webs, empirical systems show a tremendous variation in predator-prey size ratios. </p><p>To investigate the underlying causes of this unexpected variation, the authors analyzed more than 6,000 trophic interactions between tropical frog species and their prey across a diverse range of communities in the Pantanal wetlands of Brazil. Surprisingly, they demonstrated that variation in the relative size of predators and their prey is not simply &ldquo;noise&rdquo; but instead can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. Importantly, this study shows for the first time that the variance of size-scaling ratios is neither negligible nor constant as currently assumed, but instead it changes predictably across communities. This variation has important consequences for ecological and evolutionary dynamics of food webs. Together, these findings make clear that prey limitation leads to deviations from the universal size-scaling constant and thus challenges current paradigms of metabolic and food web theories.</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;">E</span>cologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, Predator-Prey Size Ratios (PPSR) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here, we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. We analyzed &gt;6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size-dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.</p><h4>A limitação de presas explica a variação na alometria de interações predador-presa</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;">E</span>cólogos têm buscado há muito tempo uma constante alométrica universal que governe relações tróficas. Embora esse seja um conceito teórico atraente, razões de tamanho predador-presa (PPSR) variam amplamente entre e dentro de teias tróficas naturais, o que indica que predadores desviam de seus tamanhos ótimos de presa consumindo recursos relativamente maiores ou menores. Aqui, nós sugerimos que essa inesperada variação alométrica em interações tróficas pode ser predita por gradientes de limitação de presas, o que seria consistente com a Teoria do Forrageamento Ótimo. Nós analisamos >6.000 interações tróficas em 52 populações de quatro espécies de rãs tropicais ao longo de um gradiente de limitação de presas. A PPSR média e sua variância diferiram até duas ordens de magnitude entre e dentro das teias tróficas. Particularmente, conforme a disponibilidade de presas diminuiu nas teias tróficas, a PPSR e sua variância se tornaram mais dependentes do tamanho corpóreo dos predadores. Desse modo, interações tróficas não seguem uma constante alométrica fixa, mas variam previsivelmente de acordo com a magnitude da limitação de presas. Nossos resultados enfatizam a importância de diferentes contextos ecológicos no arranjo de teias tróficas e a necessidade de incorporar os mecanismos ecológicos que afetam a PPSR e sua variância em modelos de teias tróficas e comunidades. </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, 23 May 2018 05:00:00 GMT “The energetic cost of reproduction and its effect on optimal life-history strategies” http://amnat.org/an/newpapers/OctAudzijonyte.html The DOI will be https://dx.doi.org/10.1086/698655 A model with energetic and size specific reproduction cost provides new explanation for the importance of large fish Why do some animals delay reproduction when this entails the risk of not leaving any progeny at all? Attempts to answer this question have motivated the development of life-history theory that aims to understand key determinants of maturation size and reproductive effort. Asta Audzijonyte and Shane Richards suggest that the energetic cost of reproduction, while often ignored or treated implicitly in life-history models, can be substantial and will influence optimal timing of reproduction events. Audzijonyte and Richards present a life-history model that assumes that reproduction requires a minimum energy pool to cover the costs of reproductive behavior, such as mating, migration, or parental care. The researchers propose that for indeterminate growers, such as fish, this energetic cost of reproduction likely scales sublinearly with size, which implies that reproduction is relatively cheaper for larger individuals. Decreasing relative cost of reproduction with size means that delayed reproduction can be an optimal reproductive strategy and that relative reproductive output increases with size. Importantly, the energetic cost of reproduction sets limits on the smallest viable maturation size, which constrains a population’s ability to adapt to size-dependent and human-induced mortality, such as fishing. Audzijonyte and Richards suggest that the scaling of the reproduction cost with body size is a fundamental species’ parameter that allows for dynamically emergent maturation size and explains skipped reproduction events and high fitness of large individuals. Abstract Trade-offs in energy allocation between growth, reproduction and survival are at the core of life-history theory. While age-specific mortality is considered to be the main determinant of the optimal allocation, some life-history strategies, such as delayed or skipped reproduction may be better understood when also accounting for reproduction costs. Here, we present a two-pool indeterminate grower model that includes a survival and energetic cost of reproduction. The energetic cost sets a minimum reserve required for reproduction, while survival cost reflects increased mortality from low post-reproductive body condition. Three life-history parameters determining age-dependent energy allocation to soma, reserve and reproduction are optimized, and we show that the optimal strategies can reproduce realistic emergent growth trajectories, maturation ages and reproductive outputs for fish. The model predicts maturation phase shifts along the gradient of condition related mortality and shows that increased harvesting will select for earlier maturation and higher energy allocation to reproduction. However, since the energetic reproduction cost sets limits on how early an individual can mature, increase in fitness at high harvesting can only be achieved by diverting most reserve into reproduction. The model presented here can improve predictions of life-history responses to environmental change and human impacts because key life-history traits such as maturation age and size, maximum body size, and size-specific fecundity emerge dynamically. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698655 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698655">Read the Article</a></i> </p> --> <p><b>A model with energetic and size specific reproduction cost provides new explanation for the importance of large fish </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 some animals delay reproduction when this entails the risk of not leaving any progeny at all? Attempts to answer this question have motivated the development of life-history theory that aims to understand key determinants of maturation size and reproductive effort. Asta Audzijonyte and Shane Richards suggest that the energetic cost of reproduction, while often ignored or treated implicitly in life-history models, can be substantial and will influence optimal timing of reproduction events. </p><p>Audzijonyte and Richards present a life-history model that assumes that reproduction requires a minimum energy pool to cover the costs of reproductive behavior, such as mating, migration, or parental care. The researchers propose that for indeterminate growers, such as fish, this energetic cost of reproduction likely scales sublinearly with size, which implies that reproduction is relatively cheaper for larger individuals. Decreasing relative cost of reproduction with size means that delayed reproduction can be an optimal reproductive strategy and that relative reproductive output increases with size. Importantly, the energetic cost of reproduction sets limits on the smallest viable maturation size, which constrains a population’s ability to adapt to size-dependent and human-induced mortality, such as fishing. Audzijonyte and Richards suggest that the scaling of the reproduction cost with body size is a fundamental species’ parameter that allows for dynamically emergent maturation size and explains skipped reproduction events and high fitness of large individuals. </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>rade-offs in energy allocation between growth, reproduction and survival are at the core of life-history theory. While age-specific mortality is considered to be the main determinant of the optimal allocation, some life-history strategies, such as delayed or skipped reproduction may be better understood when also accounting for reproduction costs. Here, we present a two-pool indeterminate grower model that includes a survival and energetic cost of reproduction. The energetic cost sets a minimum reserve required for reproduction, while survival cost reflects increased mortality from low post-reproductive body condition. Three life-history parameters determining age-dependent energy allocation to soma, reserve and reproduction are optimized, and we show that the optimal strategies can reproduce realistic emergent growth trajectories, maturation ages and reproductive outputs for fish. The model predicts maturation phase shifts along the gradient of condition related mortality and shows that increased harvesting will select for earlier maturation and higher energy allocation to reproduction. However, since the energetic reproduction cost sets limits on how early an individual can mature, increase in fitness at high harvesting can only be achieved by diverting most reserve into reproduction. The model presented here can improve predictions of life-history responses to environmental change and human impacts because key life-history traits such as maturation age and size, maximum body size, and size-specific fecundity emerge dynamically. </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, 09 May 2018 05:00:00 GMT “Extreme insolation: climatic variation shapes the evolution of thermal tolerance at multiple scales” http://amnat.org/an/newpapers/SepBaudier.html The DOI will be https://dx.doi.org/10.1086/698656 Insolation predicts thermal tolerance from microclimate to elevational clines Most tests of animal adaptation to local thermal environments use correlations of thermal physiology with local mean temperatures across latitudes or over elevation gradients. Such approaches ignore potentially important sources of ambient temperature variation, introducing confounds and potentially complicating interpretation of the geography of thermal adaptation. Baudier and co-authors in the O’Donnell Lab at Drexel University conducted a study to test whether temperature extremes or temperature means are a bigger factor in the evolution of thermal tolerance limits. This within-latitude comparative study of Costa Rican army ants’ insolation adaptations examined multiple scales of thermal variation: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats. Baudier and co-authors found that thermally-buffered subterranean species had narrower thermal tolerance ranges compared to surface-active species, and also found that the relationship between heat tolerance and elevation differed by species surface activity level: heat tolerance decreased with elevation for subterranean species, but heat tolerance didn’t differ across elevations for above-ground species. The relationship between cold tolerance and elevation did not differ across species microhabitat use. Greater seasonal temperature variation in dry forests caused improved heat tolerance but did not affect cold tolerance. These patterns suggest that upper and lower thermal tolerances respond to different selective pressures in the environment. Heat tolerance likely evolves under selection from extreme warming events more than mean temperature, and cold tolerance in the tropics seems to be more selected for by mean annual temperature. Extreme heat spikes are predicted to become more common because of anthropogenic climate change. These changes may have most dangerous consequences for tropical species adapted to historically stable conditions. Abstract The climatic variability hypothesis (CVH) is a cornerstone of thermal ecology, predicting the evolution of wider organismal thermal tolerance ranges in more thermally variable environments. Thermal tolerance ranges depend on both upper and lower tolerance limits (critical thermal maxima: CTmax, and critical thermal minima: CTmin), which may show different responses to environmental gradients. To delineate the relative effects of mean and extreme temperatures on thermal tolerances, we conducted a within-latitude comparative test of CVH predictions for army ants (Dorylinae) at multiple scales: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats. Consistent with the CVH, thermally-buffered subterranean species had narrower thermal tolerance ranges. Both CTmin and CTmax decreased with elevation for subterranean species. In contrast, aboveground species (those exposed to insolation) showed a decrease in CTmin but no change in CTmax across elevations. Furthermore, greater seasonal temperature variation in dry forests correlated with increased CTmax, but not CTmin These patterns suggest CTmax and CTmin respond to different abiotic selective forces: habitat-specific exposure to extreme insolation corresponds to CTmax differences, but not to CTmin variation. We predict increasingly frequent heat spikes associated with climate change will have habitat-specific physiological consequences for ectothermic animals. Models predicting climate change impacts should account for species microhabitat uses and within-latitude differences in temperature seasonality. