ASN RSS https://amnat.org/ Latest press releases and announcements from the ASN en-us Wed, 20 Jan 2021 06:00:00 GMT 60 “Pathogen dynamics across the diversity of ageing” https://amnat.org/an/newpapers/Feb-Clark.html Jessica Clark, Luke McNally, and Tom J. Little (Feb 2021) Host ageing can modulate epidemiological dynamics Read the Article (Just Accepted) Populations are often made up of individuals of different ages. These individuals of different ages often have different reproductive capabilities, risks of dying and susceptibilities to infection. Reproduction, mortality and susceptibility are also important aspects of infectious disease dynamics. Despite these parallels, and how common it is for populations to be age-structured, little research has explored how characteristics of population age structure, and specifically individual ageing can impact disease spread. Researchers at the University of Edinburgh took an interdisciplinary approach in addressing these questions. First, using the freshwater crustacean Daphnia magna, they carried out two experiments. The results show that the process of ageing within a single organism is not unidirectional. For example, whilst old mothers produce fewer offspring with an increase in their age, those offspring from old mothers performed equally or indeed better than offspring from young mothers, across a suite of traits including susceptibility to infection. Drawing on these experimental observations, they then developed a deterministic age-structured mathematical model that showed that age-specific susceptibility, maternal effects on offspring susceptibility, age-specific rates of reproduction and age-specific rates of mortality, can all affect infectious disease dynamics in direct and indirect ways. Using this model, they also showed that these dynamics are dependent on the ecological conditions experienced by the population, most noticeably the pressure of extrinsic mortality (for example, harvesting or rapid environmental change). In light of the rapid rate of human population age seen globally, the model was finally used to ask how slowing the process of ageing in humans (or those showing a similar ageing profile) could affect infectious disease dynamics, showing that an increase in lifespan without an increase in healthspan could increase disease transmission. Abstract Reproduction, mortality and immune function often change with age, but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the ageing spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an ageing profile of a single organism, including traits directly linked to pathogen susceptibility, and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of ageing produce dramatically different transmission landscapes: in many cases ageing can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics, or the potential repercussions of senescence manipulation. More forthcoming papers &raquo; <p>Jessica Clark, Luke McNally, and Tom J. Little (Feb 2021) </p> <p><b>Host ageing can modulate epidemiological dynamics </b></p> <p><i><a href="https://dx.doi.org/10.1086/712380">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>opulations are often made up of individuals of different ages. These individuals of different ages often have different reproductive capabilities, risks of dying and susceptibilities to infection. Reproduction, mortality and susceptibility are also important aspects of infectious disease dynamics. Despite these parallels, and how common it is for populations to be age-structured, little research has explored how characteristics of population age structure, and specifically individual ageing can impact disease spread. Researchers at the University of Edinburgh took an interdisciplinary approach in addressing these questions. First, using the freshwater crustacean <i>Daphnia magna</i>, they carried out two experiments. The results show that the process of ageing within a single organism is not unidirectional. For example, whilst old mothers produce fewer offspring with an increase in their age, those offspring from old mothers performed equally or indeed better than offspring from young mothers, across a suite of traits including susceptibility to infection. Drawing on these experimental observations, they then developed a deterministic age-structured mathematical model that showed that age-specific susceptibility, maternal effects on offspring susceptibility, age-specific rates of reproduction and age-specific rates of mortality, can all affect infectious disease dynamics in direct and indirect ways. Using this model, they also showed that these dynamics are dependent on the ecological conditions experienced by the population, most noticeably the pressure of extrinsic mortality (for example, harvesting or rapid environmental change). In light of the rapid rate of human population age seen globally, the model was finally used to ask how slowing the process of ageing in humans (or those showing a