ASN RSS https://amnat.org/ Latest press releases and announcements from the ASN en-us Mon, 20 Aug 2018 05:00:00 GMT 60 “A comparative study of the role of sex-specific condition dependence in the evolution of sexually dimorphic traits” https://amnat.org/an/newpapers/DecRohner-A.html The DOI will be https://dx.doi.org/10.1086/700096 Abstract Sexual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should not only mirror the strength of sexual selection, but also the net viability costs and benefits of trait maintenance at equilibrium. As the ability of organisms to bear exaggerated traits will depend on their condition, more sexually dimorphic traits should also exhibit greater sex differences in condition dependence. While this has been demonstrated within species, similar patterns are expected across the phylogeny. We investigated this prediction within and across 11 (sub)species of sepsid flies with varying mating system. When estimating condition dependence for seven sexual and non-sexual traits that vary in their sexual dimorphism, we not only found a positive relationship between the sex difference in allometric slopes (our measure of condition dependence) and relative trait exaggeration within species, but also across species for those traits expected to be under sexual selection. Species with more pronounced male aggression had relatively larger and more condition-dependent male fore and mid legs. Our comparative study suggests a common genetic/developmental basis of sexual dimorphism and sex-specific plasticity that evolves across the phylogeny, and that the evolution of size consistently alters scaling relationships and thus contributes to the allometric variation of sexual armaments or ornaments in animals. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700096 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700096">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;">S</span>exual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should not only mirror the strength of sexual selection, but also the net viability costs and benefits of trait maintenance at equilibrium. As the ability of organisms to bear exaggerated traits will depend on their condition, more sexually dimorphic traits should also exhibit greater sex differences in condition dependence. While this has been demonstrated within species, similar patterns are expected across the phylogeny. We investigated this prediction within and across 11 (sub)species of sepsid flies with varying mating system. When estimating condition dependence for seven sexual and non-sexual traits that vary in their sexual dimorphism, we not only found a positive relationship between the sex difference in allometric slopes (our measure of condition dependence) and relative trait exaggeration within species, but also across species for those traits expected to be under sexual selection. Species with more pronounced male aggression had relatively larger and more condition-dependent male fore and mid legs. Our comparative study suggests a common genetic/developmental basis of sexual dimorphism and sex-specific plasticity that evolves across the phylogeny, and that the evolution of size consistently alters scaling relationships and thus contributes to the allometric variation of sexual armaments or ornaments in animals. </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, 16 Aug 2018 05:00:00 GMT “Genetic quality affects the rate of male and female reproductive ageing differently in Drosophila melanogaster” https://amnat.org/an/newpapers/DecBrengdahl.html The DOI will be https://dx.doi.org/10.1086/700117 Genetic quality affects the rate of male and female reproductive ageing differently in Drosophila melanogaster Why males and females of many species display different rates of ageing is puzzling and may hold the key to explain the enormous variation in ageing found among species. A team of researchers from Linköping University in Sweden has investigated the hypothesis that sex differences in reproductive ageing result from the sexes investing different amounts of their energy budgets into current reproduction and maintaining their bodies. To test this hypothesis, they varied the genetic quality of male and female fruit flies through the number of deleterious mutations they expressed, with consequences for how efficiently they could compete over food resources and convert these into usable energy. In response to the manipulation, the authors find that the pace of male reproductive ageing is unaltered by genetic quality, but that high-quality females show considerably slower reproductive ageing compared to low-quality females. These results suggest that high-quality females invest relatively more energy than low-quality females into maintaining their bodies and the opportunity to reproduce also later in life, while males, independently of their quality, focus on current reproduction. These results fit with the general view that males and females are selected to peruse different strategies to maximize reproductive success; as a consequence, males face fierce competition over access to females, and female production of eggs and offspring is primarily limited by access to resources. Abstract Males and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade-off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive ageing. Here we investigate if reproductive ageing and lifespan respond to condition differently in male and female Drosophila melanogaster, as predicted if sexual selection has shaped male and female resource allocation patterns. We manipulate condition through genetic quality, by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male than female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive ageing between the sexes in low condition, but in high condition reproductive ageing is relatively faster in males. No corresponding sex-specific change was found for lifespan. The sex difference in reproductive ageing appearing in high condition was due specifically to a decreased ageing rate in females, rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more towards somatic maintenance than males. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700117 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700117">Read the Article</a></i> </p> --> <p><b>Genetic quality affects the rate of male and female reproductive ageing differently in <i>Drosophila melanogaster</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;">W</span>hy males and females of many species display different rates of ageing is puzzling and may hold the key to explain the enormous variation in ageing found among species. A team of researchers from Linköping University in Sweden has investigated the hypothesis that sex differences in reproductive ageing result from the sexes investing different amounts of their energy budgets into current reproduction and maintaining their bodies. To test this hypothesis, they varied the genetic quality of male and female fruit flies through the number of deleterious mutations they expressed, with consequences for how efficiently they could compete over food resources and convert these into usable energy. In response to the manipulation, the authors find that the pace of male reproductive ageing is unaltered by genetic quality, but that high-quality females show considerably slower reproductive ageing compared to low-quality females. These results suggest that high-quality females invest relatively more energy than low-quality females into maintaining their bodies and the opportunity to reproduce also later in life, while males, independently of their quality, focus on current reproduction. These results fit with the general view that males and females are selected to peruse different strategies to maximize reproductive success; as a consequence, males face fierce competition over access to females, and female production of eggs and offspring is primarily limited by access to resources. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ales and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade-off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive ageing. Here we investigate if reproductive ageing and lifespan respond to condition differently in male and female <i>Drosophila melanogaster</i>, as predicted if sexual selection has shaped male and female resource allocation patterns. We manipulate condition through genetic quality, by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male than female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive ageing between the sexes in low condition, but in high condition reproductive ageing is relatively faster in males. No corresponding sex-specific change was found for lifespan. The sex difference in reproductive ageing appearing in high condition was due specifically to a decreased ageing rate in females, rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more towards somatic maintenance than males. </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, 16 Aug 2018 05:00:00 GMT “Natural selection on anti-helminth antibodies in a wild mammal population” https://amnat.org/an/newpapers/DecSparks.html The DOI will be https://dx.doi.org/10.1086/700115 Natural selection on immune responses vary across demographic groups but not environments in a wild mammal population The immune system is crucial in defending individuals against a multitude of parasites, and consequently effective immune responses are expected to be under selection. However, studies in the wild have shown there is considerable variation in immune responses between individuals. One explanation for the maintenance of such variability is that immune responses are energetically costly and this results in trade-offs with other traits such as growth and reproduction. The costs and benefits of immune responses may also vary by age and sex of the individual as well as their environment, but few studies have investigated this.Using data from a long-term individual-based study of wild Soay sheep living unmanaged in the St&nbsp;Kilda archipelago, the authors measured anti-parasite antibodies (IgA, IgE, IgG) in blood samples collected from sheep caught over a 25-year period. They then investigated whether these antibodies were associated with parasite fecal egg counts (a measure of parasite burden), weight, over-winter survival, and breeding success. Contrary to predictions, they did not find strong evidence for environment-dependent selection or costs associated with reproduction. The authors did find that high antibody levels predicted lower parasite egg counts and over-winter survival; however, this was dependent on the antibody isotype as well as the age and sex of the individual. Lambs with higher IgA levels had lower parasite egg counts but none of the antibodies were associated with over-winter survival. In contrast, adults with higher IgG levels had lower parasite egg counts and adult females with higher IgG levels were more likely to survive over winter. These results highlight the complexity of natural selection on immune traits in the wild and suggest that patterns of selection are unlikely to generalize across different immune measures or host demographic groups. Abstract An effective immune response is expected to confer fitness benefits through improved resistance to parasites but also incur energetic costs which negatively impact fitness-related traits such as reproduction. The fitness costs and benefits of an immune response are likely to depend on host age, sex, and levels of parasite exposure. Few studies have examined the full extent to which patterns of natural selection on immune phenotypes vary across demographic groups and environments in the wild. Here, we assessed natural selection on plasma levels of three functionally distinct isotypes (IgA, IgE and IgG) of antibodies against a prevalent nematode parasite measured in a wild Soay sheep population over 25 years. We found little support for environment-dependent selection or reproductive costs. However, antibody levels were negatively associated with parasite egg counts and positively associated with subsequent survival, albeit in a highly age- and isotype-dependent manner. Raised levels of anti-parasite IgA best predicted reduced egg counts but this did not predict survival in lambs. In adults increased anti-parasite IgG predicted reduced egg counts and in adult females IgG levels also positively predicted over-winter survival. Our results highlight the potential importance of age- and sex-dependent selection on immune phenotypes in nature, and show that patterns of selection can vary even amongst functionally-related immune markers. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700115 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700115">Read the Article</a></i> </p> --> <p><b>Natural selection on immune responses vary across demographic groups but not environments in a wild mammal population </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;">T</span>he immune system is crucial in defending individuals against a multitude of parasites, and consequently effective immune responses are expected to be under selection. However, studies in the wild have shown there is considerable variation in immune responses between individuals. One explanation for the maintenance of such variability is that immune responses are energetically costly and this results in trade-offs with other traits such as growth and reproduction. The costs and benefits of immune responses may also vary by age and sex of the individual as well as their environment, but few studies have investigated this.</p><p>Using data from a long-term individual-based study of wild Soay sheep living unmanaged in the St&nbsp;Kilda archipelago, the authors measured anti-parasite antibodies (IgA, IgE, IgG) in blood samples collected from sheep caught over a 25-year period. They then investigated whether these antibodies were associated with parasite fecal egg counts (a measure of parasite burden), weight, over-winter survival, and breeding success. Contrary to predictions, they did not find strong evidence for environment-dependent selection or costs associated with reproduction. The authors did find that high antibody levels predicted lower parasite egg counts and over-winter survival; however, this was dependent on the antibody isotype as well as the age and sex of the individual. Lambs with higher IgA levels had lower parasite egg counts but none of the antibodies were associated with over-winter survival. In contrast, adults with higher IgG levels had lower parasite egg counts and adult females with higher IgG levels were more likely to survive over winter. These results highlight the complexity of natural selection on immune traits in the wild and suggest that patterns of selection are unlikely to generalize across different immune measures or host demographic 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;">A</span>n effective immune response is expected to confer fitness benefits through improved resistance to parasites but also incur energetic costs which negatively impact fitness-related traits such as reproduction. The fitness costs and benefits of an immune response are likely to depend on host age, sex, and levels of parasite exposure. Few studies have examined the full extent to which patterns of natural selection on immune phenotypes vary across demographic groups and environments in the wild. Here, we assessed natural selection on plasma levels of three functionally distinct isotypes (IgA, IgE and IgG) of antibodies against a prevalent nematode parasite measured in a wild Soay sheep population over 25 years. We found little support for environment-dependent selection or reproductive costs. However, antibody levels were negatively associated with parasite egg counts and positively associated with subsequent survival, albeit in a highly age- and isotype-dependent manner. Raised levels of anti-parasite IgA best predicted reduced egg counts but this did not predict survival in lambs. In adults increased anti-parasite IgG predicted reduced egg counts and in adult females IgG levels also positively predicted over-winter survival. Our results highlight the potential importance of age- and sex-dependent selection on immune phenotypes in nature, and show that patterns of selection can vary even amongst functionally-related immune markers. </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, 16 Aug 2018 05:00:00 GMT “Evolutionary responses to conditionality in species interactions across environmental gradients” https://amnat.org/an/newpapers/DecOBrien.html The DOI will be https://dx.doi.org/10.1086/700118 (Co)evolutionary outcomes of conditionality in biotic interactions: prediction, experiment design, and statistical test While we often characterize species interactions as being either beneficial or detrimental to the participants, in reality, the fitness outcomes of interactions can vary substantially, especially across environments (a.k.a. conditionality). A well-known example of such conditionality is the outcome of interactions between plants in the high alpine, where sites are cold, dry, and windy, and the substrate is unstable. Here, plants promote each others’ growth by buffering temperatures, wind, and soil erosion, but when the same species are neighbors lower on the same mountain slope, they compete with one another for resources. Ecological theory suggests that physical stress or the lack of availability of resources can determine the outcome of interactions: species interactions may become more positive (shift to mutually beneficial outcomes) under stressful conditions and become more negative when resources are freely available or when the physical environment is benign. Environmentally driven variation in interaction outcomes may also shape evolutionary responses of species. For example, selection may favor new mutations in interacting species that increase investment in beneficial interactions (mutualisms) at stressful ends of environmental gradients, leading to mutually beneficial coevolution between interacting partners. On the other hand, when stress is minimal or non-existent, one might predict no coevolution, or possibly antagonistic coevolution between interacting partners. Here, the authors develop and demonstrate new methods to empirically test these predictions. Insights gained from these models can be applied to a wide range of species interactions and conditional outcomes. Understanding these ecological and evolutionary forces will become increasingly important as species find themselves in novel interactions and physical contexts with climate change. Abstract The outcomes of many species interactions are conditional on the environments in which they occur. Often, interactions grade from being more positive under stressful or low-resource conditions to more antagonistic or neutral under benign conditions. Here, we take predictions of two well-supported ecological theories on conditionality—limiting resources models and the stress gradient hypothesis—and combine them with those from the geographic mosaic theory of coevolution (GMTC) to generate predictions for systematic patterns of adaptation and co-adaptation between partners along abiotic gradients. When interactions become more positive in stressful environments, mutations that increase fitness in one partner may also increase fitness in the other; because fitnesses are aligned, selection should favor greater mutualistic adaptation and co-adaptation between interacting species in stressful ends of environmental gradients. As a corollary, in benign environments, antagonistic co-adaptation could result in Red Queen or arms-race dynamics, or reduction of antagonism through character displacement and niche partitioning. Here, we distinguish between generally mutualistic or antagonistic adaptation (i.e., mutations in one partner that have similar effects across multiple populations of the other), versus specific adaptations to sympatric partners (local adaptation), which can occur either alone or simultaneously. We then outline the kinds of data required to test these predictions, develop experimental designs and statistical methods, and demonstrate these using simulations based on GMTC models. Our methods can be applied to a range of conditional outcomes, and may also be useful in assisted translocation approaches in the face of climate change. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700118 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700118">Read the Article</a></i> </p> --> <p><b>(Co)evolutionary outcomes of conditionality in biotic interactions: prediction, experiment design, and statistical test </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>hile we often characterize species interactions as being either beneficial or detrimental to the participants, in reality, the fitness outcomes of interactions can vary substantially, especially across environments (a.k.a. conditionality). A well-known example of such conditionality is the outcome of interactions between plants in the high alpine, where sites are cold, dry, and windy, and the substrate is unstable. Here, plants promote each others’ growth by buffering temperatures, wind, and soil erosion, but when the same species are neighbors lower on the same mountain slope, they compete with one another for resources. Ecological theory suggests that physical stress or the lack of availability of resources can determine the outcome of interactions: species interactions may become more positive (shift to mutually beneficial outcomes) under stressful conditions and become more negative when resources are freely available or when the physical environment is benign. </p> <p>Environmentally driven variation in interaction outcomes may also shape evolutionary responses of species. For example, selection may favor new mutations in interacting species that increase investment in beneficial interactions (mutualisms) at stressful ends of environmental gradients, leading to mutually beneficial coevolution between interacting partners. On the other hand, when stress is minimal or non-existent, one might predict no coevolution, or possibly antagonistic coevolution between interacting partners. </p> <p>Here, the authors develop and demonstrate new methods to empirically test these predictions. Insights gained from these models can be applied to a wide range of species interactions and conditional outcomes. Understanding these ecological and evolutionary forces will become increasingly important as species find themselves in novel interactions and physical contexts with climate change. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he outcomes of many species interactions are conditional on the environments in which they occur. Often, interactions grade from being more positive under stressful or low-resource conditions to more antagonistic or neutral under benign conditions. Here, we take predictions of two well-supported ecological theories on conditionality&mdash;limiting resources models and the stress gradient hypothesis&mdash;and combine them with those from the geographic mosaic theory of coevolution (GMTC) to generate predictions for systematic patterns of adaptation and co-adaptation between partners along abiotic gradients. When interactions become more positive in stressful environments, mutations that increase fitness in one partner may also increase fitness in the other; because fitnesses are aligned, selection should favor greater mutualistic adaptation and co-adaptation between interacting species in stressful ends of environmental gradients. As a corollary, in benign environments, antagonistic co-adaptation could result in Red Queen or arms-race dynamics, or reduction of antagonism through character displacement and niche partitioning. Here, we distinguish between generally mutualistic or antagonistic adaptation (i.e., mutations in one partner that have similar effects across multiple populations of the other), versus specific adaptations to sympatric partners (local adaptation), which can occur either alone or simultaneously. We then outline the kinds of data required to test these predictions, develop experimental designs and statistical methods, and demonstrate these using simulations based on GMTC models. Our methods can be applied to a range of conditional outcomes, and may also be useful in assisted translocation approaches in the face of climate change. </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, 14 Aug 2018 05:00:00 GMT “Eco-evolutionary dynamics in metacommunities: ecological inheritance, helping within- and harming between-species” https://amnat.org/an/newpapers/DecMullon-A.html The DOI will be https://dx.doi.org/10.1086/700094 Abstract Understanding selection on intra- and inter-specific interactions that take place in dispersal-limited communities is a challenge for ecology and evolutionary biology. The problem is that local demographic stochasticity generates eco-evolutionary dynamics that are generally too complicated to make tractable analytical investigations. Here, we circumvent this problem by approximating the selection gradient on a quantitative trait that influences local community dynamics, assuming that such dynamics are deterministic with a stable fixed point. We nonetheless incorporate unavoidable kin selection effects arising from demographic stochasticity. Our approximation reveals that selection depends on how an individual expressing a trait-change influences: (1) its own fitness and the fitness of its current relatives; and (2) the fitness of its downstream relatives through modifications of local ecological conditions (i.e., through ecological inheritance). Mathematically, the effects of ecological inheritance on selection are captured by dispersal-limited versions of press-perturbations of community ecology. We use our approximation to investigate the evolution of helping within- and harming between-species when these behaviours influence demography. We find that altruistic helping evolves more readily when intra-specific competition is for material resources rather than for space because in this case, the costs of kin competition tend to paid by downstream relatives. Similarly, altruistic harming between species evolves when it alleviates downstream relatives from inter-specific competition. Beyond these examples, our approximation can help better understand the influence of ecological inheritance on a variety of eco-evolutionary dynamics in metacommunities, from consumer-resource and predator-prey coevolution to selection on mating systems with demographic feedbacks. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700094 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700094">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;">U</span>nderstanding selection on intra- and inter-specific interactions that take place in dispersal-limited communities is a challenge for ecology and evolutionary biology. The problem is that local demographic stochasticity generates eco-evolutionary dynamics that are generally too complicated to make tractable analytical investigations. Here, we circumvent this problem by approximating the selection gradient on a quantitative trait that influences local community dynamics, assuming that such dynamics are deterministic with a stable fixed point. We nonetheless incorporate unavoidable kin selection effects arising from demographic stochasticity. Our approximation reveals that selection depends on how an individual expressing a trait-change influences: (1) its own fitness and the fitness of its current relatives; and (2) the fitness of its downstream relatives through modifications of local ecological conditions (i.e., through ecological inheritance). Mathematically, the effects of ecological inheritance on selection are captured by dispersal-limited versions of press-perturbations of community ecology. We use our approximation to investigate the evolution of helping within- and harming between-species when these behaviours influence demography. We find that altruistic helping evolves more readily when intra-specific competition is for material resources rather than for space because in this case, the costs of kin competition tend to paid by downstream relatives. Similarly, altruistic harming between species evolves when it alleviates downstream relatives from inter-specific competition. Beyond these examples, our approximation can help better understand the influence of ecological inheritance on a variety of eco-evolutionary dynamics in metacommunities, from consumer-resource and predator-prey coevolution to selection on mating systems with demographic feedbacks. </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, 14 Aug 2018 05:00:00 GMT “The cost of being big: local competition, importance of dispersal, and experimental evolution of reversal to unicellularity” https://amnat.org/an/newpapers/DecRebolleda.html The DOI will be https://dx.doi.org/10.1086/700095 Multicellularity (staying-together) did not evolve on land: why? Potentially high competition and dispersal constraints Multicellularity has evolved independently multiple times, and in many cases, unicellularity has evolved again from multicellular ancestors. Cancers, for example, are evolutionary reversals to unicellularity, in which cells no longer act as part of a larger coordinated whole, but as autonomous entities. Research in multicellularity has focused on these challenges of cooperation. However, cooperation and conflict are not the only challenges faced by multicellular organisms. The appearance of multicellular life is one of the biggest increases in size in the fossil record, and being big comes with challenges of its own. In this study María Rebolleda-Gómez and Michael Travisano evaluated the costs of multicellularity in recently evolved multicellular phenotypes that evolved in the laboratory as a result of selection for increased size. Combining growth assays, competition experiments, computer simulations, and experimental evolution, they show that costs of resource acquisition and local competition can readily lead to the evolution of reversals to single cells. These costs depend on the size of the multicellular organisms, their ability to disperse and the distribution of resources. In liquid media—where resources are evenly distributed—multicellularity imposes spatial structure and internal cells have less space and/or fewer resources for growth. In contrast, on plates, despite similar growth between multicellular and unicellular isolates (because single cells cannot move away from each other during growth), multicellular isolates are rapidly outcompeted by their unicellular ancestor. In this environment, every time a subset of the population is established in a new plate, unicellular isolates can disperse better and are able to take advantage of more resources. Multicellular individuals are comprised of multiple cells that all compete for the same resources. As a result, selection on plates but not on liquid leads to rapid reversals to unicellularity. Multicellularity has evolved independently more than 20 times with very different consequences in each of these transitions. A better understanding of the physical and ecological consequences of the morphological changes during the evolution of multicellularity can help us understand this multicellular diversity. Local competition and dispersal limitations may be among the reasons why most multicellular forms that develop through cells staying together have evolved in water, whereas most of the land origins of multicellularity involve single cells coming together temporarily (and often as a means for dispersal). Multicellularity transformed the physical space in which cells interact and this paper provides insight into the physical, ecological, and evolutionary limitations of this major transition. Abstract Multicellularity provides multiple benefits. Nonetheless, unicellularity is ubiquitous and there have been multiple cases of evolutionary reversal to a unicellular organization. In this paper, we explore some of the costs of multicellularity as well as the possibility and dynamics of evolutionary reversals to unicellularity. We hypothesize that recently evolved multicellular organisms would face a high cost of increased competition for local resources in spatially structured environments because of larger size and increased cell densities. To test this hypothesis we conducted competition assays, computer simulations, and selection experiments using isolates of Saccharomyces cerevisiae that recently evolved multicellularity. In well-mixed environments, multicellular isolates had lower growth rates relative to their unicellular ancestor due to limitations of space and resource acquisition. In structured environments with localized resources, cells in both multicellular and unicellular isolates grew at a similar rate. Despite similar growth, higher local density of cells in multicellular groups led to increased competition and higher fitness costs in spatially structured environments. In structured environments all of the multicellular isolates rapidly evolved a predominantly unicellular life cycle, while in well-mixed environments reversal was more gradual. Taken together, these results suggest that a lack of dispersal, leading to higher local competition, might have been one of the main constraints in the evolution of early multicellular forms. El costo de ser grande: competencia local, importancia de dispersión y evolución experimental de reversiones a unicelularidad Aunque la multicelularidad provee diversos beneficios, la vida unicelular es ubicua y ha habido varios casos de reversiones evolutivas a una forma de organización unicelular. En este artículo exploramos algunos de los costos de la multicelularidad, así como la posibilidad y las dinámicas de reversión a la unicelularidad. Nuestra hipótesis es que, en ambientes con estructura espacial, organismos que evolucionaron multicellularidad recientemente, van a enfrentar mayores costos asociados con una mayor competencia por los recursos locales, debido a que los organismos multicelulares tienen un mayor tamaño y mayores densidades celulares. Para evaluar esta hipótesis, realizamos ensayos de competencia, simulaciones de computadora y evolución experimental con aislados de Saccharomyces cerevisiae que recientemente evolucionaron fenotípos multicelulares. En ambientes con agitación constante, los aislados multicellulares tienen menores tasas de crecimiento que su ancestro unicelular debido a limitaciones de espacio y adqusición de recursos. En ambientes espacialmente estructurados, con recursos localizados, las células de aislados unicelulares y multicelulares crecen a la misma velocidad. Sin embargo, la mayor densidad local de células en grupos multicelulares resultó en mayor competencia y costos de adecuación en ambientes con estructura espacial. En estos ambientes con recursos localizados todos los aislados multicelulares evolucionaron un ciclo de vida principalmente unicelular, mientras que en ambientes con una distribución más homogénea la reversión a unicelularidad fue mucho más gradual. Juntos, estos resultados sugieren que la falta de dispersión, que resulta en una mayor competencia, puede haber sido una de las principales restricciones en la evolución de las primeras formas multicelulares. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700095 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700095">Read the Article</a></i> </p> --> <p><b>Multicellularity (staying-together) did not evolve on land: why? Potentially high competition and dispersal constraints </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>ulticellularity has evolved independently multiple times, and in many cases, unicellularity has evolved again from multicellular ancestors. Cancers, for example, are evolutionary reversals to unicellularity, in which cells no longer act as part of a larger coordinated whole, but as autonomous entities. Research in multicellularity has focused on these challenges of cooperation. However, cooperation and conflict are not the only challenges faced by multicellular organisms. The appearance of multicellular life is one of the biggest increases in size in the fossil record, and being big comes with challenges of its own. </p><p>In this study María Rebolleda-Gómez and Michael Travisano evaluated the costs of multicellularity in recently evolved multicellular phenotypes that evolved in the laboratory as a result of selection for increased size. Combining growth assays, competition experiments, computer simulations, and experimental evolution, they show that costs of resource acquisition and local competition can readily lead to the evolution of reversals to single cells. These costs depend on the size of the multicellular organisms, their ability to disperse and the distribution of resources. In liquid media—where resources are evenly distributed—multicellularity imposes spatial structure and internal cells have less space and/or fewer resources for growth. In contrast, on plates, despite similar growth between multicellular and unicellular isolates (because single cells cannot move away from each other during growth), multicellular isolates are rapidly outcompeted by their unicellular ancestor. In this environment, every time a subset of the population is established in a new plate, unicellular isolates can disperse better and are able to take advantage of more resources. Multicellular individuals are comprised of multiple cells that all compete for the same resources. As a result, selection on plates but not on liquid leads to rapid reversals to unicellularity. </p><p>Multicellularity has evolved independently more than 20 times with very different consequences in each of these transitions. A better understanding of the physical and ecological consequences of the morphological changes during the evolution of multicellularity can help us understand this multicellular diversity. Local competition and dispersal limitations may be among the reasons why most multicellular forms that develop through cells staying together have evolved in water, whereas most of the land origins of multicellularity involve single cells coming together temporarily (and often as a means for dispersal). Multicellularity transformed the physical space in which cells interact and this paper provides insight into the physical, ecological, and evolutionary limitations of this major transition. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ulticellularity provides multiple benefits. Nonetheless, unicellularity is ubiquitous and there have been multiple cases of evolutionary reversal to a unicellular organization. In this paper, we explore some of the costs of multicellularity as well as the possibility and dynamics of evolutionary reversals to unicellularity. We hypothesize that recently evolved multicellular organisms would face a high cost of increased competition for local resources in spatially structured environments because of larger size and increased cell densities. To test this hypothesis we conducted competition assays, computer simulations, and selection experiments using isolates of <i>Saccharomyces cerevisiae</i> that recently evolved multicellularity. In well-mixed environments, multicellular isolates had lower growth rates relative to their unicellular ancestor due to limitations of space and resource acquisition. In structured environments with localized resources, cells in both multicellular and unicellular isolates grew at a similar rate. Despite similar growth, higher local density of cells in multicellular groups led to increased competition and higher fitness costs in spatially structured environments. In structured environments all of the multicellular isolates rapidly evolved a predominantly unicellular life cycle, while in well-mixed environments reversal was more gradual. Taken together, these results suggest that a lack of dispersal, leading to higher local competition, might have been one of the main constraints in the evolution of early multicellular forms. </p> <h4>El costo de ser grande: competencia local, importancia de dispersión y evolución experimental de reversiones a unicelularidad</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>unque la multicelularidad provee diversos beneficios, la vida unicelular es ubicua y ha habido varios casos de reversiones evolutivas a una forma de organización unicelular. En este artículo exploramos algunos de los costos de la multicelularidad, así como la posibilidad y las dinámicas de reversión a la unicelularidad. Nuestra hipótesis es que, en ambientes con estructura espacial, organismos que evolucionaron multicellularidad recientemente, van a enfrentar mayores costos asociados con una mayor competencia por los recursos locales, debido a que los organismos multicelulares tienen un mayor tamaño y mayores densidades celulares. Para evaluar esta hipótesis, realizamos ensayos de competencia, simulaciones de computadora y evolución experimental con aislados de <i>Saccharomyces cerevisiae</i> que recientemente evolucionaron fenotípos multicelulares. En ambientes con agitación constante, los aislados multicellulares tienen menores tasas de crecimiento que su ancestro unicelular debido a limitaciones de espacio y adqusición de recursos. En ambientes espacialmente estructurados, con recursos localizados, las células de aislados unicelulares y multicelulares crecen a la misma velocidad. Sin embargo, la mayor densidad local de células en grupos multicelulares resultó en mayor competencia y costos de adecuación en ambientes con estructura espacial. En estos ambientes con recursos localizados todos los aislados multicelulares evolucionaron un ciclo de vida principalmente unicelular, mientras que en ambientes con una distribución más homogénea la reversión a unicelularidad fue mucho más gradual. Juntos, estos resultados sugieren que la falta de dispersión, que resulta en una mayor competencia, puede haber sido una de las principales restricciones en la evolución de las primeras formas multicelulares. </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, 14 Aug 2018 05:00:00 GMT “Considerations used by desert isopods to assess scorpion predation risk” https://amnat.org/an/newpapers/NovZaguri.html The DOI will be https://dx.doi.org/10.1086/699840 Assessing the risk assessment – which predatory cues and in what context will justify an anti-predatory response? “The world is a dangerous place to live,” wrote Albert Einstein. This is most likely what desert isopods think every morning when leaving the safety of their family burrows to forage in a landscape full of threats. Trying to reveal how prey distinguish between safe and dangerous areas is a major experimental challenge because it requires inferring sensory abilities and cognitive decisions from their behavioral reactions. In this paper, Zaguri, Zohar, and Hawlena from the Ecostress lab at the Hebrew University of Jerusalem have explored how isopods assess the threat of golden Israeli scorpion predation in the central Negev desert. They introduced different combinations of signals that scorpions leave behind to the isopod natural habitat, and meticulously measured the isopods’ behavioral responses to these signals upon first encountering them. Isopods can identify the smell of a scorpion but respond to them only when this smell is associated with other odors or excavated soil mounds that imply an active scorpion burrow. This risk assessment process is efficient because golden scorpions hunt isopods only from the depth of the burrow. Simultaneous presence of different predator cues provoked graded defense reaction, possibly reflecting an additive increase in risk estimation. Our results suggest that isopods can modify their risk estimation based on the context in which the cue is perceived. Abstract Animals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use complex risk assessment process that estimates risks and weigh costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (Hemilepistus reaumuri) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions upon first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated-soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow, or when they lack data to refute this possibility. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699840 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699840">Read the Article</a></i> </p> --> <p><b>Assessing the risk assessment &ndash; which predatory cues and in what context will justify an anti-predatory response? </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">“T</span>he world is a dangerous place to live,” wrote Albert Einstein. This is most likely what desert isopods think every morning when leaving the safety of their family burrows to forage in a landscape full of threats. Trying to reveal how prey distinguish between safe and dangerous areas is a major experimental challenge because it requires inferring sensory abilities and cognitive decisions from their behavioral reactions. In this paper, Zaguri, Zohar, and Hawlena from the Ecostress lab at the Hebrew University of Jerusalem have explored how isopods assess the threat of golden Israeli scorpion predation in the central Negev desert. They introduced different combinations of signals that scorpions leave behind to the isopod natural habitat, and meticulously measured the isopods’ behavioral responses to these signals upon first encountering them. Isopods can identify the smell of a scorpion but respond to them only when this smell is associated with other odors or excavated soil mounds that imply an active scorpion burrow. This risk assessment process is efficient because golden scorpions hunt isopods only from the depth of the burrow. Simultaneous presence of different predator cues provoked graded defense reaction, possibly reflecting an additive increase in risk estimation. Our results suggest that isopods can modify their risk estimation based on the context in which the cue is perceived. </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>nimals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use complex risk assessment process that estimates risks and weigh costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (<i>Hemilepistus reaumuri</i>) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions upon first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated-soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow, or when they lack data to refute this possibility. </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, 01 Aug 2018 05:00:00 GMT “Atypical flowers can be as profitable as typical hummingbird flowers” https://amnat.org/an/newpapers/NovWaser.html The DOI will be https://dx.doi.org/10.1086/699836 Don’t ignore the unexpected! Our example: visits to “atypical” flowers can be surprisingly profitable for hummingbirds What is a hummingbird flower? It may not be what you expect! Nick Waser and Mary Price began to learn this lesson while camping as graduate students in the 1970s. They were repeatedly surprised to see hummingbirds systematically visiting flowers that lacked the characteristic features of “typical” hummingbird flowers. Curious about whether the birds were being “duped” by these flowers, they began to measure foraging rates of the birds and the energy content of nectar provided by a variety of atypical and typical flowers and to compare that with what was known about the birds’ energetic needs. They continued their observations opportunistically over the next four decades at various locations throughout the southwestern USA, eventually enlisting help from younger colleague Paul CaraDonna. The three ecologists discovered that the birds are making no mistake in their behavior—the atypical flowers often are just as energetically profitable as typical red, tubular hummingbird flowers. In fact, the nectar rewards of atypical flowers in some cases appear to be adequate by themselves to support the high metabolic needs of hummingbirds throughout a 24-hour period. What these observations tell us is that atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly scarce in suitable resources. They also emphasize what can be gained by attending to the unexpected. Abstract In western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of “hummingbird flowers”. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-hr metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699836 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699836">Read the Article</a></i> </p> --> <p><b>Don’t ignore the unexpected! Our example: visits to “atypical” flowers can be surprisingly profitable for hummingbirds </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>hat is a hummingbird flower? It may not be what you expect! Nick Waser and Mary Price began to learn this lesson while camping as graduate students in the 1970s. They were repeatedly surprised to see hummingbirds systematically visiting flowers that lacked the characteristic features of “typical” hummingbird flowers. Curious about whether the birds were being “duped” by these flowers, they began to measure foraging rates of the birds and the energy content of nectar provided by a variety of atypical and typical flowers and to compare that with what was known about the birds’ energetic needs. They continued their observations opportunistically over the next four decades at various locations throughout the southwestern USA, eventually enlisting help from younger colleague Paul CaraDonna. The three ecologists discovered that the birds are making no mistake in their behavior—the atypical flowers often are just as energetically profitable as typical red, tubular hummingbird flowers. In fact, the nectar rewards of atypical flowers in some cases appear to be adequate by themselves to support the high metabolic needs of hummingbirds throughout a 24-hour period. What these observations tell us is that atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly scarce in suitable resources. They also emphasize what can be gained by attending to the unexpected. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of “hummingbird flowers”. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-hr metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected. </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, 25 Jul 2018 05:00:00 GMT “Early and adult social environments shape sex-specific actuarial senescence patterns in a cooperative breeder” https://amnat.org/an/newpapers/OctVBerger.html The DOI will be https://dx.doi.org/10.1086/699513 Individuals from social species typically show a slow growth, a delayed age at first reproduction, and a long life compared to individuals from non-social species with similar size. In cooperative breeders such as meerkats, wolves, or beavers, helpers assist a dominant pair to raise pups. So far, whether sociality influences actuarial senescence (i.e. the age-specific decrease in survival) remains unknown, although helpers take care of pups, which contributes to decreasing the amount of energy that dominants allocate to parental care. We can thus expect that the presence of helpers delays and slows down senescence. A team of researchers from the University of Lyon combined their expertise in demography and sociality to test this expectation in a cooperative breeder, the Alpine marmot. They found that the beneficial effect of helpers depended on the timing of the help. Having helpers as adult slowed down much senescence more than having helpers early in life. Moreover, the benefits of being helped was sex-specific, with actuarial senescence reduced in females but not in males. Their work emphasizes that sociality influences senescence but that the benefits in terms of reduced senescence are sex-specific and depend on when help occurs. These findings have important theoretical implications on current evolutionary theories of ageing, which do not include yet a social component. Abstract Sociality modulates life history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided, and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex-specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among dominants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence, but acts differently between sexes and life stages. Résumé : Les environnements sociaux précoce et adulte déterminent les patrons de sénescence actuarielle spécifiques aux sexes chez une espèce à reproduction coopérative La socialité détermine les traits d’histoire de vie par des modifications de l’allocation des ressources aux traits liés à la valeur sélective. Cependant, l’influence des facteurs sociaux à différentes étapes du cycle de vie sur la sénescence reste encore largement méconnue. Afin de répondre à cette question, nous avons mesuré l’influence de l’environnement social précoce et adulte sur la sénescence actuarielle chez la marmotte alpine, une espèce pratiquant l’élevage coopératif. L’influence d’auxiliaires sur la sénescence actuarielle diffère très fortement selon le moment du cycle de vie où l’aide est apportée et selon le sexe du dominant. Recevoir de l’aide durant la vie adulte ralentit la sénescence dans les deux sexes. Cependant, l’effet de la présence d’auxiliaires à la naissance du dominant diffère entre sexes. Parmi les dominants qui ont reçu de l’aide durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus lentement alors que les mâles vieillissent plus vite. Parmi les dominants qui n’ont pas bénéficié d’auxiliaires durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus vite. L’environnement social détermine donc la sénescence, mais les effets diffèrent selon le sexe et les étapes de vie. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699513 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699513">Read the Article</a></i> </p> --><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>ndividuals from social species typically show a slow growth, a delayed age at first reproduction, and a long life compared to individuals from non-social species with similar size. In cooperative breeders such as meerkats, wolves, or beavers, helpers assist a dominant pair to raise pups. So far, whether sociality influences actuarial senescence (i.e. the age-specific decrease in survival) remains unknown, although helpers take care of pups, which contributes to decreasing the amount of energy that dominants allocate to parental care. We can thus expect that the presence of helpers delays and slows down senescence.