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698656 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698656">Read the Article</a></i> </p> --> <p><b>Insolation predicts thermal tolerance from microclimate to elevational clines </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>ost tests of animal adaptation to local thermal environments use correlations of thermal physiology with local mean temperatures across latitudes or over elevation gradients. Such approaches ignore potentially important sources of ambient temperature variation, introducing confounds and potentially complicating interpretation of the geography of thermal adaptation. Baudier and co-authors in the O’Donnell Lab at Drexel University conducted a study to test whether temperature extremes or temperature means are a bigger factor in the evolution of thermal tolerance limits. This within-latitude comparative study of Costa Rican army ants’ insolation adaptations examined multiple scales of thermal variation: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats. </p><p>Baudier and co-authors found that thermally-buffered subterranean species had narrower thermal tolerance ranges compared to surface-active species, and also found that the relationship between heat tolerance and elevation differed by species surface activity level: heat tolerance decreased with elevation for subterranean species, but heat tolerance didn’t differ across elevations for above-ground species. The relationship between cold tolerance and elevation did not differ across species microhabitat use. Greater seasonal temperature variation in dry forests caused improved heat tolerance but did not affect cold tolerance. These patterns suggest that upper and lower thermal tolerances respond to different selective pressures in the environment. Heat tolerance likely evolves under selection from extreme warming events more than mean temperature, and cold tolerance in the tropics seems to be more selected for by mean annual temperature. Extreme heat spikes are predicted to become more common because of anthropogenic climate change. These changes may have most dangerous consequences for tropical species adapted to historically stable conditions. </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 climatic variability hypothesis (CVH) is a cornerstone of thermal ecology, predicting the evolution of wider organismal thermal tolerance ranges in more thermally variable environments. Thermal tolerance ranges depend on both upper and lower tolerance limits (critical thermal maxima: CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span>, and critical thermal minima: CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span>), which may show different responses to environmental gradients. To delineate the relative effects of mean and extreme temperatures on thermal tolerances, we conducted a within-latitude comparative test of CVH predictions for army ants (Dorylinae) at multiple scales: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats. Consistent with the CVH, thermally-buffered subterranean species had narrower thermal tolerance ranges. Both CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span> and CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span> decreased with elevation for subterranean species. In contrast, aboveground species (those exposed to insolation) showed a decrease in CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span> but no change in CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span> across elevations. Furthermore, greater seasonal temperature variation in dry forests correlated with increased CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span>, but not CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span> These patterns suggest CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span> and CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span> respond to different abiotic selective forces: habitat-specific exposure to extreme insolation corresponds to CT<span style="font-size:70%; position:relative; bottom:-0.3em;">max</span> differences, but not to CT<span style="font-size:70%; position:relative; bottom:-0.3em;">min</span> variation. We predict increasingly frequent heat spikes associated with climate change will have habitat-specific physiological consequences for ectothermic animals. Models predicting climate change impacts should account for species microhabitat uses and within-latitude differences in temperature seasonality. </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, 09 May 2018 05:00:00 GMT “Born to run? Quantifying the balance of prior bias and new information in prey escape decisions” http://amnat.org/an/newpapers/SepSutton.html The DOI will be https://dx.doi.org/10.1086/698692 Optimality modeling, risk assessment, and Bayesian inference of prior experience predict prey escape decisions Wildlife, and specifically deer, are a common sight at state parks. But why do some deer seem to run away at the first sight of a human, while others will happily eat from the palm of your hand? And how can you tell how the deer at any given park are likely to respond to humans? In this manuscript, Nick Sutton, PhD student at the University of Illinois at Urbana-Champaign (UIUC), and James O’Dwyer, Assistant Professor at UIUC, find that this specific question provides insight into a deeper debate relating to the balance of old and new information in animal decision-making. Sutton and O’Dwyer collected data on the escape behavior of deer under human approach, and combined this with a model evaluating the costs and benefits to deer of remaining around humans versus fleeing from them. The resulting predictions depend on a balance of previous experience of humans for a given deer, and new information gathered during an encounter. Using this approach, Sutton and O’Dwyer inferred the effects of past experiences on deer behavior at the population level, and evaluated multiple sources of information that deer are using when making the decision to flee, such as how fast humans are moving or how far away they are. By inferring the prior experiences of deer and comparing models based on different types of information, Sutton and O’Dwyer found that they can accurately predict the distance at which deer decide to flee, and that how close humans can get will vary between parks. This new modeling approach provides general methods for predicting the optimal moment to make a high-stakes decision, such as deer deciding when to flee from humans. The approach can also apply to other taxa, even humans, whenever decisions are based on a combination of prior experience, costs/benefits and new information. Abstract Animal behaviors can often be challenging to model and predict, though optimality theory has improved our ability to do so. While many qualitative predictions of behavior exist, accurate quantitative models, tested by empirical data, are often lacking. This is likely due to variation in biases across individuals and variation in the way new information is gathered and used. We propose a modeling framework based on a novel interpretation of Bayes’ theorem to integrate optimization of energetic constraints with both prior biases and specific sources of new information gathered by individuals. We present methods for inferring distributions of prior biases within populations rather than assuming known priors, as is common in Bayesian approaches to modelling behavior, and for evaluating the goodness of fit of overall model descriptions. We apply this framework to predict optimal escape during predator-prey encounters, based on prior biases and variation in what information prey use. Using this approach we collected and analyzed data characterizing white-tailed deer (Odocoileus virginianus) escape behavior in response to human approaches. We found that distance to predator alone was not sufficient to predict deer flight response, and show that the inclusion of additional information is necessary. Additionally, we compared differences in the inferred distributions of prior biases across different populations and discuss the possible role of human activity in influencing these distributions. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698692 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698692">Read the Article</a></i> </p> --> <p><b>Optimality modeling, risk assessment, and Bayesian inference of prior experience predict prey escape decisions </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>ildlife, and specifically deer, are a common sight at state parks. But why do some deer seem to run away at the first sight of a human, while others will happily eat from the palm of your hand? And how can you tell how the deer at any given park are likely to respond to humans? In this manuscript, Nick Sutton, PhD student at the University of Illinois at Urbana-Champaign (UIUC), and James O’Dwyer, Assistant Professor at UIUC, find that this specific question provides insight into a deeper debate relating to the balance of old and new information in animal decision-making. Sutton and O’Dwyer collected data on the escape behavior of deer under human approach, and combined this with a model evaluating the costs and benefits to deer of remaining around humans versus fleeing from them. The resulting predictions depend on a balance of previous experience of humans for a given deer, and new information gathered during an encounter.</p> <p>Using this approach, Sutton and O’Dwyer inferred the effects of past experiences on deer behavior at the population level, and evaluated multiple sources of information that deer are using when making the decision to flee, such as how fast humans are moving or how far away they are. By inferring the prior experiences of deer and comparing models based on different types of information, Sutton and O’Dwyer found that they can accurately predict the distance at which deer decide to flee, and that how close humans can get will vary between parks. This new modeling approach provides general methods for predicting the optimal moment to make a high-stakes decision, such as deer deciding when to flee from humans. The approach can also apply to other taxa, even humans, whenever decisions are based on a combination of prior experience, costs/benefits and new information. </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>nimal behaviors can often be challenging to model and predict, though optimality theory has improved our ability to do so. While many qualitative predictions of behavior exist, accurate quantitative models, tested by empirical data, are often lacking. This is likely due to variation in biases across individuals and variation in the way new information is gathered and used. We propose a modeling framework based on a novel interpretation of Bayes’ theorem to integrate optimization of energetic constraints with both prior biases and specific sources of new information gathered by individuals. We present methods for inferring distributions of prior biases within populations rather than assuming known priors, as is common in Bayesian approaches to modelling behavior, and for evaluating the goodness of fit of overall model descriptions. We apply this framework to predict optimal escape during predator-prey encounters, based on prior biases and variation in what information prey use. Using this approach we collected and analyzed data characterizing white-tailed deer (<i>Odocoileus virginianus</i>) escape behavior in response to human approaches. We found that distance to predator alone was not sufficient to predict deer flight response, and show that the inclusion of additional information is necessary. Additionally, we compared differences in the inferred distributions of prior biases across different populations and discuss the possible role of human activity in influencing these distributions. </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, 09 May 2018 05:00:00 GMT “Plant strategies along resource gradients” http://amnat.org/an/newpapers/SepKoffel-A.html The DOI will be https://dx.doi.org/10.1086/698600 New eco-evo model on plant tolerance vs. resistance against herbivores along a resource gradient Abstract Plants present a variety of defensive strategies against herbivores, broadly classified into tolerance and resistance. Since resource availability can also limit plant growth, we expect plant allocation to resource acquisition and defense to vary along resource gradients. Yet, the conditions under which one defensive strategy is favored over the other are unclear. Here, we use an eco-evolutionary model to investigate plant adaptive allocation to resource acquisition, tolerance and resistance along a resource gradient in a simple food web module inspired by plankton communities where plants compete for a single resource and are grazed upon by a shared herbivore. We show that undefended, acquisition-specialist strategies dominate under low resource supplies. Conversely, high resource supplies, which lead to high herbivore abundance because of trophic transfers, result in either the dominance of very resistant strategies or coexistence between a completely resistant strategy and a fast-growing, tolerant one. We also explore the consequences of this adaptive allocation on species biomasses. Finally, we compare our predictions to a more traditional, density-independent optimization model. We show that density-dependence mediated by resources and herbivores is the cause of the increase in plant resistance along the resource gradient, as the optimization model would instead have favored tolerance. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698600 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698600">Read the Article</a></i> </p> --> <p><b>New eco-evo model on plant tolerance vs. resistance against herbivores along a resource gradient </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;">P</span>lants present a variety of defensive strategies against herbivores, broadly classified into tolerance and resistance. Since resource availability can also limit plant growth, we expect plant allocation to resource acquisition and defense to vary along resource gradients. Yet, the conditions under which one defensive strategy is favored over the other are unclear. Here, we use an eco-evolutionary model to investigate plant adaptive allocation to resource acquisition, tolerance and resistance along a resource gradient in a simple food web module inspired by plankton communities where plants compete for a single resource and are grazed upon by a shared herbivore. We show that undefended, acquisition-specialist strategies dominate under low resource supplies. Conversely, high resource supplies, which lead to high herbivore abundance because of trophic transfers, result in either the dominance of very resistant strategies or coexistence between a completely resistant strategy and a fast-growing, tolerant one. We also explore the consequences of this adaptive allocation on species biomasses. Finally, we compare our predictions to a more traditional, density-independent optimization model. We show that density-dependence mediated by resources and herbivores is the cause of the increase in plant resistance along the resource gradient, as the optimization model would instead have favored tolerance. </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, 09 May 2018 05:00:00 GMT “Mating opportunity increases with synchrony of flowering among years more than synchrony within years in a non-masting perennial” http://amnat.org/an/newpapers/SepWaananen.html The DOI will be https://dx.doi.org/10.1086/698657 Timing of mating among years matters as much, or more, than timing within years, even in non-masting species Plants can’t actively search for mates, so timing of flowering is critical for their reproduction. For years, research has characterized patterns of reproduction among years in species that “mast,” or show dramatic variation in annual reproductive effort—think of forest floors littered with oak tree acorns in a mast year, sudden blooms of desert annuals after rain, or bamboos, which grow for decades until they invest all their resources in one fatal reproductive episode. For these species, flowering synchronously with their neighbors, i.e. flowering in the same year or years, is critical for finding a mate. Although reproduction in non-masting species may also vary from year to year, reproductive synchrony of these species is usually studied within seasons (i.e., the days individuals flower relative to their neighbors). In this study, the authors investigate the extent to which among- and within-year flowering synchrony influences individuals’ number of potential mates in a non-masting species. They used an 11-year dataset of flowering phenology of the long-lived perennial herb, Echinacea angustifolia. Surprisingly, they found that among-year synchrony contributed to variation in individuals’ long-term mating opportunities 39% more than within-year synchrony. This finding is important because it is demonstrates that among-year timing of reproduction may be an important determinant of mating opportunity not only in masting species, but also for many other species in which population reproduction varies among years. Abstract The timing and synchrony of mating activity in a population may vary both within and among years. With the exception of masting species, in which reproductive activity fluctuates dramatically among years, mating synchrony is typically studied within years. However, opportunities to mate also vary among years in non-masting iteroparous species. We demonstrate that studying only within-year flowering synchrony fails to accurately quantify variation in mating opportunity in an experimental population (n&nbsp;=&nbsp;286) of a non-masting species, Echinacea angustifolia. We quantified individuals’ synchrony of flowering within and among years and partitioned the contribution of each measure to mean daily mating potential, the number of potential mates per individual per day, averaged over every day it flowered during the 11-year study period. Individual within- and among-year synchrony displayed wide variation and were weakly correlated. In particular, among-year synchrony explained 39% more variation in mean daily mating potential than did within-year synchrony. Among-year synchrony could have underappreciated significance for mating dynamics in non-masting species. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698657 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698657">Read the Article</a></i> </p> --> <p><b>Timing of mating among years matters as much, or more, than timing within years, even in non-masting species </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>lants can’t actively search for mates, so timing of flowering is critical for their reproduction. For years, research has characterized patterns of reproduction among years in species that “mast,” or show dramatic variation in annual reproductive effort—think of forest floors littered with oak tree acorns in a mast year, sudden blooms of desert annuals after rain, or bamboos, which grow for decades until they invest all their resources in one fatal reproductive episode. For these species, flowering synchronously with their neighbors, i.e. flowering in the same year or years, is critical for finding a mate. Although reproduction in non-masting species may also vary from year to year, reproductive synchrony of these species is usually studied within seasons (i.e., the days individuals flower relative to their neighbors). In this study, the authors investigate the extent to which among- <i>and</i> within-year flowering synchrony influences individuals’ number of potential mates in a non-masting species. They used an 11-year dataset of flowering phenology of the long-lived perennial herb, <i>Echinacea angustifolia</i>. Surprisingly, they found that among-year synchrony contributed to variation in individuals’ long-term mating opportunities 39% more than within-year synchrony. This finding is important because it is demonstrates that among-year timing of reproduction may be an important determinant of mating opportunity not only in masting species, but also for many other species in which population reproduction varies among years. </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 timing and synchrony of mating activity in a population may vary both within and among years. With the exception of masting species, in which reproductive activity fluctuates dramatically among years, mating synchrony is typically studied within years. However, opportunities to mate also vary among years in non-masting iteroparous species. We demonstrate that studying only within-year flowering synchrony fails to accurately quantify variation in mating opportunity in an experimental population (n&nbsp;=&nbsp;286) of a non-masting species, <i>Echinacea angustifolia</i>. We quantified individuals’ synchrony of flowering within and among years and partitioned the contribution of each measure to mean daily mating potential, the number of potential mates per individual per day, averaged over every day it flowered during the 11-year study period. Individual within- and among-year synchrony displayed wide variation and were weakly correlated. In particular, among-year synchrony explained 39% more variation in mean daily mating potential than did within-year synchrony. Among-year synchrony could have underappreciated significance for mating dynamics in non-masting species. </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, 09 May 2018 05:00:00 GMT “Ontogeny and consistent individual differences mediate trophic interactions” http://amnat.org/an/newpapers/SepStart.html The DOI will be https://dx.doi.org/10.1086/698693 In the world of dragonflies, age and individual behavioral differences combine to determine who eats who Traits shape where species can occur, and consequently the assembly of ecological communities. However, species’ traits are not invariant—individuals of the same species are often markedly different, with probable consequences for entire communities. Individuals can differ in appearance or behavior because of (1) consistent individual differences or (2) because individual traits change across the lifetime of the organism (across ontogeny). Do consistent individual differences and ontogenetic shifts have similar impacts on community assembly? What is the joint effect of both types of individual variation? Start addresses these questions by developing a conceptual understanding of consistent individual differences and ontogenetic trait shifts. He goes on to demonstrate the utility of considering multiple sources of intraspecific variation using dragonfly larvae in an aquatic mesocosm experiment. Start argues that the effect of a consistent individual trait difference will depend on the functional role of that individual in the community, itself a function of ontogeny. Using an aquatic mesocosm experiment at the Koffler Scientific Reserve (University of Toronto), he shows that young dragonfly larvae are often prey to larger dragonflies, demonstrating an ontogenetic shift in functional role from prey to predator. Individual dragonfly larvae also differ in activity rate, but the effect of activity rate depends on ontogenetic stage; young and active dragonfly larvae are more likely to be consumed by a predator, but older and active dragonfly larvae are themselves the most voracious predators. Start ultimately shows that the effects of ontogeny and consistent individual differences are interactive, jointly shaping species interactions and the assembly of ecological communities. We are increasingly recognizing the importance of considering processes occurring across biological scales (e.g. individuals to communities). Start provides a road map for considering when ontogeny and consistent individual differences will shape ecological communities; given the large trait differences observed in many populations, and the ubiquity of changes across the lifecycle, the framework presented here is likely to have general utility for virtually all ecological systems. Abstract Ecologists use species traits to predict individual responses to environmental change, and ultimately to understand the composition of biological communities. However, this ignores known and substantial intraspecific variation that can have important consequences for species interactions and community composition. This within-species variation results from two distinct sources: ontogeny and consistent individual differences. Ontogeny and consistent differences interact to produce phenotypes, but the community-level consequences of this interaction have not been studied. Using larval dragonfly communities I investigate patterns of intraguild predation by manipulating (1) consistent individual differences in activity rate, and (2) the ontogeny of the focal and interacting species. I show that activity rate is a consistent individual trait, but that the effect of activity rate on intraguild predation depends on the functional role of an organism in the community (predator or prey). An organism’s functional role itself varies across ontogeny of both the focal and interacting individuals. I suggest that ontogeny and consistent individual differences interact to produce intraspecific variation, with consequences for species interactions, communities, and eco-evolutionary dynamics. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698693 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698693">Read the Article</a></i> </p> --> <p><b>In the world of dragonflies, age and individual behavioral differences combine to determine who eats who </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>raits shape where species can occur, and consequently the assembly of ecological communities. However, species’ traits are not invariant—individuals of the same species are often markedly different, with probable consequences for entire communities. Individuals can differ in appearance or behavior because of (1) consistent individual differences or (2) because individual traits change across the lifetime of the organism (across ontogeny). Do consistent individual differences and ontogenetic shifts have similar impacts on community assembly? What is the joint effect of both types of individual variation? Start addresses these questions by developing a conceptual understanding of consistent individual differences and ontogenetic trait shifts. He goes on to demonstrate the utility of considering multiple sources of intraspecific variation using dragonfly larvae in an aquatic mesocosm experiment. </p><p>Start argues that the effect of a consistent individual trait difference will depend on the functional role of that individual in the community, itself a function of ontogeny. Using an aquatic mesocosm experiment at the Koffler Scientific Reserve (University of Toronto), he shows that young dragonfly larvae are often prey to larger dragonflies, demonstrating an ontogenetic shift in functional role from prey to predator. Individual dragonfly larvae also differ in activity rate, but the effect of activity rate depends on ontogenetic stage; young and active dragonfly larvae are more likely to be consumed by a predator, but older and active dragonfly larvae are themselves the most voracious predators. Start ultimately shows that the effects of ontogeny and consistent individual differences are interactive, jointly shaping species interactions and the assembly of ecological communities. </p><p>We are increasingly recognizing the importance of considering processes occurring across biological scales (e.g. individuals to communities). Start provides a road map for considering when ontogeny and consistent individual differences will shape ecological communities; given the large trait differences observed in many populations, and the ubiquity of changes across the lifecycle, the framework presented here is likely to have general utility for virtually all ecological systems. </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;">E</span>cologists use species traits to predict individual responses to environmental change, and ultimately to understand the composition of biological communities. However, this ignores known and substantial intraspecific variation that can have important consequences for species interactions and community composition. This within-species variation results from two distinct sources: ontogeny and consistent individual differences. Ontogeny and consistent differences interact to produce phenotypes, but the community-level consequences of this interaction have not been studied. Using larval dragonfly communities I investigate patterns of intraguild predation by manipulating (1) consistent individual differences in activity rate, and (2) the ontogeny of the focal and interacting species. I show that activity rate is a consistent individual trait, but that the effect of activity rate on intraguild predation depends on the functional role of an organism in the community (predator or prey). An organism’s functional role itself varies across ontogeny of both the focal and interacting individuals. I suggest that ontogeny and consistent individual differences interact to produce intraspecific variation, with consequences for species interactions, communities, and eco-evolutionary 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> Wed, 09 May 2018 05:00:00 GMT “Sexual conflict: Mechanisms and emerging themes in resistance biology” http://amnat.org/an/newpapers/VP-Chapman.html Read the Article Battles between the interests of males and females over reproductive decisions, such as how often to mate and how much to invest now versus later, are widespread. Much progress has been made over the past few decades in understanding why and how these battles occur. Broadly speaking, in situations where reproducing partners have little shared interest in each other’s reproductive futures, they can sometimes benefit by exploiting, rather than fully cooperating with, their mates. Much work into the details of how these sexual conflicts are manifested has been done in insects, due to their ease of study and manipulation. In particular, studies on Drosophila fruitflies has revealed a fascinating covert battleground between males and females mediated by the actions of seminal fluid proteins passed from males to females during mating along with sperm. These proteins affect the behavior and physiology of the female in dramatic ways by altering her egg laying, sexual receptivity, feeding, and immune genes. Males can sometimes gain by using these proteins to make females invest more in current versus future reproductive episodes, even though this can be harmful to females in the longer term, e.g. by shortening their lifespan. In this situation, females should evolve resistance to these proteins to avoid this harm. A stand-out feature of seminal fluid proteins involved in mediating sexual conflict is their complexity. In this article, the idea is explored that this complexity arises in part as a strategy to allow males to effectively manipulate the reproductive system of females in a way that makes it hard for females to resist. This idea comes from examining parallels with the strategies employed by humans to slow the evolution of resistance to pesticides and antimicrobial drugs. Strategies in which males employ multiple manipulative pathways across time and space are predicted to be the most effective at slowing female counter responses. Thinking about the problem in this way may provide a new way in which to study the manipulative strategies of males towards females and specifically to explain why some male strategies are ‘resistance proof’ and hence persist, while others aren’t and don’t. Abstract Sexual conflict is acknowledged as pervasive, with the potential to generate and maintain genetic variation. Mechanistic studies of conflict have been important in providing direct evidence for the existence of sexual conflict. They have also led to the growing realization that there is a striking phenotypic diversity of adaptations whose evolution can be shaped by sexually antagonistic selection. The mechanisms involved range from the use of genital spines, claspers, songs, smells to ejaculate molecules. In one well-studied example, sexual conflict can occur over the sexually antagonistic effects of seminal fluid proteins in Drosophila melanogaster. However, an important puzzle remains, namely why seminal fluid proteins are so numerous and complex, hence whether all or some are involved in mediating sexual conflict. I hypothesize that this rich diversity, and the complexity of traits subject to sexually antagonistic selection in general, may arise, at least in part, due to the deployment of sexually antagonistic adaptations in males in a way that lessens the probability of broad scale, strong resistance evolution in females. In elaborating this hypothesis I explore how research into the evolution of resistance to insecticides, antimicrobials and vaccines might be used to provide insights into the evolution of female resistance to the effects of sexually antagonistic manipulative traits of males. In this manner, the manipulative traits of males can be resistance-proofed. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698169"><i>Read the Article</i></a></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698169">Read the Article</a></i></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>attles between the interests of males and females over reproductive decisions, such as how often to mate and how much to invest now versus later, are widespread. Much progress has been made over the past few decades in understanding why and how these battles occur. Broadly speaking, in situations where reproducing partners have little shared interest in each other&rsquo;s reproductive futures, they can sometimes benefit by exploiting, rather than fully cooperating with, their mates. Much work into the details of how these sexual conflicts are manifested has been done in insects, due to their ease of study and manipulation. In particular, studies on <i>Drosophila</i> fruitflies has revealed a fascinating covert battleground between males and females mediated by the actions of seminal fluid proteins passed from males to females during mating along with sperm. These proteins affect the behavior and physiology of the female in dramatic ways by altering her egg laying, sexual receptivity, feeding, and immune genes. Males can sometimes gain by using these proteins to make females invest more in current versus future reproductive episodes, even though this can be harmful to females in the longer term, e.g. by shortening their lifespan. In this situation, females should evolve resistance to these proteins to avoid this harm. A stand-out feature of seminal fluid proteins involved in mediating sexual conflict is their complexity. In this article, the idea is explored that this complexity arises in part as a strategy to allow males to effectively manipulate the reproductive system of females in a way that makes it hard for females to resist. This idea comes from examining parallels with the strategies employed by humans to slow the evolution of resistance to pesticides and antimicrobial drugs. Strategies in which males employ multiple manipulative pathways across time and space are predicted to be the most effective at slowing female counter responses. Thinking about the problem in this way may provide a new way in which to study the manipulative strategies of males towards females and specifically to explain why some male strategies are &lsquo;resistance proof&rsquo; and hence persist, while others aren&rsquo;t and don&rsquo;t.</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;">S</span>exual conflict is acknowledged as pervasive, with the potential to generate and maintain genetic variation. Mechanistic studies of conflict have been important in providing direct evidence for the existence of sexual conflict. They have also led to the growing realization that there is a striking phenotypic diversity of adaptations whose evolution can be shaped by sexually antagonistic selection. The mechanisms involved range from the use of genital spines, claspers, songs, smells to ejaculate molecules. In one well-studied example, sexual conflict can occur over the sexually antagonistic effects of seminal fluid proteins in <i>Drosophila melanogaster</i>. However, an important puzzle remains, namely why seminal fluid proteins are so numerous and complex, hence whether all or some are involved in mediating sexual conflict. I hypothesize that this rich diversity, and the complexity of traits subject to sexually antagonistic selection in general, may arise, at least in part, due to the deployment of sexually antagonistic adaptations in males in a way that lessens the probability of broad scale, strong resistance evolution in females. In elaborating this hypothesis I explore how research into the evolution of resistance to insecticides, antimicrobials and vaccines might be used to provide insights into the evolution of female resistance to the effects of sexually antagonistic manipulative traits of males. In this manner, the manipulative traits of males can be resistance-proofed.</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, 26 Apr 2018 05:00:00 GMT “The role of phenotypic plasticity in moderating evolutionary conflict” http://amnat.org/an/newpapers/VP-Day-A.html Read the Article Abstract Evolutionary conflicts arise when the fitness interests of interacting individuals differ. Well-known examples include sexual conflict between males and females and antagonistic coevolution between hosts and parasites. A common feature of such conflicts is that compensating evolutionary change in each of the parties can lead to little overt change in the interaction itself. As a result, evolutionary conflict is expected to persist even if the evolutionary dynamic between the parties reaches an equilibrium. In these cases it is of interest to know whether certain kinds of interactions are expected to lead to greater or lesser evolutionary conflict at such evolutionary stalemates. Here we present a theoretical analysis showing that when one of the interacting parties can respond to the other through adaptive phenotypic plasticity, evolutionary conflict is reduced. Paradoxically, however, it is the party that does not express adaptive plasticity that experiences less conflict. Conflict for the party displaying adaptive plasticity can increase or decrease depending on the situation. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698170"><i>Read the Article</i></a></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698170">Read the Article</a></i></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;">E</span>volutionary conflicts arise when the fitness interests of interacting individuals differ. Well-known examples include sexual conflict between males and females and antagonistic coevolution between hosts and parasites. A common feature of such conflicts is that compensating evolutionary change in each of the parties can lead to little overt change in the interaction itself. As a result, evolutionary conflict is expected to persist even if the evolutionary dynamic between the parties reaches an equilibrium. In these cases it is of interest to know whether certain kinds of interactions are expected to lead to greater or lesser evolutionary conflict at such evolutionary stalemates. Here we present a theoretical analysis showing that when one of the interacting parties can respond to the other through adaptive phenotypic plasticity, evolutionary conflict is reduced. Paradoxically, however, it is the party that does not express adaptive plasticity that experiences less conflict. Conflict for the party displaying adaptive plasticity can increase or decrease depending on the situation. </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, 26 Apr 2018 05:00:00 GMT “Socio-reproductive conflicts and the father’s curse dilemma” http://amnat.org/an/newpapers/VP-Mokkonen.html Read the Article Choice of mate has important implications for the survival and future reproductive success of offspring Successful reproduction involves finding a suitable mate, investing in offspring during its development, and then caring for the offspring after it is born. Females typically invest more in offspring through pregnancy and postnatal care, whereas males typically impact offspring indirectly through genetic effects. Such asymmetry between the sexes during reproduction results in sexual conflicts of interest over traits associated with mating and parental efforts. Focusing on mammals, and specifically on the well-studied bank vole (Myodes glareolus), Mokkonen and coauthors draw on studies from evolutionary ecology, endocrinology, and genetics to synthesize a new concept known as the father’s curse dilemma, which describes an evolutionary trade-off between quality of parental care and offspring quality. The authors have gathered evidence that trade-offs between mating and parenting can be mediated by the same genes, with different fitness effects in females compared to males. At the heart of the father’s curse dilemma is the finding that those genes that make females good parents are likely to render offspring, particularly males, less competitive later in life as adults. Thus, fathers are faced with a dilemma: Is it better to find a mate that will ensure better survival of offspring during parental care or a mate that will confer genes that make the offspring more competitive later in life? Abstract Evolutionary conflicts between males and females can manifest over sexually antagonistic interactions at loci, or over sexually antagonistic interests within a locus. The latter form of conflict, intra-locus sexual conflict, arises from sexually antagonistic selection and constrains the fitness of individuals through a phenotypic compromise. These conflicts, and socio-reproductive interactions in general, are commonly mediated by hormones, and thus, predictive insights can be gained from studying their mediating effects. Here, we integrate several lines of evidence to describe a novel, hormonally-mediated reproductive dilemma that we call the father’s curse, which results from an intra-locus conflict between mating and parental efforts. Essentially, a genetic locus exerts pleiotropic and antagonistic effects on the mating effort of one individual, and parental effort of a related individual who is the primary provider of parental care. We outline the criteria for operation of the father’s curse dilemma, provide evidence of the phenomenon, and discuss the predictions and outcomes arising from its dynamics. By integrating the effects of hormones into socio-reproductive conflicts and socio-reproductive effort, clearer links between genotypes, phenotypes and fitness can be established. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698216"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698216">Read the Article</a></i> </p> --> <p><b>Choice of mate has important implications for the survival and future reproductive success of offspring </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;">S</span>uccessful reproduction involves finding a suitable mate, investing in offspring during its development, and then caring for the offspring after it is born. Females typically invest more in offspring through pregnancy and postnatal care, whereas males typically impact offspring indirectly through genetic effects. Such asymmetry between the sexes during reproduction results in sexual conflicts of interest over traits associated with mating and parental efforts.</p> <p>Focusing on mammals, and specifically on the well-studied bank vole (<i>Myodes glareolus</i>), Mokkonen and coauthors draw on studies from evolutionary ecology, endocrinology, and genetics to synthesize a new concept known as the father&rsquo;s curse dilemma, which describes an evolutionary trade-off between quality of parental care and offspring quality. The authors have gathered evidence that trade-offs between mating and parenting can be mediated by the same genes, with different fitness effects in females compared to males. At the heart of the father&rsquo;s curse dilemma is the finding that those genes that make females good parents are likely to render offspring, particularly males, less competitive later in life as adults. Thus, fathers are faced with a dilemma: Is it better to find a mate that will ensure better survival of offspring during parental care or a mate that will confer genes that make the offspring more competitive later in life?</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;">E</span>volutionary conflicts between males and females can manifest over sexually antagonistic interactions at loci, or over sexually antagonistic interests within a locus. The latter form of conflict, intra-locus sexual conflict, arises from sexually antagonistic selection and constrains the fitness of individuals through a phenotypic compromise. These conflicts, and socio-reproductive interactions in general, are commonly mediated by hormones, and thus, predictive insights can be gained from studying their mediating effects. Here, we integrate several lines of evidence to describe a novel, hormonally-mediated reproductive dilemma that we call the father&rsquo;s curse, which results from an intra-locus conflict between mating and parental efforts. Essentially, a genetic locus exerts pleiotropic and antagonistic effects on the mating effort of one individual, and parental effort of a related individual who is the primary provider of parental care. We outline the criteria for operation of the father&rsquo;s curse dilemma, provide evidence of the phenomenon, and discuss the predictions and outcomes arising from its dynamics. By integrating the effects of hormones into socio-reproductive conflicts and socio-reproductive effort, clearer links between genotypes, phenotypes and fitness can be established.</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, 26 Apr 2018 05:00:00 GMT “The evolutionary consequences of selection at the haploid gametic stage” http://amnat.org/an/newpapers/VP-Immler-A.html Read the Article Abstract As an immediate consequence of sexual reproduction, biphasic life cycles with alternating diploid and haploid phases are a common characteristic of sexually reproducing eukaryotes. Much of our focus in evolutionary biology has been directed towards dynamics in diploid or haploid populations, but we rarely consider selection occurring during both phases when studying evolutionary processes. One of the reasons for this apparent omission is the fact that many flowering plants and metazoans are predominantly diploid with a very short haploid gametic phase. While this gametic phase may be short, it can play a crucial role in fundamental processes including the rate of adaptation, the load of mutation, and the evolution of features such as recombination. In addition, if selection acts in different or even opposite directions between the two phases, a genetic conflict will occur, impacting the maintenance of genetic variation. Here we provide an overview of theoretical and empirical studies investigating the importance of selection at the haploid gametic phase in predominantly diploid organisms and discuss future directions to improve our understanding of the underlying dynamics and the general implications of haploid selection. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698483"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698483">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;">A</span>s an immediate consequence of sexual reproduction, biphasic life cycles with alternating diploid and haploid phases are a common characteristic of sexually reproducing eukaryotes. Much of our focus in evolutionary biology has been directed towards dynamics in diploid or haploid populations, but we rarely consider selection occurring during both phases when studying evolutionary processes. One of the reasons for this apparent omission is the fact that many flowering plants and metazoans are predominantly diploid with a very short haploid gametic phase. While this gametic phase may be short, it can play a crucial role in fundamental processes including the rate of adaptation, the load of mutation, and the evolution of features such as recombination. In addition, if selection acts in different or even opposite directions between the two phases, a genetic conflict will occur, impacting the maintenance of genetic variation. Here we provide an overview of theoretical and empirical studies investigating the importance of selection at the haploid gametic phase in predominantly diploid organisms and discuss future directions to improve our understanding of the underlying dynamics and the general implications of haploid selection. </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, 26 Apr 2018 05:00:00 GMT “The genomics of sexual conflict” http://amnat.org/an/newpapers/VP-Rowe-A.html Read the Article Abstract Sexual dimorphism is a substantial contributor to the diversity observed in nature, extending from elaborate traits to the expression level of individual genes. Sexual conflict and sexually antagonistic coevolution are thought to be central forces driving the dimorphism of the sexes and its diversity. We have substantial data to support this at the phenotypic level, but much less at the genetic level, where distinguishing a role conflict from other forms of sex-biased selection and from other processes is challenging. Here we discuss the powerful effects sexual conflict may have on genome evolution, and critically evaluate the supporting evidence. Although there is much potential for sexual conflict to affect genome evolution, we have relatively little compelling evidence of a genomic signature of sexual conflict. A central obstacle is the mismatch between taxa in which we understand sexually antagonistic selection and those in which we understand genetics. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698198"><i>Read the Article</i></a></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698198">Read the Article</a></i></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;">S</span>exual dimorphism is a substantial contributor to the diversity observed in nature, extending from elaborate traits to the expression level of individual genes. Sexual conflict and sexually antagonistic coevolution are thought to be central forces driving the dimorphism of the sexes and its diversity. We have substantial data to support this at the phenotypic level, but much less at the genetic level, where distinguishing a role conflict from other forms of sex-biased selection and from other processes is challenging. Here we discuss the powerful effects sexual conflict may have on genome evolution, and critically evaluate the supporting evidence. Although there is much potential for sexual conflict to affect genome evolution, we have relatively little compelling evidence of a genomic signature of sexual conflict. A central obstacle is the mismatch between taxa in which we understand sexually antagonistic selection and those in which we understand genetics. </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, 26 Apr 2018 05:00:00 GMT “Evolutionary conflict between mobile DNA and their host genome” http://amnat.org/an/newpapers/VP-Song.html Read the Article It is now known that most plant and animal genomes are full of DNA that once could, and in some cases still can, move around. Mobile DNA (also referred to as “selfish” DNA) can either jump from position to position in the genome, or replicate itself and accrue lots of copies over time. In many cases, it will eventually lose ability to move or be silenced by the genome it has invaded. But in some cases, it can be co-opted by the genome it has invaded, and begin to provide important functions for the host instead of simply facilitating its own movement. In this paper, the authors explore the range of possible resolutions to the evolutionary conflict between DNA that can move and replicate and the host genome in which it is found. In order to understand the range of outcomes better, they illustrate the various stages at which