similar ageing profile) could affect infectious disease dynamics, showing that an increase in lifespan without an increase in healthspan could increase disease transmission. </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>eproduction, mortality and immune function often change with age, but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the ageing spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an ageing profile of a single organism, including traits directly linked to pathogen susceptibility, and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of ageing produce dramatically different transmission landscapes: in many cases ageing can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics, or the potential repercussions of senescence manipulation. </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, 29 Dec 2020 06:00:00 GMT “Comparison of categorical color perception in two Estrildid finches” https://amnat.org/an/newpapers/Feb-Caves.html Eleanor M. Caves, Patrick A. Green, Matthew N. Zipple, Dhanya Bharath, Susan Peters, S&ouml;nke Johnsen, and Stephen Nowicki (Feb 2021) Categorical color perception differs between two finches that differ in coloration and may be adapted for signal function Read the ArticleThe essential role of animal signals in interactions such as mate choice and aggression suggests that sensory systems might be adapted to perceive signal stimuli that are particularly salient for a given species. Many finches in the family Estrildidae display colorful signaling traits; for example, male zebra finches (Taeniopygia guttata) display carotenoid-based beak coloration, ranging from light orange to dark red, and females evaluate male beak coloration during mate choice. Prior work has shown that female zebra finches perceive this orange-red color range in a categorical fashion. That is, even though male beak color varies along a continuum from most orange to most red, females perceive this variation as simply either “orange” or “red.” Is categorical perception a general feature of how birds in this group see colors, or has selection acted on the perceptual system of zebra finches in particular due to the important signaling function of orange-red coloration in this species? In this study, researchers from Duke University examined whether female Bengalese finches (Lonchura striata domestica), an estrildid finch having black, brown and white plumage and lacking any carotenoid coloration, also perceives the orange-red color range tested previously with zebra finches in a categorical fashion. The researchers found no evidence for categorical perception of orange-red coloration in Bengalese finches. Follow up experiments then showed that, in Bengalese finches, the ability to discriminate between two colors is dictated primarily by the difference in brightness between those colors, rather than whether colors fall in certain categories. In zebra finches, however, the importance of brightness differences in color discrimination depends upon whether two colors come from the same or different categories. The results of this study are consistent with the hypothesis that selection on a signaling system may act on the perceptual systems of the signal receivers. It remains to be seen, however, whether the expression of categorical perception correlates consistently with the use of color signals across a broader range of species such as the clade of estrildid finches. The work also lends insight into the potential mechanisms underlying the phenomenon of categorical color perception in birds, and perhaps in other vertebrates as well. Abstract Sensory systems are predicted to be adapted to the perception of important stimuli, such as signals used in communication. Prior work has shown that female zebra finches perceive the carotenoid-based orange-red coloration of male beaks—a mate choice signal—categorically. Specifically, females exhibited an increased ability to discriminate between colors from opposite sides of a perceptual category boundary than equally-different colors from the same side of the boundary. The Bengalese finch, an Estrildid finch related to the zebra finch, is black, brown and white, lacking carotenoid coloration. To explore the relationship between categorical color perception and signal use, we tested Bengalese finches using the same orange-red continuum as in zebra finches, and also tested how both species discriminated among colors differing systematically in hue and brightness. Unlike in zebra finches, we found no evidence of categorical perception of an orange-red continuum in Bengalese finches. Instead, we found that the combination of chromatic distance (hue difference) and Michelson contrast (difference in brightness) strongly correlated with color discrimination ability on all tested color pairs in Bengalese finches. The pattern was different in zebra finches: this strong correlation held only when discriminating between colors from different categories, but not