</p> <p>A team of researchers from the University of Lyon combined their expertise in demography and sociality to test this expectation in a cooperative breeder, the Alpine marmot. They found that the beneficial effect of helpers depended on the timing of the help. Having helpers as adult slowed down much senescence more than having helpers early in life. Moreover, the benefits of being helped was sex-specific, with actuarial senescence reduced in females but not in males.</p> <p>Their work emphasizes that sociality influences senescence but that the benefits in terms of reduced senescence are sex-specific and depend on when help occurs. These findings have important theoretical implications on current evolutionary theories of ageing, which do not include yet a social component. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>ociality modulates life history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided, and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex-specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among dominants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence, but acts differently between sexes and life stages. </p> <h4>Résumé : Les environnements sociaux précoce et adulte déterminent les patrons de sénescence actuarielle spécifiques aux sexes chez une espèce à reproduction coopérative</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>a socialité détermine les traits d’histoire de vie par des modifications de l’allocation des ressources aux traits liés à la valeur sélective. Cependant, l’influence des facteurs sociaux à différentes étapes du cycle de vie sur la sénescence reste encore largement méconnue. Afin de répondre à cette question, nous avons mesuré l’influence de l’environnement social précoce et adulte sur la sénescence actuarielle chez la marmotte alpine, une espèce pratiquant l’élevage coopératif. L’influence d’auxiliaires sur la sénescence actuarielle diffère très fortement selon le moment du cycle de vie où l’aide est apportée et selon le sexe du dominant. Recevoir de l’aide durant la vie adulte ralentit la sénescence dans les deux sexes. Cependant, l’effet de la présence d’auxiliaires à la naissance du dominant diffère entre sexes. Parmi les dominants qui ont reçu de l’aide durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus lentement alors que les mâles vieillissent plus vite. Parmi les dominants qui n’ont pas bénéficié d’auxiliaires durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus vite. L’environnement social détermine donc la sénescence, mais les effets diffèrent selon le sexe et les étapes de vie. </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, 25 Jul 2018 05:00:00 GMT “The biogeographical patterns of species richness and abundance distribution in stream diatoms are driven by climate and water chemistry” https://amnat.org/an/newpapers/NovPassy.html The DOI will be https://dx.doi.org/10.1086/699830 Stream diatom richness and abundance distribution at subcontinental scales are driven by climate and water chemistry The declines in biodiversity at higher latitudes and elevations are among the oldest studied, yet still not fully explained ecological patterns. Related to biodiversity is the balance between common and rare species, reflected in the shape of the species abundance distribution (SAD). Higher biodiversity is linked to greater community functionality and improved services to humans, such as increased water quality. The degree of species commonness and rarity has implications for ecosystem functions and conservation. While there are many, predominantly climate-based theories and hypotheses about the spatial variability in biodiversity, little is known about the patterns and causes of variability in the SAD. To address this deficiency, an international team of scientists, led by Dr. Sophia Passy from the University of Texas at Arlington, has explored the biodiversity and SAD of diatoms, an important group of producers in stream ecosystems. They demonstrated that in both the US and Finland, diatom richness and the SAD exhibited distinct spatial patterns (i.e., primarily longitudinal in the US, but latitudinal in Finland), deviating from prior observations and thus inconsistent with existing climate-based concepts. These patterns were instead described with climate-water chemistry models, showing that more diverse communities with a more even distribution of common and rare species occur in streams of higher temperature seasonality and total phosphorus levels. Given that temperature seasonality is projected to decrease with global warming because the cold months are becoming warmer, diatom biodiversity and abundance equality may decline and lead to diminished community services. The operation of both climate and water chemistry mechanisms in structuring diatom communities underscores their complex response to the environment and the necessity for novel predictive frameworks. Abstract In this inter-continental study of stream diatoms, we asked three important but still unresolved ecological questions: 1) What factors drive the biogeography of species richness and species abundance distribution (SAD); 2) Are climate-related hypotheses, which have dominated the research on the latitudinal and altitudinal diversity gradients, adequate in explaining spatial biotic variability; and 3) Is the SAD response to the environment independent of richness? We tested a number of climatic theories and hypotheses (i.e., the species-energy theory, the metabolic theory, the energy variability hypothesis, and the climatic tolerance hypothesis) but found no support for any of these concepts as the relationships of richness with explanatory variables were non-existent, weak or unexpected. Instead, we demonstrated that diatom richness and SAD evenness generally increased with temperature seasonality and at mid- to high total phosphorus concentrations. The spatial patterns of diatom richness and the SAD—mainly longitudinal in the US, but latitudinal in Finland—were defined primarily by the covariance of climate and water chemistry with space. The SAD was not entirely controlled by richness, emphasizing its utility for ecological research. Thus, we found support for the operation of both climate and water chemistry mechanisms in structuring diatom communities, which underscores their complex response to the environment and the necessity for novel predictive frameworks. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699830 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699830">Read the Article</a></i> </p> --> <p><b>Stream diatom richness and abundance distribution at subcontinental scales are driven by climate and water chemistry </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he declines in biodiversity at higher latitudes and elevations are among the oldest studied, yet still not fully explained ecological patterns. Related to biodiversity is the balance between common and rare species, reflected in the shape of the species abundance distribution (SAD). Higher biodiversity is linked to greater community functionality and improved services to humans, such as increased water quality. The degree of species commonness and rarity has implications for ecosystem functions and conservation. While there are many, predominantly climate-based theories and hypotheses about the spatial variability in biodiversity, little is known about the patterns and causes of variability in the SAD. To address this deficiency, an international team of scientists, led by Dr. Sophia Passy from the University of Texas at Arlington, has explored the biodiversity and SAD of diatoms, an important group of producers in stream ecosystems. They demonstrated that in both the US and Finland, diatom richness and the SAD exhibited distinct spatial patterns (i.e., primarily longitudinal in the US, but latitudinal in Finland), deviating from prior observations and thus inconsistent with existing climate-based concepts. These patterns were instead described with climate-water chemistry models, showing that more diverse communities with a more even distribution of common and rare species occur in streams of higher temperature seasonality and total phosphorus levels. Given that temperature seasonality is projected to decrease with global warming because the cold months are becoming warmer, diatom biodiversity and abundance equality may decline and lead to diminished community services. The operation of both climate and water chemistry mechanisms in structuring diatom communities underscores their complex response to the environment and the necessity for novel predictive frameworks. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n this inter-continental study of stream diatoms, we asked three important but still unresolved ecological questions: 1) What factors drive the biogeography of species richness and species abundance distribution (SAD); 2) Are climate-related hypotheses, which have dominated the research on the latitudinal and altitudinal diversity gradients, adequate in explaining spatial biotic variability; and 3) Is the SAD response to the environment independent of richness? We tested a number of climatic theories and hypotheses (i.e., the species-energy theory, the metabolic theory, the energy variability hypothesis, and the climatic tolerance hypothesis) but found no support for any of these concepts as the relationships of richness with explanatory variables were non-existent, weak or unexpected. Instead, we demonstrated that diatom richness and SAD evenness generally increased with temperature seasonality and at mid- to high total phosphorus concentrations. The spatial patterns of diatom richness and the SAD—mainly longitudinal in the US, but latitudinal in Finland—were defined primarily by the covariance of climate and water chemistry with space. The SAD was not entirely controlled by richness, emphasizing its utility for ecological research. Thus, we found support for the operation of both climate and water chemistry mechanisms in structuring diatom communities, which underscores their complex response to the environment and the necessity for novel predictive frameworks. </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, 25 Jul 2018 05:00:00 GMT “Multi-scale immune selection and the transmission-diversity feedback in antigenically diverse pathogen systems” https://amnat.org/an/newpapers/DecHolding-A.html The DOI will be https://dx.doi.org/10.1086/699535 Mathematical model shows how immune selection balances the transmission-diversity feedback in pathogen systems Abstract Antigenic diversity is commonly used by pathogens to enhance their transmission success. Within-host clonal antigenic variation helps to maintain long infectious periods, whereas high levels of allelic diversity at the population-level significantly expands the pool of susceptible individuals. Diversity, however, is not necessarily a static property of a pathogen population but in many cases generated by the very act of infection and transmission, and it is therefore expected to respond dynamically to changes in transmission and immune selection. We hypothesised that this coupling creates a positive feedback whereby infection and disease transmission promote the generation of diversity, which itself facilitates immune evasion and further infections. To investigate this link in more detail we considered the human malaria parasite Plasmodium falciparum, one of the most important antigenically diverse pathogens. We developed an individual-based model in which antigenic diversity emerges as a dynamic property from the underlying transmission processes. Our results show that the balance between stochastic extinction and the generation of new antigenic variants is intrinsically linked to within-host and between-host immune selection. This in turn determines the level of diversity that can be maintained in a given population. Furthermore, the transmission-diversity feedback can lead to temporal lags in the response to natural or intervention-induced perturbations in transmission rates. Our results therefore have important implications for monitoring and assessing the effectiveness of disease control efforts. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699535 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699535">Read the Article</a></i> </p> --> <p><b>Mathematical model shows how immune selection balances the transmission-diversity feedback in pathogen systems </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;">A</span>ntigenic diversity is commonly used by pathogens to enhance their transmission success. Within-host clonal antigenic variation helps to maintain long infectious periods, whereas high levels of allelic diversity at the population-level significantly expands the pool of susceptible individuals. Diversity, however, is not necessarily a static property of a pathogen population but in many cases generated by the very act of infection and transmission, and it is therefore expected to respond dynamically to changes in transmission and immune selection. We hypothesised that this coupling creates a positive feedback whereby infection and disease transmission promote the generation of diversity, which itself facilitates immune evasion and further infections. To investigate this link in more detail we considered the human malaria parasite <i>Plasmodium falciparum</i>, one of the most important antigenically diverse pathogens. We developed an individual-based model in which antigenic diversity emerges as a dynamic property from the underlying transmission processes. Our results show that the balance between stochastic extinction and the generation of new antigenic variants is intrinsically linked to within-host and between-host immune selection. This in turn determines the level of diversity that can be maintained in a given population. Furthermore, the transmission-diversity feedback can lead to temporal lags in the response to natural or intervention-induced perturbations in transmission rates. Our results therefore have important implications for monitoring and assessing the effectiveness of disease control efforts. </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, 25 Jul 2018 05:00:00 GMT “Periodic, parasite-mediated selection for and against sex” https://amnat.org/an/newpapers/NovGibson.html The DOI will be https://dx.doi.org/10.1086/699829 Coevolving parasites drive fluctuations in the fitness of asexual reproduction: a long-term field and experimental study Sexual reproduction isn’t an efficient way to make offspring, because males do not give birth. To make the most grandchildren, an individual female should, theoretically, clone herself. Why then is sexual reproduction such a common reproductive strategy? The Red Queen hypothesis suggests that parasites periodically give sexual females an advantage over clonal females. This study supports the Red Queen hypothesis: long-term field and experimental data indicate that parasites drive fluctuations in the fitness and frequency of clones. These long-term field data revealed dramatic variation in the infection rate of asexual females at Lake Alexandrina: in the early 2000s, asexual females were substantially more infected by a sterilizing trematode (Microphallus) than were sexual females. By 2012, asexual females had declined in frequency and become substantially less infected than sexual females. In contrast to the wide variation in asexual infection, the infection rate of sexual females remained steady over the years.The researchers predicted that these rare asexual females should begin to increase in frequency, because (1) asexuals can make more grand-offspring than sexuals and (2) they were less infected than the sexuals. If asexual females did not increase in frequency, the authors would reject the Red Queen hypothesis, because some force other than parasites must be preventing asexuals from outcompeting sexuals. In support of the prediction, asexual females nearly tripled in frequency at Lake Alexandrina from 2012 to 2016. The researchers ran a parallel experiment in freshwater tanks, where they allowed sexual and asexual snails from Lake Alexandrina to compete with one another in a simplified environment that isolated the effect of parasites. Asexual females also increased in frequency in these tanks. The fact that the researchers saw similar results in the field and the tanks argues that parasites contributed to the changes in asexual frequency in the field. These results show periodic selection both for and against sex. The study demonstrates the need for long-term field data in studying host-parasite coevolution and the Red Queen. Single snapshots in time would present a misleading, simplified picture of parasite-mediated selection on reproductive mode. In keeping with this lesson, the researchers continue to follow the ongoings at Lake Alexandrina – they predict that the local parasites will begin to heavily infect asexuals again as asexual females increase in frequency. Abstract Asexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per-capita birth rate advantage of asexuals. Under the Red Queen, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail Potamopyrgus antipodarum and its coevolving parasite Microphallus sp. In the early 2000s, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals, but varied far more. This variation in asexual infection prevalence suggests the potential for parasite-mediated fluctuations in asexual fitness. Accordingly, we detected fitness consequences of the shift in parasite selection: when they were less infected than sexuals, asexuals increased in frequency in the field and in paired mesocosms that isolated the effect of parasites. The match between field and experiment argues that coevolving parasites drive temporal change in the relative fitness and frequency of asexuals, potentially promoting the coexistence of reproductive modes in P.