conflict can occur and be resolved. Moreover, they highlight the most well-developed bodies of ecological and evolutionary theory from which one can borrow to try and predict the outcomes of conflicts between selfish DNA and their hosts. Abstract The proportion of eukaryotic genomes comprised of active or formerly active mobile elements (MEs) is known to vary widely across lineages, but the explanations for why remain largely unknown. Given that ME activity, like other forms of mutation, is thought to be (on average) slightly deleterious in terms of phenotypic effects, understanding the widespread proliferation of MEs in host genomes requires an evolutionary framework. To better develop such a framework, we review the spectrum of resolutions to the genetic conflict between MEs and their hosts: inactivation of MEs due to mutation accumulation, negative selection (or lack thereof) against hosts with high ME loads, silencing of MEs (by hosts or MEs), ME domestication by their hosts, and the horizontal transfer of MEs to new hosts. We also highlight ecological and evolutionary theory from which ME researchers might borrow in order to explain large-scale patterns of ME dynamics across systems. We hope a synthesis of the surprisingly significant role of MEs in the genome, as well as the spectrum of resolutions, applicable theory, and recent discoveries, will have two outcomes for future researchers: better parsing of known variation in ME proliferation patterns across genomes and the development of testable models and predictions regarding the evolutionary trajectory of MEs based on a combination of theory, the comparative method, experimental evolution, and empirical observations. More forthcoming papers &raquo; <p><strong><a href="https://dx.doi.org/10.1086/698482"><i>Read the Article</i></a></strong></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698482">Read the Article</a></i> </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;">I</span>t is now known that most plant and animal genomes are full of DNA that once could, and in some cases still can, move around. Mobile DNA (also referred to as &ldquo;selfish&rdquo; DNA) can either jump from position to position in the genome, or replicate itself and accrue lots of copies over time. In many cases, it will eventually lose ability to move or be silenced by the genome it has invaded. But in some cases, it can be co-opted by the genome it has invaded, and begin to provide important functions for the host instead of simply facilitating its own movement. In this paper, the authors explore the range of possible resolutions to the evolutionary conflict between DNA that can move and replicate and the host genome in which it is found. In order to understand the range of outcomes better, they illustrate the various stages at which conflict can occur and be resolved. Moreover, they highlight the most well-developed bodies of ecological and evolutionary theory from which one can borrow to try and predict the outcomes of conflicts between selfish DNA and their hosts.</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>he proportion of eukaryotic genomes comprised of active or formerly active mobile elements (MEs) is known to vary widely across lineages, but the explanations for why remain largely unknown. Given that ME activity, like other forms of mutation, is thought to be (on average) slightly deleterious in terms of phenotypic effects, understanding the widespread proliferation of MEs in host genomes requires an evolutionary framework. To better develop such a framework, we review the spectrum of resolutions to the genetic conflict between MEs and their hosts: inactivation of MEs due to mutation accumulation, negative selection (or lack thereof) against hosts with high ME loads, silencing of MEs (by hosts or MEs), ME domestication by their hosts, and the horizontal transfer of MEs to new hosts. We also highlight ecological and evolutionary theory from which ME researchers might borrow in order to explain large-scale patterns of ME dynamics across systems. We hope a synthesis of the surprisingly significant role of MEs in the genome, as well as the spectrum of resolutions, applicable theory, and recent discoveries, will have two outcomes for future researchers: better parsing of known variation in ME proliferation patterns across genomes and the development of testable models and predictions regarding the evolutionary trajectory of MEs based on a combination of theory, the comparative method, experimental evolution, and empirical observations.</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, 26 Apr 2018 05:00:00 GMT “Assessing feeding preference of a consumer guild: partitioning variation among versus within species” http://amnat.org/an/newpapers/SepRhoades-A.html The DOI will be https://dx.doi.org/10.1086/698325 Abstract Interspecific variation in resource use is critical to understanding species diversity, coexistence, and ecosystem functioning. A growing body of research describes analogous intraspecific variation and its potential importance for population dynamics and community outcomes. However, the magnitude of intraspecific variation relative to interspecific variation in key dimensions of consumer-resource interactions remains unknown, and is critical for understanding the importance of this variation for population and community processes. In this study, we examine feeding preference through repeated laboratory choice feeding assays of 444 wild-caught individuals of eight invertebrate grazer species on rocky reefs in northern California, USA. Between-species variation accounted for 25-33% of the total variation in preference for the preferred resource, while between-individual variation accounted for 4-5% of total variation. For two of the eight species, between-individual variation was significantly different from zero and contributed on-average 14% and 17% of the total diet variation, even after accounting for differences due to size and sex. Therefore, even with clearly distinguishable between-species differences in mean preference, diet variation between and within individuals can contribute to the dietary niche width of species and guilds, which may be overlooked by focusing solely on species’ mean resource use patterns. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698325 </i></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698325">Read the Article</a></i></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;">I</span>nterspecific variation in resource use is critical to understanding species diversity, coexistence, and ecosystem functioning. A growing body of research describes analogous intraspecific variation and its potential importance for population dynamics and community outcomes. However, the magnitude of intraspecific variation relative to interspecific variation in key dimensions of consumer-resource interactions remains unknown, and is critical for understanding the importance of this variation for population and community processes. In this study, we examine feeding preference through repeated laboratory choice feeding assays of 444 wild-caught individuals of eight invertebrate grazer species on rocky reefs in northern California, USA. Between-species variation accounted for 25-33% of the total variation in preference for the preferred resource, while between-individual variation accounted for 4-5% of total variation. For two of the eight species, between-individual variation was significantly different from zero and contributed on-average 14% and 17% of the total diet variation, even after accounting for differences due to size and sex. Therefore, even with clearly distinguishable between-species differences in mean preference, diet variation between and within individuals can contribute to the dietary niche width of species and guilds, which may be overlooked by focusing solely on species’ mean resource use patterns. </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, 19 Apr 2018 05:00:00 GMT “Multicellularity drives the evolution of sexual traits” http://amnat.org/an/newpapers/SepHanschen.html The DOI will be https://dx.doi.org/10.1086/698301 Multicellularity causes the evolution of sexual traits including anisogamy Sex didn’t always involve males and females. In fact, sex existed before males and females, and many species are still doing it without them. Males and females are defined by the different sizes of gametes they produce, and not all species produce two different sizes of gametes. Why sperm-producing males and egg-producing females evolved from ancestors without differentiated gametes is a major problem in evolutionary biology. Work led by Erik Hanschen that involved scientists at the University of Arizona, Georgia Tech, and the University of Tokyo suggests that the evolution of large, multicellular bodies drove the evolution of male and female sexes. Using the volvocine green algae to test mathematical theory dating back to the 1970s, they showed a positive relationship between body size and derived sexual characters, starting with different sized gametes (sperm and eggs). Larger species are more likely to have internal fertilization, as in mammals, while smaller species have external fertilization, as in most fishes. Body size is also related to the evolution of secondary sexual dimorphism, differences between males and females of the same species beyond their gametes. As in many birds, mammals, and other animals, male and female individuals of some large volvocine algae differ in their physical characteristics. The convergence of these patterns between the volvocine algae and other taxa suggests that the same principles apply to the evolution of the sexes in other groups, including plants and animals. The evolution of males and females, and subsequently of secondary sexual dimorphism, may be an inevitable consequence of the evolution of large, multicellular bodies. Abstract From the male peacock’s tail plumage to the floral displays of flowering plants, traits related to sexual reproduction are often complex and exaggerated. Why has sexual reproduction become so complicated? Why have such exaggerated sexual traits evolved? Early work posited a connection between multicellularity and sexual traits such as anisogamy (i.e., the evolution of small sperm and large eggs). Anisogamy then drives the evolution of other forms of sexual dimorphism. Yet, the relationship between multicellularity and the evolution of sexual traits has not been empirically tested. Given their extensive variation in both multicellular complexity and sexual systems, the volvocine green algae offer a tractable system for understanding the interrelationship of multicellular complexity and sex. Here we show that species with greater multicellular complexity have a significantly larger number of derived sexual traits, including anisogamy, internal fertilization, and secondary sexual dimorphism. Our results demonstrate that anisogamy repeatedly evolved from isogamous multicellular ancestors and that anisogamous species are larger and produce larger zygotes than isogamous species. In the volvocine algae, the evolution of multicellularity likely drives the evolution of anisogamy, and anisogamy subsequently drives secondary sexual dimorphism. Multicellularity may set the stage for the overall diversity of sexual complexity throughout the Tree of Life. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698301 </i></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698301">Read&nbsp;the&nbsp;Article</a> </b></i></p> --> <p><b>Multicellularity causes the evolution of sexual traits including anisogamy </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;">S</span>ex didn&rsquo;t always involve males and females. In fact, sex existed before males and females, and many species are still doing it without them. Males and females are defined by the different sizes of gametes they produce, and not all species produce two different sizes of gametes. Why sperm-producing males and egg-producing females evolved from ancestors without differentiated gametes is a major problem in evolutionary biology. Work led by Erik Hanschen that involved scientists at the University of Arizona, Georgia Tech, and the University of Tokyo suggests that the evolution of large, multicellular bodies drove the evolution of male and female sexes. Using the volvocine green algae to test mathematical theory dating back to the 1970s, they showed a positive relationship between body size and derived sexual characters, starting with different sized gametes (sperm and eggs). Larger species are more likely to have internal fertilization, as in mammals, while smaller species have external fertilization, as in most fishes. Body size is also related to the evolution of secondary sexual dimorphism, differences between males and females of the same species beyond their gametes. As in many birds, mammals, and other animals, male and female individuals of some large volvocine algae differ in their physical characteristics. The convergence of these patterns between the volvocine algae and other taxa suggests that the same principles apply to the evolution of the sexes in other groups, including plants and animals. The evolution of males and females, and subsequently of secondary sexual dimorphism, may be an inevitable consequence of the evolution of large, multicellular bodies.