when discriminating between colors from within the same category. These experiments suggest that categorical perception is not a universal feature of avian, or even Estrildid finch, vision. Our findings also provide further insights into the mechanism underlying categorical perception and are consistent with the hypothesis that categorical perception is adapted for signal perception. More forthcoming papers &raquo; <p>Eleanor M. Caves, Patrick A. Green, Matthew N. Zipple, Dhanya Bharath, Susan Peters, S&ouml;nke Johnsen, and Stephen Nowicki (Feb 2021)</p> <p><b>Categorical color perception differs between two finches that differ in coloration and may be adapted for signal function</b></p> <p><i><a href="https://dx.doi.org/10.1086/712379">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;">T</span>he essential role of animal signals in interactions such as mate choice and aggression suggests that sensory systems might be adapted to perceive signal stimuli that are particularly salient for a given species. Many finches in the family Estrildidae display colorful signaling traits; for example, male zebra finches (<i>Taeniopygia guttata</i>) display carotenoid-based beak coloration, ranging from light orange to dark red, and females evaluate male beak coloration during mate choice. Prior work has shown that female zebra finches perceive this orange-red color range in a categorical fashion. That is, even though male beak color varies along a continuum from most orange to most red, females perceive this variation as simply either “orange” or “red.” </p><p>Is categorical perception a general feature of how birds in this group see colors, or has selection acted on the perceptual system of zebra finches in particular due to the important signaling function of orange-red coloration in this species? In this study, researchers from Duke University examined whether female Bengalese finches (<i>Lonchura striata domestica</i>), an estrildid finch having black, brown and white plumage and lacking any carotenoid coloration, also perceives the orange-red color range tested previously with zebra finches in a categorical fashion. The researchers found no evidence for categorical perception of orange-red coloration in Bengalese finches. Follow up experiments then showed that, in Bengalese finches, the ability to discriminate between two colors is dictated primarily by the difference in brightness between those colors, rather than whether colors fall in certain categories. In zebra finches, however, the importance of brightness differences in color discrimination depends upon whether two colors come from the same or different categories. </p><p>The results of this study are consistent with the hypothesis that selection on a signaling system may act on the perceptual systems of the signal receivers. It remains to be seen, however, whether the expression of categorical perception correlates consistently with the use of color signals across a broader range of species such as the clade of estrildid finches. The work also lends insight into the potential mechanisms underlying the phenomenon of categorical color perception in birds, and perhaps in other vertebrates as well. </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>ensory systems are predicted to be adapted to the perception of important stimuli, such as signals used in communication. Prior work has shown that female zebra finches perceive the carotenoid-based orange-red coloration of male beaks—a mate choice signal—categorically. Specifically, females exhibited an increased ability to discriminate between colors from opposite sides of a perceptual category boundary than equally-different colors from the same side of the boundary. The Bengalese finch, an Estrildid finch related to the zebra finch, is black, brown and white, lacking carotenoid coloration. To explore the relationship between categorical color perception and signal use, we tested Bengalese finches using the same orange-red continuum as in zebra finches, and also tested how both species discriminated among colors differing systematically in hue and brightness. Unlike in zebra finches, we found no evidence of categorical perception of an orange-red continuum in Bengalese finches. Instead, we found that the combination of chromatic distance (hue difference) and Michelson contrast (difference in brightness) strongly correlated with color discrimination ability on all tested color pairs in Bengalese finches. The pattern was different in zebra finches: this strong correlation held only when discriminating between colors from different categories, but not when discriminating between colors from within the same category. These experiments suggest that categorical perception is not a universal feature of avian, or even Estrildid finch, vision. Our findings also provide further insights into the mechanism underlying categorical perception and are consistent with the hypothesis that categorical perception is adapted