&nbsp;antipodarum. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699829 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699829">Read the Article</a></i> </p> --> <p><b>Coevolving parasites drive fluctuations in the fitness of asexual reproduction: a long-term field and experimental study </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>exual reproduction isn’t an efficient way to make offspring, because males do not give birth. To make the most grandchildren, an individual female should, theoretically, clone herself. Why then is sexual reproduction such a common reproductive strategy? The Red Queen hypothesis suggests that parasites periodically give sexual females an advantage over clonal females. This study supports the Red Queen hypothesis: long-term field and experimental data indicate that parasites drive fluctuations in the fitness and frequency of clones. </p><p>These long-term field data revealed dramatic variation in the infection rate of asexual females at Lake Alexandrina: in the early 2000s, asexual females were substantially more infected by a sterilizing trematode (<I>Microphallus</I>) than were sexual females. By 2012, asexual females had declined in frequency and become substantially less infected than sexual females. In contrast to the wide variation in asexual infection, the infection rate of sexual females remained steady over the years.</p><p>The researchers predicted that these rare asexual females should begin to increase in frequency, because (1) asexuals can make more grand-offspring than sexuals and (2) they were less infected than the sexuals. If asexual females did not increase in frequency, the authors would reject the Red Queen hypothesis, because some force other than parasites must be preventing asexuals from outcompeting sexuals. In support of the prediction, asexual females nearly tripled in frequency at Lake Alexandrina from 2012 to 2016. The researchers ran a parallel experiment in freshwater tanks, where they allowed sexual and asexual snails from Lake Alexandrina to compete with one another in a simplified environment that isolated the effect of parasites. Asexual females also increased in frequency in these tanks. The fact that the researchers saw similar results in the field and the tanks argues that parasites contributed to the changes in asexual frequency in the field. </p><p>These results show periodic selection both for and against sex. The study demonstrates the need for long-term field data in studying host-parasite coevolution and the Red Queen. Single snapshots in time would present a misleading, simplified picture of parasite-mediated selection on reproductive mode. In keeping with this lesson, the researchers continue to follow the ongoings at Lake Alexandrina – they predict that the local parasites will begin to heavily infect asexuals again as asexual females increase in frequency. </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>sexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per-capita birth rate advantage of asexuals. Under the Red Queen, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail <i>Potamopyrgus antipodarum</i> and its coevolving parasite <i>Microphallus</i> sp. In the early 2000s, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals, but varied far more. This variation in asexual infection prevalence suggests the potential for parasite-mediated fluctuations in asexual fitness. Accordingly, we detected fitness consequences of the shift in parasite selection: when they were less infected than sexuals, asexuals increased in frequency in the field and in paired mesocosms that isolated the effect of parasites. The match between field and experiment argues that coevolving parasites drive temporal change in the relative fitness and frequency of asexuals, potentially promoting the coexistence of reproductive modes in <i>P.&nbsp;antipodarum</i>. </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, 25 Jul 2018 05:00:00 GMT “Early-life stress strengthens trait covariance: a plastic response that results in reduced flexibility” https://amnat.org/an/newpapers/NovMerrill.html The DOI will be https://dx.doi.org/10.1086/699839 Early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications Nobody likes stress; it can result in suppressed immunity, increased levels of free radicals, and elevated energy expenditure, among others. But for most organisms, once the stressor has passed, things revert to normal. For developing organisms, however, stressful experiences can have permanent effects. Individuals stressed in early life may be smaller, have less impressive sexual displays, develop altered stress responses later in life, and have modified immune function. In addition to impacting the development of these individual traits, early-life stress could also alter the relationships among different traits, or within traits over time by more broadly impacting an organism’s developmental machinery. Merrill and Grindstaff investigated this idea and found that zebra finches exposed to simulated early-life stress in the form of daily oral doses of the “stress hormone” corticosterone, developed along more rigid trajectories.As metrics of developmental flexibility, Merrill and Grindstaff measured morphological and physiological traits in control and corticosterone-treated birds prior to, during, and after corticosterone administration, which occurred during the nestling and fledgling stages. They then examined the strength of association within traits over time (e.g. body mass when the birds were 10 and 60 days old) and among different traits at the same age (e.g. body mass and wing length when the birds were 60 days old) to determine whether early-life stress resulted in tighter or weaker trait correlations. All of the within-trait correlations, and the vast majority of the among-trait correlations, were tighter for corticosterone-treated birds, providing strong evidence that sustained exposure to elevated levels of this stress hormone in early-life broadly alters developmental patterns. This is important because independent of early-life treatment, birds with tighter within and among trait correlations died earlier. If developmental flexibility is constrained by early-life stress, then this alteration may have profound impacts on the organism and could limit capacity to respond to changing environmental conditions. Abstract Stress exposure during development can impact both the expression of individual traits and associations between traits, but whether stress results in stronger or weaker associations between traits is unclear. In this study, we examined within and among-trait associations for morphological and physiological traits in zebra finches (Taeniopygia guttata) exposed to corticosterone (CORT) during the nestling and fledgling stages, and in control birds. Birds exposed to CORT exhibited stronger within-trait correlations over time and stronger associations among traits. We found preliminary evidence that birds that died before the median age of death had stronger within and among-trait correlations independent of treatment, and among CORT-treated birds, smaller birds were more likely to survive beyond the median age than larger birds. These findings suggest that early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications, and that these costs may be greater for larger offspring. Furthermore, our results provide experimental evidence for pleiotropic effects of hormones during development through altered patterns of phenotypic correlation. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699839 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699839">Read the Article</a></i> </p> --> <p><b>Early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications </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;">N</span>obody likes stress; it can result in suppressed immunity, increased levels of free radicals, and elevated energy expenditure, among others. But for most organisms, once the stressor has passed, things revert to normal. For developing organisms, however, stressful experiences can have permanent effects. Individuals stressed in early life may be smaller, have less impressive sexual displays, develop altered stress responses later in life, and have modified immune function. In addition to impacting the development of these individual traits, early-life stress could also alter the relationships among different traits, or within traits over time by more broadly impacting an organism’s developmental machinery. Merrill and Grindstaff investigated this idea and found that zebra finches exposed to simulated early-life stress in the form of daily oral doses of the “stress hormone” corticosterone, developed along more rigid trajectories.</p><p>As metrics of developmental flexibility, Merrill and Grindstaff measured morphological and physiological traits in control and corticosterone-treated birds prior to, during, and after corticosterone administration, which occurred during the nestling and fledgling stages. They then examined the strength of association within traits over time (e.g. body mass when the birds were 10 and 60 days old) and among different traits at the same age (e.g. body mass and wing length when the birds were 60 days old) to determine whether early-life stress resulted in tighter or weaker trait correlations. All of the within-trait correlations, and the vast majority of the among-trait correlations, were tighter for corticosterone-treated birds, providing strong evidence that sustained exposure to elevated levels of this stress hormone in early-life broadly alters developmental patterns. This is important because independent of early-life treatment, birds with tighter within and among trait correlations died earlier. If developmental flexibility is constrained by early-life stress, then this alteration may have profound impacts on the organism and could limit capacity to respond to changing environmental 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;">S</span>tress exposure during development can impact both the expression of individual traits and associations between traits, but whether stress results in stronger or weaker associations between traits is unclear. In this study, we examined within and among-trait associations for morphological and physiological traits in zebra finches (<i>Taeniopygia guttata</i>) exposed to corticosterone (CORT) during the nestling and fledgling stages, and in control birds. Birds exposed to CORT exhibited stronger within-trait correlations over time and stronger associations among traits. We found preliminary evidence that birds that died before the median age of death had stronger within and among-trait correlations independent of treatment, and among CORT-treated birds, smaller birds were more likely to survive beyond the median age than larger birds. These findings suggest that early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications, and that these costs may be greater for larger offspring. Furthermore, our results provide experimental evidence for pleiotropic effects of hormones during development through altered patterns of phenotypic correlation. </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, 24 Jul 2018 05:00:00 GMT “A new framework for evaluating estimates of symbiotic nitrogen fixation in forests” https://amnat.org/an/newpapers/NovWinbourne-A.html The DOI will be https://dx.doi.org/10.1086/699828 Rates of symbiotic nitrogen fixation are more uncertain than previously believed, shown with field data and simulations Abstract Symbiotic nitrogen fixation (SNF) makes atmospheric nitrogen biologically available and regulates carbon storage in many terrestrial ecosystems. Despite its global importance, estimates of SNF rates are highly uncertain, particularly in tropical forests where rates are assumed to be high. Here we provide a framework for evaluating the uncertainty of sample-based SNF estimates and discuss its implications for quantifying SNF and thus understanding of forest function. We apply this framework to field datasets from six lowland tropical rainforests (mature and secondary) in Brazil and Costa Rica. We use this dataset to estimate parameters influencing SNF estimation error, notably the root nodule abundance and variation in SNF rates among soil cores containing root nodules. We then use simulations to gauge the relationship between sampling effort and SNF estimation accuracy for a combination of parameters. Field data illuminate a highly right skewed log-normal distribution of SNF rates among soil cores containing root nodules which were rare and spanned five orders of magnitude. Consequently, simulations demonstrated that sample sizes of hundreds to even thousands of soil cores are needed to obtain estimates of SNF that are within, for example, a factor of 2 of the actual rate with 75% probability. This represents sample sizes that are larger than most studies to date. As a result of this previously undescribed uncertainty, we suggest current estimates of SNF in tropical forests are not sufficiently constrained to elucidate forest stand-level controls of SNF, which hinders our understanding of the impact of SNF on tropical forest ecosystem processes. Uma nova abordagem para avaliar as estimativas de fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio em florestas A&nbsp;fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio (FSN) torna o nitrog&ecirc;nio atmosf&eacute;rico biologicamente dispon&iacute;vel e regula o armazenamento de carbono em muitos ecossistemas terrestres. Apesar da sua import&acirc;ncia global, as estimativas de taxas de FSN ainda s&atilde;o muito incertas, principalmente em florestas tropicais, onde presume-se que as taxas sejam altas. O presente estudo avalia as incertezas nas estimativas de FSN baseadas em coleta de amostras e discute as implica&ccedil;&otilde;es desses resultados na quantifica&ccedil;&atilde;o de FSN, com intuito de melhorar o entendimento sobre o funcionamento das florestas tropicais. Esse esquema de avalia&ccedil;&atilde;o de incerteza foi aplicado a um conjunto de dados oriundos de seis florestas tropicais de terras baixas (maduras e secund&aacute;rias) localizadas no Brasil e na Costa Rica. Usamos esse conjunto de dados para estimar os par&acirc;metros que influenciam o erro da estimativa de FSN, principalmente a abund&acirc;ncia de n&oacute;dulos radiculares e varia&ccedil;&atilde;o nas taxas de FSN. Em seguida, calculamos atrav&eacute;s de simula&ccedil;&otilde;es a rela&ccedil;&atilde;o entre o esfor&ccedil;o de amostragem e a precis&atilde;o da estimativa de FSN. Os dados de campo evidenciam uma distribui&ccedil;&atilde;o log-normal com alta assimetria &agrave; direita das taxas de FSN nas amostras de solo contendo n&oacute;dulos de raiz, os quais foram raros. Consequentemente, as simula&ccedil;&otilde;es demonstraram que s&atilde;o necess&aacute;rias centenas ou at&eacute; mesmo milhares de amostras para se obter estimativas de FSN que tenham, por exemplo, 75% de probabilidade de distar da taxa verdadeira 2 vezes ou menos. Esse n&uacute;mero &eacute; muito maior do que o usado na maioria dos estudos j&aacute; publicados. Sugerimos que estimativas atuais de FSN em florestas tropicais s&atilde;o muito incertas para elucidar os controles de FSN em n&iacute;vel de parcelas amostrais, dificultando nossa compreens&atilde;o do impacto da FSN nos processos ecossist&ecirc;micos das florestas tropicais. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699828 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699828">Read the Article</a></i> </p> --> <p><b>Rates of symbiotic nitrogen fixation are more uncertain than previously believed, shown with field data and simulations </b></p><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">S</span>ymbiotic nitrogen fixation (SNF) makes atmospheric nitrogen biologically available and regulates carbon storage in many terrestrial ecosystems. Despite its global importance, estimates of SNF rates are highly uncertain, particularly in tropical forests where rates are assumed to be high. Here we provide a framework for evaluating the uncertainty of sample-based SNF estimates and discuss its implications for quantifying SNF and thus understanding of forest function. We apply this framework to field datasets from six lowland tropical rainforests (mature and secondary) in Brazil and Costa Rica. We use this dataset to estimate parameters influencing SNF estimation error, notably the root nodule abundance and variation in SNF rates among soil cores containing root nodules. We then use simulations to gauge the relationship between sampling effort and SNF estimation accuracy for a combination of parameters. Field data illuminate a highly right skewed log-normal distribution of SNF rates among soil cores containing root nodules which were rare and spanned five orders of magnitude. Consequently, simulations demonstrated that sample sizes of hundreds to even thousands of soil cores are needed to obtain estimates of SNF that are within, for example, a factor of 2 of the actual rate with 75% probability. This represents sample sizes that are larger than most studies to date. As a result of this previously undescribed uncertainty, we suggest current estimates of SNF in tropical forests are not sufficiently constrained to elucidate forest stand-level controls of SNF, which hinders our understanding of the impact of SNF on tropical forest ecosystem processes.