</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;">F</span>rom the male peacock&rsquo;s tail plumage to the floral displays of flowering plants, traits related to sexual reproduction are often complex and exaggerated. Why has sexual reproduction become so complicated? Why have such exaggerated sexual traits evolved? Early work posited a connection between multicellularity and sexual traits such as anisogamy (i.e., the evolution of small sperm and large eggs). Anisogamy then drives the evolution of other forms of sexual dimorphism. Yet, the relationship between multicellularity and the evolution of sexual traits has not been empirically tested. Given their extensive variation in both multicellular complexity and sexual systems, the volvocine green algae offer a tractable system for understanding the interrelationship of multicellular complexity and sex. Here we show that species with greater multicellular complexity have a significantly larger number of derived sexual traits, including anisogamy, internal fertilization, and secondary sexual dimorphism. Our results demonstrate that anisogamy repeatedly evolved from isogamous multicellular ancestors and that anisogamous species are larger and produce larger zygotes than isogamous species. In the volvocine algae, the evolution of multicellularity likely drives the evolution of anisogamy, and anisogamy subsequently drives secondary sexual dimorphism. Multicellularity may set the stage for the overall diversity of sexual complexity throughout the Tree of Life.</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, 19 Apr 2018 05:00:00 GMT “A probable case of incipient speciation in Schizocosa wolf spiders driven by allochrony, habitat use, and female mate choice” http://amnat.org/an/newpapers/SepGilman.html The DOI will be https://dx.doi.org/10.1086/698302 Behavioral work reveals new incipient species pair in Schizocosa wolf spiders Understanding the mechanisms that produce reproductive isolation and promote speciation has been a major goal of biologists since Darwin. In this paper, researchers report the discovery of a previously unrecognized ongoing speciation process in a well-studied population of wolf spiders in Oxford, Mississippi. The team showed that preferences for different habitat types, differences in maturation time, and female mate choice all contribute to reproductive isolation between sexually ornamented and unornamented spider morphotypes. This work suggests that speciation may not be driven by single mechanisms, but rather by suites of mechanisms operating together. The discovery of a new ongoing speciation process in wolf spiders adds to the short list of systems that scientists can use to study how speciation happens, and suggests that there may be additional species to discover even in well-studied systems. Abstract There is growing evidence that speciation can occur between populations that are not geographically isolated. The emergence of assortative mating is believed to be critical to this process, but how assortative mating arises in diverging populations is poorly understood. The wolf spider genus Schizocosa has become a model system for studying mechanisms of assortative mating. We conducted a series of experiments to identify the factors that control mate pair formation in a Schizocosa population that includes both ornamented and non-ornamented males. We show that the population also includes two previously unrecognized female phenotypes. One female phenotype mates mostly or exclusively with ornamented males, and the other mates mostly or exclusively with unornamented males. Assortative mating within these groups is maintained by differences in maturation time, microhabitat use, and female mate preference. We conclude that the population is not a single species as previously believed, but rather an incipient species pair with multiple overlapping mechanisms of reproductive isolation. The identification of a new incipient species pair in the well-studied and rapidly speciating Schizocosa clade presents new opportunities for the study of speciation without geographic isolation. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698302 </i></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698302">Read the Article</a></i></b> </p> --> <p><b>Behavioral work reveals new incipient species pair in <i>Schizocosa</i> wolf spiders </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;">U</span>nderstanding the mechanisms that produce reproductive isolation and promote speciation has been a major goal of biologists since Darwin. In this paper, researchers report the discovery of a previously unrecognized ongoing speciation process in a well-studied population of wolf spiders in Oxford, Mississippi. The team showed that preferences for different habitat types, differences in maturation time, and female mate choice all contribute to reproductive isolation between sexually ornamented and unornamented spider morphotypes. This work suggests that speciation may not be driven by single mechanisms, but rather by suites of mechanisms operating together. The discovery of a new ongoing speciation process in wolf spiders adds to the short list of systems that scientists can use to study how speciation happens, and suggests that there may be additional species to discover even in well-studied systems.</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>here is growing evidence that speciation can occur between populations that are not geographically isolated. The emergence of assortative mating is believed to be critical to this process, but how assortative mating arises in diverging populations is poorly understood. The wolf spider genus <i>Schizocosa</i> has become a model system for studying mechanisms of assortative mating. We conducted a series of experiments to identify the factors that control mate pair formation in a <i>Schizocosa</i> population that includes both ornamented and non-ornamented males. We show that the population also includes two previously unrecognized female phenotypes. One female phenotype mates mostly or exclusively with ornamented males, and the other mates mostly or exclusively with unornamented males. Assortative mating within these groups is maintained by differences in maturation time, microhabitat use, and female mate preference. We conclude that the population is not a single species as previously believed, but rather an incipient species pair with multiple overlapping mechanisms of reproductive isolation. The identification of a new incipient species pair in the well-studied and rapidly speciating <i>Schizocosa</i> clade presents new opportunities for the study of speciation without geographic isolation.</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, 19 Apr 2018 05:00:00 GMT “Sympatric parasites have similar host-associated, but asynchronous, patterns of diversification” http://amnat.org/an/newpapers/SepBell.html The DOI will be https://dx.doi.org/10.1086/698300 Because parasites are often restricted to just a few hosts with limited opportunities for dispersal, it has been thought that their evolutionary histories might mirror those of their hosts. Detailed investigations, however, are revealing more complex dynamics shaping parasite diversity. By comparing multiple parasites inhabiting the same hosts, researchers can shed light on the forces that drive parasite diversification. In this study, Bell and colleagues find evidence of distinct evolutionary histories in two parasites that infect the same hosts. They explore the genetic relationships within each of two species of roundworm parasites found in a diverse group of hosts, western North American chipmunks. Although both pinworm species have lineages primarily associated with one chipmunk species or a closely related group of chipmunk species, each roundworm species has a distinct evolutionary history. The unique histories are manifested as different relationships among the host associated genetic lineages, as well as distinct timing of divergence events within each parasite species. Comparative investigations such as this suggest that even when parasites share the same host and experience similar environments, different timing and patterns of evolutionary diversification can emerge. Abstract Parasitism is a common symbiotic interaction across diverse natural systems. Using a comparative evolutionary approach, we investigated the contributions of both host phylogeny and abiotic factors towards diversification of phylogenetically independent endoparasites that inhabit essentially the same physical space. We tested for host-parasite and parasite-parasite phylogenetic concordance in western North American chipmunks (Rodentia: Sciuridae) and two distantly related species of pinworms (Nematoda: Oxyurida). Deep structure in molecular phylogenies revealed signals of host-associated divergence in both parasite species, while shallower phylogeographic structure varied between the two parasites. This suggests that although these parasites experienced similar landscapes and cyclic climate processes, temporally distinctive diversification events were associated with differences in the initiation of their association with host lineages. When climate cycles initiate diversification, partially congruent, but asynchronous host-associated parasite phylogenies may emerge. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698300 </i></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698300">Read the Article</a></i></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>ecause parasites are often restricted to just a few hosts with limited opportunities for dispersal, it has been thought that their evolutionary histories might mirror those of their hosts. Detailed investigations, however, are revealing more complex dynamics shaping parasite diversity. By comparing multiple parasites inhabiting the same hosts, researchers can shed light on the forces that drive parasite diversification. </p><p>In this study, Bell and colleagues find evidence of distinct evolutionary histories in two parasites that infect the same hosts. They explore the genetic relationships within each of two species of roundworm parasites found in a diverse group of hosts, western North American chipmunks. Although both pinworm species have lineages primarily associated with one chipmunk species or a closely related group of chipmunk species, each roundworm species has a distinct evolutionary history. The unique histories are manifested as different relationships among the host associated genetic lineages, as well as distinct timing of divergence events within each parasite species. Comparative investigations such as this suggest that even when parasites share the same host and experience similar environments, different timing and patterns of evolutionary diversification can emerge. </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>arasitism is a common symbiotic interaction across diverse natural systems. Using a comparative evolutionary approach, we investigated the contributions of both host phylogeny and abiotic factors towards diversification of phylogenetically independent endoparasites that inhabit essentially the same physical space. We tested for host-parasite and parasite-parasite phylogenetic concordance in western North American chipmunks (Rodentia: Sciuridae) and two distantly related species of pinworms (Nematoda: Oxyurida). Deep structure in molecular phylogenies revealed signals of host-associated divergence in both parasite species, while shallower phylogeographic structure varied between the two parasites. This suggests that although these parasites experienced similar landscapes and cyclic climate processes, temporally distinctive diversification events were associated with differences in the initiation of their association with host lineages. When climate cycles initiate diversification, partially congruent, but asynchronous host-associated parasite phylogenies may emerge. </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, 19 Apr 2018 05:00:00 GMT “Matrix models of hierarchical demography: Linking group- and population-level dynamics in cooperative breeders” http://amnat.org/an/newpapers/AugBateman.html Read the Article Group matrix models shed light on population dynamics, Allee effects in meerkats and evolution of cooperative breeding For animal species that form social groups, living together can affect individuals’ chances of survival and reproduction. Whether the effects are positive or negative, an individual’s prospects tend to be limited within its group of birth, and many individuals leave in an effort to establish new breeding groups. As a result, understanding changes in population size for social species – several of which, such as African wild dogs and southern resident killer whales, are endangered – requires understanding of what goes on within groups and how individuals fare when they strike out on their own.New work by a team of researchers from Canada, the UK, and Switzerland combines theory and data to shed light on how these considerations play out for meerkats, a species of mongoose