for signal perception. </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, 29 Dec 2020 06:00:00 GMT “Kin blackmail as a coercive route to altruism” https://amnat.org/an/newpapers/Feb-Kennedy.html Patrick Kennedy and Andrew N. Radford (Feb 2021) Blackmail can lead to altruism evolving at payoff values that would otherwise be against Hamilton’s rule Read the Article Raising kids can be tough. Sometimes, you need all the help you can get. But what can you do if your family aren’t interested? In this study, researchers at the University of Bristol suggest that animals might be able to blackmail relatives into becoming helpers. Recently, there has been renewed interest in how manipulation could drive the evolution of ‘altruism’ (personal sacrifices to help others) among animals. However, the focus has been on recipients limiting options for potential helpers, such as by impairing their abilities to reproduce. A more Machiavellian manipulation may also be possible: a recipient may deliberately limit its own options, holding its own fitness hostage to helpers’ behaviors. In a Darwinian sense, relatives are valuable to individuals to the extent that they are vehicles for shared genes. Whether helping evolves depends on a simple cost–benefit calculation known as ‘Hamilton’s rule’: help if it will lead to a net increase in copies of your genes in the population. However, one aspect of Hamilton’s rule has been overlooked: individuals might increase their value to kin by ensuring that shared genes will be in jeopardy if reluctant relatives fail to help. The authors use kin selection models to extend the theory of ‘blackmail’ (first suggested four decades ago by Israeli biologist Amotz Zahavi) to the evolution of altruism beyond parental care. Shrewd use of energy reserves may be a promising focus to uncover blackmail empirically. For instance, if two tasks are required for the kids to survive, a mother could lay a large clutch but invest most of her energy in only one task. She has tied her hands: unless relatives step in to complete the other task, the babies will not leave the nest alive. Blackmailed altruism might often give the illusion of harmonious cooperation, since helpers would appear to be making completely voluntary choices to help. In reality, a sly form of coercion would underlie the apparent harmony: make your family an offer they simply can’t refuse. Abstract The evolution of altruism (helping a recipient at personal cost) often involves conflicts of interest. Recipients frequently prefer greater altruism than actors are prepared to provide. Coercion by recipients normally involves limiting an actor’s options. Here, we consider the possibility of a coercive recipient limiting its own options. Forty years ago, Amotz Zahavi suggested that nesting birds may be ‘blackmailed’ into increased parental care if offspring threaten to harm themselves (and so jeopardize the direct fitness of their parents). In a simple kin selection model, we expand blackmail to indirect fitness, and highlight that blackmail can occur between any kin to drive reproductive division of labor. In principle, a recipient may place its own fitness at risk (brinkmanship), imposing sanctions on a relative’s indirect fitness if the relative fails to cooperate. To use its own survival or reproduction as leverage in a sequential game, a recipient must increase the extent to which its existing fitness depends on the actor’s behavior and so credibly commit to a cost if the actor does not comply. As it requires opportunities for commitment, kin blackmail can arise only under stringent conditions, but existing kin blackmailers may pass unnoticed due to their strategic success. More forthcoming papers &raquo; <p>Patrick Kennedy and Andrew N. Radford (Feb 2021)</p> <p><b>Blackmail can lead to altruism evolving at payoff values that would otherwise be against Hamilton&rsquo;s rule </b></p> <p><i><a href="https://dx.doi.org/10.1086/712349">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;">R</span>aising kids can be tough. Sometimes, you need all the help you can get. But what can you do if your family aren’t interested? In this study, researchers at the University of Bristol suggest that animals might be able to blackmail relatives into becoming helpers. </p><p>Recently, there has been renewed interest in how manipulation could drive the evolution of ‘altruism’ (personal sacrifices to help others) among animals. However, the focus has been on recipients limiting options for potential helpers, such as by impairing their abilities to reproduce. A more Machiavellian manipulation may also be possible: a recipient may deliberately limit its <i>own</i> options, holding its own fitness hostage to helpers’ behaviors. </p><p>In a Darwinian sense, relatives are valuable to individuals to the extent that they are vehicles for shared genes. Whether helping evolves depends on a simple cost–benefit calculation known as ‘Hamilton’s rule’: help if it will lead