</p> <h4>Uma nova abordagem para avaliar as estimativas de fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio em florestas</h4> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">A</span>&nbsp;fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio (FSN) torna o nitrog&ecirc;nio atmosf&eacute;rico biologicamente dispon&iacute;vel e regula o armazenamento de carbono em muitos ecossistemas terrestres. Apesar da sua import&acirc;ncia global, as estimativas de taxas de FSN ainda s&atilde;o muito incertas, principalmente em florestas tropicais, onde presume-se que as taxas sejam altas. O presente estudo avalia as incertezas nas estimativas de FSN baseadas em coleta de amostras e discute as implica&ccedil;&otilde;es desses resultados na quantifica&ccedil;&atilde;o de FSN, com intuito de melhorar o entendimento sobre o funcionamento das florestas tropicais. Esse esquema de avalia&ccedil;&atilde;o de incerteza foi aplicado a um conjunto de dados oriundos de seis florestas tropicais de terras baixas (maduras e secund&aacute;rias) localizadas no Brasil e na Costa Rica. Usamos esse conjunto de dados para estimar os par&acirc;metros que influenciam o erro da estimativa de FSN, principalmente a abund&acirc;ncia de n&oacute;dulos radiculares e varia&ccedil;&atilde;o nas taxas de FSN. Em seguida, calculamos atrav&eacute;s de simula&ccedil;&otilde;es a rela&ccedil;&atilde;o entre o esfor&ccedil;o de amostragem e a precis&atilde;o da estimativa de FSN. Os dados de campo evidenciam uma distribui&ccedil;&atilde;o log-normal com alta assimetria &agrave; direita das taxas de FSN nas amostras de solo contendo n&oacute;dulos de raiz, os quais foram raros. Consequentemente, as simula&ccedil;&otilde;es demonstraram que s&atilde;o necess&aacute;rias centenas ou at&eacute; mesmo milhares de amostras para se obter estimativas de FSN que tenham, por exemplo, 75% de probabilidade de distar da taxa verdadeira 2 vezes ou menos. Esse n&uacute;mero &eacute; muito maior do que o usado na maioria dos estudos j&aacute; publicados. Sugerimos que estimativas atuais de FSN em florestas tropicais s&atilde;o muito incertas para elucidar os controles de FSN em n&iacute;vel de parcelas amostrais, dificultando nossa compreens&atilde;o do impacto da FSN nos processos ecossist&ecirc;micos das florestas tropicais.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 24 Jul 2018 05:00:00 GMT “Female-biased sex ratios increase colony survival and reproductive output in the spider Anelosimus studiosus” https://amnat.org/an/newpapers/NovLichtenstein.html The DOI will be https://dx.doi.org/10.1086/699838 Female-biased sex ratios increase social spider colony survival, generating group selection on female-biased sex ratios Animals across the world tend to have 1&thinsp;:&thinsp;1 sex ratios, because whichever sex is rarer, it will always be advantageous to produce more of it. However, a few animals have highly female-skewed ratios, including social spiders, inbred spiders that work together to capture prey. In a new paper appearing in The&nbsp;American Naturalist, James L. L. Lichtenstein and colleagues evaluate one advantage to producing many daughters: Extremely inbred social groups with many females can grow more quickly, helping groups survive and reproduce. The authors tested this by assembling colonies of the semi-social spider Anelosimus studiosus and then putting colonies in the wild with manipulated sizes and sex ratios in areas where spider colonies thrive and places where they struggle. The researchers thought that groups with female-biased sex ratios would be more likely to survive and produce egg cases, especially for small colonies and colonies in areas where spiders struggle to survive. After five months, the scientists returned to these colonies to see whether they were alive and how many egg cases they produced. As expected, female-biased colonies were more likely to survive and produced more egg cases. These advantages were stronger when spider colonies were small and were in tough areas. This means that colonies full of female spiders were able to flourish in harrowing conditions by doing more helping capture prey and maintain webs more than male spiders, producing offspring who can work, or both. This advantage may explain the evolution of female-biased ratios in this very interesting yet very specific case. Abstract Negative frequency-dependent selection acting on the sexes is hypothesized to drive populations towards a balanced sex ratio. However, numerous examples of female-biased sex ratios pepper the arthropods. Theoretical examinations have proposed that female-biased populations or groups can have higher chances of surviving and propagating, which may be advantageous. We evaluate this hypothesis in the semi-social spider, Anelosimus studiosus, by creating artificial colonies of varying sex ratios and sizes and observing colony performance at sites with high vs. low group extinction rates. We also tested whether colony extinction rates and sex ratios were correlated across 25 collection sites spanning 10º latitude. We found that colonies with female-biased sex ratios produced more egg cases and were more likely to survive the duration of a field season, suggesting that female-biased sex ratios confer both survival and reproductive advantages upon colonies. The effect of sex ratio on colony survival and reproductive output was strongest for small colonies in high extinction areas. Moreover, we found that female-biased sex ratios correlated with greater extinction rates across 25 sites, indicating that female-biased sex ratios may have evolved at some sites in response to high extinction rates. These findings suggest that selection favoring groups with female-biased sex ratios may operate in A.&nbsp;studiosus, shedding light on some of factors that may drive the evolution of biased sex ratios. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699838 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699838">Read the Article</a></i> </p> --> <p><b>Female-biased sex ratios increase social spider colony survival, generating group selection on female-biased sex ratios </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>nimals across the world tend to have 1&thinsp;:&thinsp;1 sex ratios, because whichever sex is rarer, it will always be advantageous to produce more of it. However, a few animals have highly female-skewed ratios, including social spiders, inbred spiders that work together to capture prey. In a new paper appearing in <i>The&nbsp;American Naturalist</i>, James L. L. Lichtenstein and colleagues evaluate one advantage to producing many daughters: Extremely inbred social groups with many females can grow more quickly, helping groups survive and reproduce. The authors tested this by assembling colonies of the semi-social spider <i>Anelosimus studiosus</i> and then putting colonies in the wild with manipulated sizes and sex ratios in areas where spider colonies thrive and places where they struggle. The researchers thought that groups with female-biased sex ratios would be more likely to survive and produce egg cases, especially for small colonies and colonies in areas where spiders struggle to survive. After five months, the scientists returned to these colonies to see whether they were alive and how many egg cases they produced. </p> <p>As expected, female-biased colonies were more likely to survive and produced more egg cases. These advantages were stronger when spider colonies were small and were in tough areas. This means that colonies full of female spiders were able to flourish in harrowing conditions by doing more helping capture prey and maintain webs more than male spiders, producing offspring who can work, or both. This advantage may explain the evolution of female-biased ratios in this very interesting yet very specific case.</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;">N</span>egative frequency-dependent selection acting on the sexes is hypothesized to drive populations towards a balanced sex ratio. However, numerous examples of female-biased sex ratios pepper the arthropods. Theoretical examinations have proposed that female-biased populations or groups can have higher chances of surviving and propagating, which may be advantageous. We evaluate this hypothesis in the semi-social spider, <i>Anelosimus studiosus</i>, by creating artificial colonies of varying sex ratios and sizes and observing colony performance at sites with high vs. low group extinction rates. We also tested whether colony extinction rates and sex ratios were correlated across 25 collection sites spanning 10º latitude. We found that colonies with female-biased sex ratios produced more egg cases and were more likely to survive the duration of a field season, suggesting that female-biased sex ratios confer both survival and reproductive advantages upon colonies. The effect of sex ratio on colony survival and reproductive output was strongest for small colonies in high extinction areas. Moreover, we found that female-biased sex ratios correlated with greater extinction rates across 25 sites, indicating that female-biased sex ratios may have evolved at some sites in response to high extinction rates. These findings suggest that selection favoring groups with female-biased sex ratios may operate in <i>A.&nbsp;studiosus</i>, shedding light on some of factors that may drive the evolution of biased sex ratios.</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, 24 Jul 2018 05:00:00 GMT “Dividing a maternal pie among half-sibs: genetic conflicts and the control of resource allocation to seeds in maize” https://amnat.org/an/newpapers/NovCailleau.html The DOI will be https://dx.doi.org/10.1086/699653 Sibling rivalry for maternal resource allocation: it also occurs in plants! Offspring size is a key fitness trait, which often results from various, possibly conflictual, interactions among parents and offspring. In angiosperms, seed mass is most often thought to result from maternal control. Paternal genotype and sibling rivalry is thought to play little role in this resource allocation. In this paper, Cailleau et al. present both a large-scale experiment and a new method to partition how the maternal sporophyte and half-sibs with different paternal genomes influence resource allocation. They find that the paternal genotypes in seeds influenced resource allocation by interacting with both the maternal plant and half-sibs. This paternal genotype influences the resource allocated to seed, often eliciting a greater maternal allocation than that observed upon selfing. They also find that there is strong sibling rivalry: maternal resources are allocated entirely competitively, and seeds with different paternal genotypes show different competitive ability to take up this resource. Furthermore, the researchers find evidence that competition between seeds with different paternal genotypes entails a cost and reduces the overall amount of resources allocated to the ear. These findings provide a better view of the control of resource allocation to seeds, which is essential for conflict theories, and may prove useful to optimize yield. Abstract Resource allocation to offspring is the battleground for various intra-familial conflicts. Understanding these conflicts requires knowledge of how the different actors (mother, siblings with different paternal genotypes) influence resource allocation. In angiosperms, resource to seeds is allocated post-fertilization and the paternally inherited genome in offspring can therefore influence resource allocation. However, the precise mode of resource allocation, and in particular the occurrence of sibling rivalry, has been rarely investigated in plants. In this paper, we develop a new method to analyze the resource allocation traits of the different actors (maternal sporophyte and half-sibs) using the data obtained from a large-scale diallel cross experiment in maize involving mixed hand pollination and colors markers to assess seed weight of known paternity. We found strong evidence for the occurrence of sibling rivalry: resources invested in an ear were allocated competitively and offspring with different paternal genotypes aggressively competed for this resource, entailing a measurable direct cost to the mother. We also show how resource allocation can be described for each genotype by two maternal (source effect, average sink responsiveness) and two offspring traits (ability to attract maternal resource, competitive ability towards siblings). We will discuss how these findings help understanding how genetic conflicts shape resource allocation traits in angiosperms. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699653 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699653">Read the Article</a></i> </p> --> <p><b>Sibling rivalry for maternal resource allocation: it also occurs in plants! </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">O</span>ffspring size is a key fitness trait, which often results from various, possibly conflictual, interactions among parents and offspring. In angiosperms, seed mass is most often thought to result from maternal control. Paternal genotype and sibling rivalry is thought to play little role in this resource allocation. In this paper, Cailleau et al. present both a large-scale experiment and a new method to partition how the maternal sporophyte and half-sibs with different paternal genomes influence resource allocation. They find that the paternal genotypes in seeds influenced resource allocation by interacting with both the maternal plant and half-sibs. This paternal genotype influences the resource allocated to seed, often eliciting a greater maternal allocation than that observed upon selfing. They also find that there is strong sibling rivalry: maternal resources are allocated entirely competitively, and seeds with different paternal genotypes show different competitive ability to take up this resource. Furthermore, the researchers find evidence that competition between seeds with different paternal genotypes entails a cost and reduces the overall amount of resources allocated to the ear. These findings provide a better view of the control of resource allocation to seeds, which is essential for conflict theories, and may prove useful to optimize yield. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">R</span>esource allocation to offspring is the battleground for various intra-familial conflicts. Understanding these conflicts requires knowledge of how the different actors (mother, siblings with different paternal genotypes) influence resource allocation. In angiosperms, resource to seeds is allocated post-fertilization and the paternally inherited genome in offspring can therefore influence resource allocation. However, the precise mode of resource allocation, and in particular the occurrence of sibling rivalry, has been rarely investigated in plants. In this paper, we develop a new method to analyze the resource allocation traits of the different actors (maternal sporophyte and half-sibs) using the data obtained from a large-scale diallel cross experiment in maize involving mixed hand pollination and colors markers to assess seed weight of known paternity. We found strong evidence for the occurrence of sibling rivalry: resources invested in an ear were allocated competitively and offspring with different paternal genotypes aggressively competed for this resource, entailing a measurable direct cost to the mother. We also show how resource allocation can be described for each genotype by two maternal (source effect, average sink responsiveness) and two offspring traits (ability to attract maternal resource, competitive ability towards siblings). We will discuss how these findings help understanding how genetic conflicts shape resource allocation traits in angiosperms. </p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 10 Jul 2018 05:00:00 GMT “Disentangling pre- and post-natal maternal age effects on offspring performance in an insect with elaborate maternal care” https://amnat.org/an/newpapers/NovIvimeyC-A.html The DOI will be https://dx.doi.org/10.1086/699654 Abstract Maternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and post-natal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of burying beetle, Nicrophorus vespilloides, to examine both the effects of female pre- and post-natal maternal age on offspring life history traits and the post-care outcomes of mothers while accounting for selective disappearance of post-natal caregivers. Neither pre- nor post-natal maternal age affected offspring longevity or larval weight at hatching, and post-natal age had no effect upon post-care maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg-producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699654 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699654">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;">M</span>aternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and post-natal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of burying beetle, <i>Nicrophorus vespilloides</i>, to examine both the effects of female pre- and post-natal maternal age on offspring life history traits and the post-care outcomes of mothers while accounting for selective disappearance of post-natal caregivers. Neither pre- nor post-natal maternal age affected offspring longevity or larval weight at hatching, and post-natal age had no effect upon post-care maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg-producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care. </p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 10 Jul 2018 05:00:00 GMT “Rising temperatures, molting phenology and epizootic shell disease in the American lobster” https://amnat.org/an/newpapers/NovGroner.html Read the Article Rising temperatures cause phenological mismatch between molting and epizootic shell disease in the American lobster Changing environmental conditions can alter the timing of key events during a species’ lifetime. In some cases this can cause a mismatch between an event and critical environmental or biological conditions. This ‘phenological mismatch’ has been investigated in a variety of scenarios such as the timing of breeding and migration with food availability and predation risk. However, it has not been well examined in the context of disease risk. In this paper, the authors’ investigated how changing seawater temperature is altering responses to an emerging disease of the American lobster, epizootic shell disease (ESD). Using a 34-year mark-recapture dataset from Long Island Sound, CT, the authors investigated relationships between seawater temperature, molting phenology, and seasonal variation of epizootic shell disease (ESD). ESD is an emerging disease of lobsters caused by a suite of bacteria on the lobster cuticle that feed upon materials in the shell. Molting can be beneficial for diseased lobsters because it allows them to discard their diseased shell. The authors’ analyses support the hypothesis that phenological mismatch is linked to seasonal variation in ESD. They found that warmer spring temperatures were associated with earlier spring molting. This increased the length of the intermolt period in the summer, when disease transmission is highest. For juvenile and adult male lobsters, earlier molting was associated with a greater proportion of diseased lobsters in September; however, in October, the proportion of diseased lobsters was most strongly associated with warmer summer seawater temperature. This suggests that spring temperatures affect the timing of the onset of disease by altering molting patterns, but, over time, this signal is swamped by the stronger signal of summer temperatures. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Population impacts of ESD are expected to increase with increasing seawater temperatures. Abstract Phenological mismatch, maladaptive changes in phenology resulting from altered timing of environmental cues, is an increasing concern in many ecological systems, yet its effects on disease are poorly characterized. American lobster (Homarus americanus) is declining at its southern geographic limit. Rising seawater temperatures are associated with seasonal outbreaks of epizootic shell disease (ESD), which peaks in prevalence in the fall. We used a 34-year mark-recapture dataset to investigate relationships between temperature, molting phenology, and ESD in Long Island Sound, where temperatures are increasing at 0.4&thinsp;&deg;C per decade. Our analyses support the hypothesis that phenological mismatch is linked to the epidemiology of ESD. Warming spring temperatures are correlated with earlier spring molting. Lobsters lose diseased cuticle by molting, and early molting increases the intermolt period in the summer, when disease prevalence is increasing to a fall peak. In juvenile and adult male lobsters, September ESD prevalence was correlated with early molting, while October ESD prevalence was correlated with summer seawater temperature. This suggests that temperature-induced molting phenology affects the timing of the onset of ESD, but, later in the summer, this signal is swamped by the stronger signal of summer temperatures, which we hypothesize are associated with an increased rate of new infections. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Yearly survival of diseased lobsters is <50% that of healthy lobsters. Thus, population impacts of ESD are expected to increase with increasing seawater temperatures. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/699478">Read the Article</a></i></p> <p><b>Rising temperatures cause phenological mismatch between molting and epizootic shell disease in the American lobster </b></p><p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">C</span>hanging environmental conditions can alter the timing of key events during a species&rsquo; lifetime. In some cases this can cause a mismatch between an event and critical environmental or biological conditions. This &lsquo;phenological mismatch&rsquo; has been investigated in a variety of scenarios such as the timing of breeding and migration with food availability and predation risk. However, it has not been well examined in the context of disease risk.</p> <p>In this paper, the authors&rsquo; investigated how changing seawater temperature is altering responses to an emerging disease of the American lobster, epizootic shell disease (ESD). Using a 34-year mark-recapture dataset from Long Island Sound, CT, the authors investigated relationships between seawater temperature, molting phenology, and seasonal variation of epizootic shell disease (ESD). ESD is an emerging disease of lobsters caused by a suite of bacteria on the lobster cuticle that feed upon materials in the shell. Molting can be beneficial for diseased lobsters because it allows them to discard their diseased shell.</p> <p>The authors&rsquo; analyses support the hypothesis that phenological mismatch is linked to seasonal variation in ESD. They found that warmer spring temperatures were associated with earlier spring molting. This increased the length of the intermolt period in the summer, when disease transmission is highest. For juvenile and adult male lobsters, earlier molting was associated with a greater proportion of diseased lobsters in September; however, in October, the proportion of diseased lobsters was most strongly associated with warmer summer seawater temperature. This suggests that spring temperatures affect the timing of the onset of disease by altering molting patterns, but, over time, this signal is swamped by the stronger signal of summer temperatures. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Population impacts of ESD are expected to increase with increasing seawater temperatures.</p> <hr /> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">P</span>henological mismatch, maladaptive changes in phenology resulting from altered timing of environmental cues, is an increasing concern in many ecological systems, yet its effects on disease are poorly characterized. American lobster (<i>Homarus americanus</i>) is declining at its southern geographic limit. Rising seawater temperatures are associated with seasonal outbreaks of epizootic shell disease (ESD), which peaks in prevalence in the fall. We used a 34-year mark-recapture dataset to investigate relationships between temperature, molting phenology, and ESD in Long Island Sound, where temperatures are increasing at 0.4&thinsp;&deg;C per decade. Our analyses support the hypothesis that phenological mismatch is linked to the epidemiology of ESD. Warming spring temperatures are correlated with earlier spring molting. Lobsters lose diseased cuticle by molting, and early molting increases the intermolt period in the summer, when disease prevalence is increasing to a fall peak. In juvenile and adult male lobsters, September ESD prevalence was correlated with early molting, while October ESD prevalence was correlated with summer seawater temperature. This suggests that temperature-induced molting phenology affects the timing of the onset of ESD, but, later in the summer, this signal is swamped by the stronger signal of summer temperatures, which we hypothesize are associated with an increased rate of new infections. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Yearly survival of diseased lobsters is &lt;50% that of healthy lobsters. Thus, population impacts of ESD are expected to increase with increasing seawater temperatures.</p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 10 Jul 2018 05:00:00 GMT “Host dispersal responses to resource supplementation determine pathogen spread in wildlife metapopulations” https://amnat.org/an/newpapers/OctBecker.html Read the Article How does resource supplementation and infection affect infectious disease spread in wildlife metapopulations? Urban parks, backyards, landfills, and agricultural fields provide wildlife with access to novel food sources. Food provided by humans in these locations can dramatically alter patterns of animal site fidelity and movement between habitats, with consequences for pathogen spread across the landscape. To better understand how the extent of food-subsidized habitat affects wildlife distributions and infection patterns, researchers at the University of Georgia developed a mathematical model that assumes that animal dispersal and the duration of site occupancy will depend on food availability and abundance at a given site as well as animal infection status. The authors found that both wildlife distributions across the landscape, and pathogen infection prevalence, depend on how productive food-provisioned patches are relative to natural patches. If habitats with human-provided food are occupied for longer by animals and produce more dispersers (such as might occur if animals survive better and produce more offspring when food is abundant and reliable), then infection becomes more widespread as more of the landscape is provisioned. However, if habitats with human-provided food produce fewer dispersers (such as might occur if animals stop moving as much when abundant food is present), then infection prevalence declines as more sites become provisioned. Reducing opportunities for pathogen spread can in turn increase landscape-level occupancy by wildlife. These results highlight that when wildlife are fed by humans, whether at landfills or through recreational wildlife feeding, this can alter the spread of pathogens across a landscape. To determine if food provisioning is beneficial or detrimental for wildlife abundance and health, future work is needed to examine how births, deaths, and movement behavior respond to human-provided resources. These results are especially applicable to highly mobile, nomadic, urban-feeding species such as flying foxes, white ibis (pictured), and many other birds and mammals. The research was led by Daniel Becker, a recent PhD graduate from the University of Georgia, overseen by University of Georgia faculty Sonia Altizer and Richard Hall, and resulted from a summer undergraduate research project from recent UC Berkeley undergraduate Celine Snedden. Abstract Many wildlife species occupy landscapes that vary in the distribution, abundance, and quality of food resources. Increasingly, urbanized and agricultural habitats provide supplemental food resources that can have profound consequences for host distributions, movement patterns, and pathogen exposure. Understanding how host and pathogen dispersal across landscapes is affected by the spatial extent of food-supplemented habitats is therefore important for predicting the consequences for pathogen spread and impacts on host occupancy. Here we develop a generalizable metapopulation model to understand how the relative abundance of provisioned habitats across the landscape, and host dispersal responses to provisioning and infection, influence patch occupancy by hosts and their pathogens. We find that pathogen invasion and landscape-level infection prevalence are greatest when provisioning increases patch attractiveness and disperser production and when infection has minimal costs on dispersal success. Alternatively, if provisioning promotes site fidelity or reduces disperser production, increasing the fraction of food-supplemented habitats can reduce landscape-scale infection prevalence and minimize disease-induced declines in host occupancy. This work highlights the importance of considering how resources and infection jointly influence host dispersal for predicting how changing resource distributions influence the spread of infectious diseases. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/699477">Read the Article</a></i> </p> <p><b>How does resource supplementation and infection affect infectious disease spread in wildlife metapopulations? </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>rban parks, backyards, landfills, and agricultural fields provide wildlife with access to novel food sources. Food provided by humans in these locations can dramatically alter patterns of animal site fidelity and movement between habitats, with consequences for pathogen spread across the landscape. To better understand how the extent of food-subsidized habitat affects wildlife distributions and infection patterns, researchers at the University of Georgia developed a mathematical model that assumes that animal dispersal and the duration of site occupancy will depend on food availability and abundance at a given site as well as animal infection status.</p> <p>The authors found that both wildlife distributions across the landscape, and pathogen infection prevalence, depend on how productive food-provisioned patches are relative to natural patches. If habitats with human-provided food are occupied for longer by animals and produce more dispersers (such as might occur if animals survive better and produce more offspring when food is abundant and reliable), then infection becomes more widespread as more of the landscape is provisioned. However, if habitats with human-provided food produce fewer dispersers (such as might occur if animals stop moving as much when abundant food is present), then infection prevalence declines as more sites become provisioned. Reducing opportunities for pathogen spread can in turn increase landscape-level occupancy by wildlife.</p> <p>These results highlight that when wildlife are fed by humans, whether at landfills or through recreational wildlife feeding, this can alter the spread of pathogens across a landscape. To determine if food provisioning is beneficial or detrimental for wildlife abundance and health, future work is needed to examine how births, deaths, and movement behavior respond to human-provided resources. These results are especially applicable to highly mobile, nomadic, urban-feeding species such as flying foxes, white ibis (pictured), and many other birds and mammals.</p> <p>The research was led by Daniel Becker, a recent PhD graduate from the University of Georgia, overseen by University of Georgia faculty Sonia Altizer and Richard Hall, and resulted from a summer undergraduate research project from recent UC Berkeley undergraduate Celine Snedden.</p> <hr /> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">M</span>any wildlife species occupy landscapes that vary in the distribution, abundance, and quality of food resources. Increasingly, urbanized and agricultural habitats provide supplemental food resources that can have profound consequences for host distributions, movement patterns, and pathogen exposure. Understanding how host and pathogen dispersal across landscapes is affected by the spatial extent of food-supplemented habitats is therefore important for predicting the consequences for pathogen spread and impacts on host occupancy. Here we develop a generalizable metapopulation model to understand how the relative abundance of provisioned habitats across the landscape, and host dispersal responses to provisioning and infection, influence patch occupancy by hosts and their pathogens. We find that pathogen invasion and landscape-level infection prevalence are greatest when provisioning increases patch attractiveness and disperser production and when infection has minimal costs on dispersal success. Alternatively, if provisioning promotes site fidelity or reduces disperser production, increasing the fraction of food-supplemented habitats can reduce landscape-scale infection prevalence and minimize disease-induced declines in host occupancy. This work highlights the importance of considering how resources and infection jointly influence host dispersal for predicting how changing resource distributions influence the spread of infectious diseases.</p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 10 Jul 2018 05:00:00 GMT “Does population structure predict the rate of speciation? A comparative test across Australia's most diverse vertebrate radiation” https://amnat.org/an/newpapers/OctSinghal-A.html Read the Article Abstract Population divergence is the first step in allopatric speciation, as has long been recognized in both theoretical models of speciation and empirical explorations of natural systems. All else being equal, lineages with substantial population differentiation should form new species more quickly than lineages that maintain range-wide genetic cohesion through high levels of gene flow. However, there have been few direct tests of the extent to which population differentiation predicts speciation rates as measured on phylogenetic trees. Here, we explicitly test the links between organismal traits, population-level processes, and phylogenetic speciation rates across a diverse clade of Australian lizards that shows remarkable variation in speciation rate. Using genome-wide ddRAD data from 892 individuals, we generated a comparative dataset on isolation-by-distance and population differentiation across 104 putative species-level lineages (OTUs). We find that species show substantial variation in the extent of population differentiation, and this variation is predicted by organismal traits that are thought to be proxies for dispersal and deme size. However, variation in population structure does not predict variation in speciation rate. Our results suggest that population differentiation is not the rate-limiting step in species formation and that other ecological and historical factors are primary determinants of speciation rates at macroevolutionary scales. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699515"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699515">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;">P</span>opulation divergence is the first step in allopatric speciation, as has long been recognized in both theoretical models of speciation and empirical explorations of natural systems. All else being equal, lineages with substantial population differentiation should form new species more quickly than lineages that maintain range-wide genetic cohesion through high levels of gene flow. However, there have been few direct tests of the extent to which population differentiation predicts speciation rates as measured on phylogenetic trees. Here, we explicitly test the links between organismal traits, population-level processes, and phylogenetic speciation rates across a diverse clade of Australian lizards that shows remarkable variation in speciation rate. Using genome-wide ddRAD data from 892 individuals, we generated a comparative dataset on isolation-by-distance and population differentiation across 104 putative species-level lineages (OTUs). We find that species show substantial variation in the extent of population differentiation, and this variation is predicted by organismal traits that are thought to be proxies for dispersal and deme size. However, variation in population structure does not predict variation in speciation rate. Our results suggest that population differentiation is not the rate-limiting step in species formation and that other ecological and historical factors are primary determinants of speciation rates at macroevolutionary scales. </p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 10 Jul 2018 05:00:00 GMT “The role of geography in adaptive radiation” https://amnat.org/an/newpapers/OctSchenk.html The DOI will be https://dx.doi.org/10.1086/699221 Biogeographic transitions are important drivers of species diversity in adaptive radiations To explain why millions of species exist on Earth, biologists seek to discover how species evolve and the factors promoting diversification. Of particular interest are groups of closely related species that rapidly evolved many new species as they adapted to new niches, a process called adaptive radiation. Even though adaptive radiation is the most iconic process in the diversification of life (most famously in the Galapagos finches), most well-studied cases occur on islands, and we know relatively little about how or if these radiations occur on continents, where most species actually live. In the absence of obvious barriers like oceanic waters, how does diversification proceed across the continuous geography of a continent? Does it start in one region, slowly spreading out as species adapt to each new habitat in turn, or does it spread everywhere quickly, and only evolve adaptations later? In their study, Schenk and Steppan develop a new approach to examine how speciation proceeds across geographic space by studying 300 species from one of the most diverse groups of mammals, the South American sigmodontine rodents. Sigmodontines experienced an adaptive radiation following their colonization from North America approximately seven million years ago. Soon after colonizing South America, they expanded into many new regions quickly at the same time as they had a burst of diversification, and their dispersal across the heterogeneous landscape was important to their adaptive radiation. As time passed, both the rate of geographic dispersal and speciation slowed down in concert. While ecological divergence into different niches is important during adaptive radiations, movement into new and distinctive geographic regions allows speciation to repeatedly reoccur and can promote the remarkable biodiversity characteristic of adaptive radiations. Abstract Although the importance of biogeography in the speciation process is well-recognized, the fundamental role of geographic diversification during adaptive radiations has not been studied to determine its importance during the adaptive radiation process. We examined the relationship between lineage and regional diversification patterns in the South American rodent subfamily Sigmodontinae, one of the best candidates for an adaptive radiation in mammals, to propose a conceptual framework for geographic transitions during adaptive radiations. We reconstructed a time-calibrated phylogeny from four nuclear and one mitochondrial gene for 77% of sigmodontine diversity. Historical biogeography was reconstructed among 14 regions, to which we applied a sliding-window approach to estimate regional transition rates through time. We compared these rate patterns and measured whether regions consisted of species that were more phylogenetically related than expected by chance. Following the initial South American colonization around 7 million years ago, multiple expansions from northern regions correlated with a burst of speciation. Subsequently, both diversification and regional transition rates decreased overall and within the majority of regions. Despite high regional transition rates, nearly all regional assemblages were phylogenetically clustered, indicating within-region diversification was common. We conclude that biogeographic complexity and partitioning played a profound role in the adaptive radiation of the South American Sigmodontinae (Oryzomyalia), the degree to which is determined by the relative scales of spatial variation and dispersal abilities. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699221 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699221">Read the Article</a></i> </p> --> <p><b>Biogeographic transitions are important drivers of species diversity in adaptive radiations </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;">T</span>o explain why millions of species exist on Earth, biologists seek to discover how species evolve and the factors promoting diversification. Of particular interest are groups of closely related species that rapidly evolved many new species as they adapted to new niches, a process called adaptive radiation. Even though adaptive radiation is the most iconic process in the diversification of life (most famously in the Galapagos finches), most well-studied cases occur on islands, and we know relatively little about how or if these radiations occur on continents, where most species actually live. In the absence of obvious barriers like oceanic waters, how does diversification proceed across the continuous geography of a continent? Does it start in one region, slowly spreading out as species adapt to each new habitat in turn, or does it spread everywhere quickly, and only evolve adaptations later?</p> <p>In their study, Schenk and Steppan develop a new approach to examine how speciation proceeds across geographic space by studying 300 species from one of the most diverse groups of mammals, the South American sigmodontine rodents. Sigmodontines experienced an adaptive radiation following their colonization from North America approximately seven million years ago. Soon after colonizing South America, they expanded into many new regions quickly at the same time as they had a burst of diversification, and their dispersal across the heterogeneous landscape was important to their adaptive radiation. As time passed, both the rate of geographic dispersal and speciation slowed down in concert. While ecological divergence into different niches is important during adaptive radiations, movement into new and distinctive geographic regions allows speciation to repeatedly reoccur and can promote the remarkable biodiversity characteristic of adaptive radiations.</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;">A</span>lthough the importance of biogeography in the speciation process is well-recognized, the fundamental role of geographic diversification during adaptive radiations has not been studied to determine its importance during the adaptive radiation process. We examined the relationship between lineage and regional diversification patterns in the South American rodent subfamily Sigmodontinae, one of the best candidates for an adaptive radiation in mammals, to propose a conceptual framework for geographic transitions during adaptive radiations. We reconstructed a time-calibrated phylogeny from four nuclear and one mitochondrial gene for 77% of sigmodontine diversity. Historical biogeography was reconstructed among 14 regions, to which we applied a sliding-window approach to estimate regional transition rates through time. We compared these rate patterns and measured whether regions consisted of species that were more phylogenetically related than expected by chance. Following the initial South American colonization around 7 million years ago, multiple expansions from northern regions correlated with a burst of speciation. Subsequently, both diversification and regional transition rates decreased overall and within the majority of regions. Despite high regional transition rates, nearly all regional assemblages were phylogenetically clustered, indicating within-region diversification was common. We conclude that biogeographic complexity and partitioning played a profound role in the adaptive radiation of the South American Sigmodontinae (Oryzomyalia), the degree to which is determined by the relative scales of spatial variation and dispersal abilities.</p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 28 Jun 2018 05:00:00 GMT “Competition and ‘stragglers’ as mediators of developmental synchrony in periodical cicadas” https://amnat.org/an/newpapers/OctBlackwood-A.html Read the ArticleAbstract Periodical cicadas are enigmatic organisms: broods spanning large spatial ranges consist of developmentally synchronized populations of 3-4 sympatric species that emerge as adults every 13 or 17 years. Only one brood typically occupies any single location, with well-defined boundaries separating distinct broods. The cause of such synchronous development remains uncertain but it is known that synchronous emergence of large numbers of adults in a single year satiates predators, allowing a substantial fraction of emerging adults to survive long enough to reproduce. Competition among nymphs feeding on tree roots almost certainly plays a role in limiting populations. However, due to the difficulty of working with such long-lived subterranean life stages, the mechanisms governing competition in periodical cicadas have not been identified. A second process that may affect synchrony among periodical cicadas is their ability to delay or accelerate their emergence as adults by one year and accelerate it by four years (“stragglers”). We develop a non-linear Leslie-type matrix model that describes cicada dynamics accounting for predation, competition and stragglers. Using numerical simulations, we identify conditions that generate dynamics in which a single brood occupies a given geographical location. Our results show that while stragglers have potential for introducing multiple sympatric broods, the interaction of interbrood competition with predation-driven Allee effects creates a system resistant to such invasions and populations maintain developmental synchrony. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699255">Read the Article</a><!-- <p><i><a href="https://dx.doi.org/10.1086/699255">Read the Article</a></i> </p> --></p><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">P</span>eriodical cicadas are enigmatic organisms: broods spanning large spatial ranges consist of developmentally synchronized populations of 3-4 sympatric species that emerge as adults every 13 or 17 years. Only one brood typically occupies any single location, with well-defined boundaries separating distinct broods. The cause of such synchronous development remains uncertain but it is known that synchronous emergence of large numbers of adults in a single year satiates predators, allowing a substantial fraction of emerging adults to survive long enough to reproduce. Competition among nymphs feeding on tree roots almost certainly plays a role in limiting populations. However, due to the difficulty of working with such long-lived subterranean life stages, the mechanisms governing competition in periodical cicadas have not been identified. A second process that may affect synchrony among periodical cicadas is their ability to delay or accelerate their emergence as adults by one year and accelerate it by four years (&ldquo;stragglers&rdquo;). We develop a non-linear Leslie-type matrix model that describes cicada dynamics accounting for predation, competition and stragglers. Using numerical simulations, we identify conditions that generate dynamics in which a single brood occupies a given geographical location. Our results show that while stragglers have potential for introducing multiple sympatric broods, the interaction of interbrood competition with predation-driven Allee effects creates a system resistant to such invasions and populations maintain developmental synchrony.</p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 28 Jun 2018 05:00:00 GMT “Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in the frog Crinia georgiana” https://amnat.org/an/newpapers/OctRudinB-A.html Read the Article Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in a frog Abstract When organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog Crinia georgiana, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low-water) late in larval development. We then estimated the contribution of additive and non-additive sources of genetic variation to early offspring fitness under both environments. Our results revealed a marked decline in larval fitness under the stressful (low-water) rearing environment, but also that additive genetic variation was negligible for all traits. However, in most cases we found significant sire-by-dam interactions, indicating the importance of non-additive genetic variation for offspring fitness. Moreover, sire-by-dam interactions were modified by the treatment, indicating that patterns of non-additive genetic variance depend on environmental context. For all traits, we found higher levels of non-additive genetic variation (relative to total phenotypic variation) when larvae were reared under stressful conditions, suggesting that the fitness costs associated with incompatible parental crosses (e.g. homozygous deleterious recessive alleles) will only be expressed when water availability is low. Taken together, our results highlight the need to consider patterns of non-additive genetic variation under contrasting selective regimes when considering the resilience of species to environmental change. More forthcoming papers &raquo; <p><i><a href="https://dx.doi.org/10.1086/699231">Read the Article</a></i> </p> <p><b>Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in a frog </b></p><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">W</span>hen organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog <i>Crinia georgiana</i>, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low-water) late in larval development. We then estimated the contribution of additive and non-additive sources of genetic variation to early offspring fitness under both environments. Our results revealed a marked decline in larval fitness under the stressful (low-water) rearing environment, but also that additive genetic variation was negligible for all traits. However, in most cases we found significant sire-by-dam interactions, indicating the importance of non-additive genetic variation for offspring fitness. Moreover, sire-by-dam interactions were modified by the treatment, indicating that patterns of non-additive genetic variance depend on environmental context. For all traits, we found higher levels of non-additive genetic variation (relative to total phenotypic variation) when larvae were reared under stressful conditions, suggesting that the fitness costs associated with incompatible parental crosses (e.g. homozygous deleterious recessive alleles) will only be expressed when water availability is low. Taken together, our results highlight the need to consider patterns of non-additive genetic variation under contrasting selective regimes when considering the resilience of species to environmental change.</p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 28 Jun 2018 05:00:00 GMT “Coevolution slows the disassembly of mutualistic networks” https://amnat.org/an/newpapers/OctNuismer2018-A.html Read the Article Disassembly of mutualistic networks is slowed by historical coevolution and mitigated by coevolutionary rescue Abstract Important groups of mutualistic species are threatened worldwide, and identifying factors that make them more or less fragile in the face of disturbance is becoming increasingly critical. Although much research has focused on identifying the ecological factors that favor the stability of communities rich in mutualists, much less has been devoted to understanding the role of historical and contemporary evolution. Here we develop mathematical models and computer simulations of coevolving mutualistic communities that allow us to explore the importance of coevolution in stabilizing communities against anthropogenic disturbance. Our results demonstrate that communities with a long history of coevolution are substantially more robust to disturbance, losing individual species and interactions at lower rates. In addition, our results identify a novel phenomenon – coevolutionary rescue – that mitigates the impacts of ongoing anthropogenic disturbance by re-wiring the network structure of the community in a way that compensates for the extinction of individual species and interactions. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699218"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699218">Read the Article</a></i> </p> --> <p><b>Disassembly of mutualistic networks is slowed by historical coevolution and mitigated by coevolutionary rescue </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>mportant groups of mutualistic species are threatened worldwide, and identifying factors that make them more or less fragile in the face of disturbance is becoming increasingly critical. Although much research has focused on identifying the ecological factors that favor the stability of communities rich in mutualists, much less has been devoted to understanding the role of historical and contemporary evolution. Here we develop mathematical models and computer simulations of coevolving mutualistic communities that allow us to explore the importance of coevolution in stabilizing communities against anthropogenic disturbance. Our results demonstrate that communities with a long history of coevolution are substantially more robust to disturbance, losing individual species and interactions at lower rates. In addition, our results identify a novel phenomenon – coevolutionary rescue – that mitigates the impacts of ongoing anthropogenic disturbance by re-wiring the network structure of the community in a way that compensates for the extinction of individual species and interactions. </p> <div style="float: right;"><a href="https://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 28 Jun 2018 05:00:00 GMT