native to southern Africa. While past work has theorized that larger meerkat groups may produce more descendants each year than smaller groups (a phenomenon called the “Allee effect”), this new work indicates the opposite. Interestingly, dominant breeding females in larger groups do appear to produce more daughters that go on to breed. Overall, however, population growth seems to be maximized when meerkats form groups of intermediate size. This work presents a new way of analyzing data from social animals. The techniques used may prove valuable in exploring the evolution of sociality and in understanding fluctuations in populations of endangered or threatened species. Abstract For highly social species, population dynamics depend on hierarchical demography that links local processes, group dynamics, and population growth. Here, we describe a stage-structured matrix model of hierarchical demography, which provides a framework for understanding social influences on population change. Our approach accounts for dispersal and affords insight into population dynamics at multiple scales. The method has close parallels to integral projection models, but focuses on a discrete characteristic (group size). Using detailed long-term records for meerkats (Suricata suricatta), we apply our model to explore patterns of local density dependence and implications of group size for group and population growth. Taking into account dispersers, the model predicts a per-capita growth rate for social groups that declines with group size. It predicts that larger social groups should produce a greater number of new breeding groups; thus dominant breeding females (responsible for most reproduction) are likely to be more productive in larger groups. Considering the potential for future population growth, larger groups have the highest reproductive value, but per-capita reproductive value is maximized for individuals in smaller groups. Across a plausible range of dispersal conditions, meerkats&#39; long-run population growth rate is maximized when individuals form groups of intermediate size. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/698217"><i>Read the Article</i></a></p> <!-- <p><b><i><a href="https://dx.doi.org/10.1086/698217">Read the Article</a></i></b> </p> --> <p><b>Group matrix models shed light on population dynamics, Allee effects in meerkats and evolution of cooperative breeding </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>or animal species that form social groups, living together can affect individuals’ chances of survival and reproduction. Whether the effects are positive or negative, an individual’s prospects tend to be limited within its group of birth, and many individuals leave in an effort to establish new breeding groups. As a result, understanding changes in population size for social species – several of which, such as African wild dogs and southern resident killer whales, are endangered – requires understanding of what goes on within groups and how individuals fare when they strike out on their own.</p><p>New work by a team of researchers from Canada, the UK, and Switzerland combines theory and data to shed light on how these considerations play out for meerkats, a species of mongoose native to southern Africa. While past work has theorized that larger meerkat groups may produce more descendants each year than smaller groups (a phenomenon called the “Allee effect”), this new work indicates the opposite. Interestingly, dominant breeding females in larger groups do appear to produce more daughters that go on to breed. Overall, however, population growth seems to be maximized when meerkats form groups of intermediate size. </p><p>This work presents a new way of analyzing data from social animals. The techniques used may prove valuable in exploring the evolution of sociality and in understanding fluctuations in populations of endangered or threatened species. </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;">F</span>or highly social species, population dynamics depend on hierarchical demography that links local processes, group dynamics, and population growth. Here, we describe a stage-structured matrix model of hierarchical demography, which provides a framework for understanding social influences on population change. Our approach accounts for dispersal and affords insight into population dynamics at multiple scales. The method has close parallels to integral projection models, but focuses on a discrete characteristic (group size). Using detailed long-term records for meerkats (<i>Suricata suricatta</i>), we apply our model to explore patterns of local density dependence and implications of group size for group and population growth. Taking into account dispersers, the model predicts a per-capita growth rate for social groups that declines with group size. It predicts that larger social groups should produce a greater number of new breeding groups; thus dominant breeding females (responsible for most reproduction) are likely to be more productive in larger groups. Considering the potential for future population growth, larger groups have the highest reproductive value, but per-capita reproductive value is maximized for individuals in smaller groups. Across a plausible range of dispersal conditions, meerkats&#39; long-run population growth rate is maximized when individuals form groups of intermediate size.</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, 19 Apr 2018 05:00:00 GMT “On the interplay among ambient temperature, basal metabolic rate, and body mass” http://amnat.org/an/newpapers/OctNaya.html The DOI will be https://dx.doi.org/10.1086/698372 Researchers demonstrate that the effect of temperature on metabolic rate is highly dependent of the size of the sampled species Even though body mass in mammals ranges from a few grams to several tons, more than one-half of extant species weigh less than 100&nbsp;g. Clearly, the distribution of mammals’ body mass in nature is far from follow a normal distribution (panel A on figure at right). But could this highly skewed distribution of body size be affecting our overall impression about the role of different climatic and ecological factors that shape physiological evolution? To answer this question, two researchers from Uruguay (Daniel Naya and Hugo Naya) and one from Australia (Craig White) analyzed if the effect of ambient temperature on basal metabolic rate (BMR) change with the size of the species included in the analysis. And, yes, they found that it does! Specifically, these authors found that for species smaller than about 100&nbsp;g, BMR changed with both body mass and ambient temperature, while for species larger than about 100&nbsp;g BMR only changed with body mass (panel B on figure below). In other words, as authors conclude, a study analyzing all the 458 species in the dataset will affirm that the effect of temperature on BMR is markedly and highly significant, while a study analyzing only the 197 species larger than 100&nbsp;g will affirm that this effect is negligible and not significant. Asked about the implications of this result, Daniel Naya says, “To us, the work is relevant for at least two reasons. First, the specific result obtained for BMR is valuable by itself given the central role of this variable on current ecological and evolutionary theories. Second, and maybe more important, given that most organismal traits scale allometrically with body mass, it could be possible that our current impression of the effect of external factors shaping the evolution of phenotypic traits is hardly affected by the large number of small species in nature.” Abstract One of the most generalized conclusions arising from studies analyzing the ecological variation of energy metabolism in endotherms is the apparent negative correlation between ambient temperature and mass-independent basal metabolic rate (residual BMR). As a consequence, ambient temperature has been considered the most important external factor driving the evolution of residual BMR. It is not clear, however, if this relationship is size dependent, and artifacts such as the biased sampling of body masses in physiological data sets could cause us to overstate the ubiquity of the relationship. Accordingly, here we used published data on body mass (mb), BMR, and annual mean temperature (Tmean) for 458 mammal species (and/or subspecies) to examine the size-dependence of the relationship between temperature and BMR. We found a significant interaction between mb and Tmean as predictors of residual BMR, such that the effect of Tmean on residual BMR decreases as a function of mb. In line with this, the amount of residual variance in BMR explained by Tmean decreased with mb, from 20&nbsp;–&nbsp;30% at body sizes <&nbsp;100&nbsp;g to almost zero at body size >&nbsp;1,000&nbsp;g. These data suggest that our current understanding of the importance of broad-scale variation in ambient temperature as a driver of metabolic evolution in endotherms probably is affected by the large number of small species in both nature and physiological datasets. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698372 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698372">Read the Article</a></i> </p> --> <p><b>Researchers demonstrate that the effect of temperature on metabolic rate is highly dependent of the size of the sampled species </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;">E</span>ven though body mass in mammals ranges from a few grams to several tons, more than one-half of extant species weigh less than 100&nbsp;g. Clearly, the distribution of mammals&rsquo; body mass in nature is far from follow a normal distribution (panel A on figure at right). But could this highly skewed distribution of body size be affecting our overall impression about the role of different climatic and ecological factors that shape physiological evolution?</p> <p>To answer this question, two researchers from Uruguay (Daniel Naya and Hugo Naya) and one from Australia (Craig White) analyzed if the effect of ambient temperature on basal metabolic rate (BMR) change with the size of the species included in the analysis. And, yes, they found that it does! Specifically, these authors found that for species smaller than about 100&nbsp;g, BMR changed with both body mass and ambient temperature, while for species larger than about 100&nbsp;g BMR only changed with body mass (panel B on figure below). In other words, as authors conclude, a study analyzing all the 458 species in the dataset will affirm that the effect of temperature on BMR is markedly and highly significant, while a study analyzing only the 197 species larger than 100&nbsp;g will affirm that this effect is negligible and not significant.</p> <p>Asked about the implications of this result, Daniel Naya says, &ldquo;To us, the work is relevant for at least two reasons. First, the specific result obtained for BMR is valuable by itself given the central role of this variable on current ecological and evolutionary theories. Second, and maybe more important, given that most organismal traits scale allometrically with body mass, it could be possible that our current impression of the effect of external factors shaping the evolution of phenotypic traits is hardly affected by the large number of small species in nature.&rdquo;</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;">O</span>ne of the most generalized conclusions arising from studies analyzing the ecological variation of energy metabolism in endotherms is the apparent negative correlation between ambient temperature and mass-independent basal metabolic rate (residual BMR). As a consequence, ambient temperature has been considered the most important external factor driving the evolution of residual BMR. It is not clear, however, if this relationship is size dependent, and artifacts such as the biased sampling of body masses in physiological data sets could cause us to overstate the ubiquity of the relationship. Accordingly, here we used published data on body mass (<i>m<span style="bottom: -0.3em; font-size: 70%; position: relative;">b</span></i>), BMR, and annual mean temperature (Tmean) for 458 mammal species (and/or subspecies) to examine the size-dependence of the relationship between temperature and BMR. We found a significant interaction between <i>m<span style="bottom: -0.3em; font-size: 70%; position: relative;">b</span></i> and Tmean as predictors of residual BMR, such that the effect of Tmean on residual BMR decreases as a function of <i>m<span style="bottom: -0.3em; font-size: 70%; position: relative;">b</span></i>. In line with this, the amount of residual variance in BMR explained by Tmean decreased with <i>m<span style="bottom: -0.3em; font-size: 70%; position: relative;">b</span></i>, from 20&nbsp;&ndash;&nbsp;30% at body sizes &lt;&nbsp;100&nbsp;g to almost zero at body size &gt;&nbsp;1,000&nbsp;g. These data suggest that our current understanding of the importance of broad-scale variation in ambient temperature as a driver of metabolic evolution in endotherms probably is affected by the large number of small species in both nature and physiological datasets.</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, 18 Apr 2018 05:00:00 GMT