to a net increase in copies of your genes in the population. However, one aspect of Hamilton’s rule has been overlooked: individuals might increase their value to kin by ensuring that shared genes will be in jeopardy if reluctant relatives fail to help. The authors use kin selection models to extend the theory of ‘blackmail’ (first suggested four decades ago by Israeli biologist Amotz Zahavi) to the evolution of altruism beyond parental care. </p><p>Shrewd use of energy reserves may be a promising focus to uncover blackmail empirically. For instance, if two tasks are required for the kids to survive, a mother could lay a large clutch but invest most of her energy in only one task. She has tied her hands: unless relatives step in to complete the other task, the babies will not leave the nest alive. </p><p>Blackmailed altruism might often give the illusion of harmonious cooperation, since helpers would appear to be making completely voluntary choices to help. In reality, a sly form of coercion would underlie the apparent harmony: make your family an offer they simply can’t refuse. </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 evolution of altruism (helping a recipient at personal cost) often involves conflicts of interest. Recipients frequently prefer greater altruism than actors are prepared to provide. Coercion by recipients normally involves limiting an actor’s options. Here, we consider the possibility of a coercive recipient limiting its own options. Forty years ago, Amotz Zahavi suggested that nesting birds may be ‘blackmailed’ into increased parental care if offspring threaten to harm themselves (and so jeopardize the direct fitness of their parents). In a simple kin selection model, we expand blackmail to indirect fitness, and highlight that blackmail can occur between any kin to drive reproductive division of labor. In principle, a recipient may place its own fitness at risk (brinkmanship), imposing sanctions on a relative’s indirect fitness if the relative fails to cooperate. To use its own survival or reproduction as leverage in a sequential game, a recipient must increase the extent to which its existing fitness depends on the actor’s behavior and so credibly commit to a cost if the actor does not comply. As it requires opportunities for commitment, kin blackmail can arise only under stringent conditions, but existing kin blackmailers may pass unnoticed due to their strategic success. </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, 29 Dec 2020 06:00:00 GMT “Frugivory specialization in birds and fruit chemistry structure mutualistic networks across the Neotropics” https://amnat.org/an/newpapers/Feb-Pizo.html Marco A. Pizo, Juan M. Morales, Otso Ovaskainen, and Tom&aacute;s A. Carlo (Feb&nbsp;2021) New paper shows the importance of fruit chemistry as a factor structuring the interactions between frugivores and plants Read the ArticleThe issue of fruit choice by fruit-eating animals has long intrigued ecologists. With such a variety of fruits available out there, how do frugivorous animals chose a given fruit to eat? This is not a trivial question as fruit eating is at the same time the final act of a long evolutionary history that enabled frugivores and fruits to interact with each other, and the first step of the process that led to the dispersal of seeds and regeneration of plant populations. We know that fruit morphology is part of the answer, but other fruit traits should also be considered. Lipid content varies a lot in fruits and is, interestingly, negatively correlated with sugar content. Compared to sugars, lipids demand longer processing in the gut to be absorbed. Scattered published observations and the experience accumulated by Marco Pizo and Tomas Carlo with fruits and frugivores in the field has provided evidence that lipid-rich and lipid-poor (sugary) fruits might attract different bird species. They formally tested this possibility by compiling from the literature over 35 thousand feeding visits of 317 bird species to 165 fleshy-fruited plant species. The analytical expertise of Juan Morales and Otso Ovaskainen was pivotal in analyzing this huge dataset to reveal that the relative contribution of predominantly insectivorous birds (which also eat some fruit) to feeding visits to lipid-rich fruits is higher than birds that include a greater amount of fruits in the diet, while the reverse is true for lipid-poor fruits. The digestive physiology of predominantly insectivorous birds adapted to deal with arthropods that normally are richer in lipids than fruits likely permits them to process lipid-rich fruits, while the rapid food passage typical of heavily frugivorous species makes lipid-poor fruits better suited to them. This balance between the degree of frugivory of birds and the pattern of visitation to lipid-poor and lipid-rich fruits helps to illuminate community-wide interactions between frugivorous birds and plants. Abstract The interaction between fruit chemistry and the physiological traits of frugivores is expected to shape the structure of mutualistic seed dispersal networks, but it has been understudied compared to the role of morphological trait-matching in structuring interaction patterns. For instance, highly frugivorous birds (i.e., birds that have fruits as the main component of their diets), which characteristically have fast gut-passage times, are expected to avoid feeding on lipid-rich fruits because of the long gut-retention times associated with lipid digestion. Here we compiled data from 84 studies conducted in the Neotropics that used focal-plant methods to record 35,815 feeding visits made by 317 bird species (155 genera in 28 families) on 165 plant species (82 genera in 48 families). We investigated the relationship between the degree of frugivory of birds (i.e., how much of their diet is composed by fruit) at the genus level and their visits to plant genera that vary in fruit-lipid content. We used a Hierarchical Modeling of Species Communities approach that accounted for the effects of differences in body size, the bird and plant phylogeny, and the spatial location of study sites. We found that birds with low degree of frugivory (e.g., predominantly insectivores) tend to have the highest increase in visitation rates as fruits get more lipid-rich, while birds that are more frugivorous tend to increase visits at a lower rate or even decrease visitation rates as lipids increase in fruits. This balance between degree of frugivory and visitation rates to lipid-poor and lipid-rich fruits provides a mechanism to explain specialized dispersal systems and the occurrence of certain physiological-nutritional filters, ultimately helping to understand community-wide interaction patterns between birds and plants. A especialização na dieta das aves e a química dos frutos estruturam as redes de frugivoria nos Neotrópicos Apesar de potencialmente influenciar a estrutura das redes de interações entre animais frugívoros e frutos carnosos, as características químicas dos frutos e a fisiologia digestiva dos frugívoros tem sido pouco estudada em comparação com o papel de características morfológicas na estruturação dos padrões de interação. Por exemplo, aves altamente frugívoras (ou seja, aves que têm os frutos como principal componente de suas dietas), que caracteristicamente processam rapidamente os frutos no intestino, devem evitar frutos ricos em lipídios que demandam longo tempo de retenção intestinal para sua completa digestão. Para testar esta hipótese, compilamos dados de 84 estudos conduzidos nos Neotrópicos que registraram 35.815 visitas de alimentação feitas por 317 espécies de aves (155 gêneros, 28 famílias) em 165 espécies de plantas (82 gêneros, 48 famílias). Investigamos a relação entre o grau de frugivoria das aves (ou seja, quanto de sua dieta é composta por frutos) em nível de gênero e a frequência de suas visitas a gêneros de plantas que variaram quanto ao teor de lipídeos dos frutos. Usamos uma abordagem de Modelagem Hierárquica de Comunidades que levou em consideração os efeitos das diferenças no tamanho do corpo, da filogenia das aves e plantas e da localização das áreas de estudo. As aves com baixo grau de frugivoria (por exemplo, predominantemente insetívoros) tendem a aumentar a taxa de visitas à medida que os frutos se tornam mais ricos em lipídios, enquanto as taxas de visita das aves mais frugívoras tendem a aumentar menos ou mesmo diminuir à medida que aumenta o conteúdo lipídico dos frutos. Esse balanço entre o grau de frugivoria das aves e a frequência de alimentação em frutos pobres e ricos em lipídios representa um mecanismo para explicar os sistemas especializados de dispersão de sementes e a ocorrência de filtros fisiológicos-nutricionais que ajudam a entender os padrões de interação entre as aves frugívoras e as plantas. More forthcoming papers &raquo; <p>Marco A. Pizo, Juan M. Morales, Otso Ovaskainen, and Tom&aacute;s A. Carlo (Feb&nbsp;2021)</p> <p><b>New paper shows the importance of fruit chemistry as a factor structuring the interactions between frugivores and plants </b></p> <p><i><a href="https://www.journals.uchicago.edu/doi/10.1086/712381">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;">T</span>he issue of fruit choice by fruit-eating animals has long intrigued ecologists. With such a variety of fruits available out there, how do frugivorous animals chose a given fruit to eat? This is not a trivial question as fruit eating is at the same time the final act of a long evolutionary history that enabled frugivores and fruits to interact with each other, and the first step of the process that led to the dispersal of seeds and regeneration of plant populations. We know that fruit morphology is part of the answer, but other fruit traits should also be considered. Lipid content varies a lot in fruits and is, interestingly, negatively correlated with sugar content. Compared to sugars, lipids demand longer processing in the gut to be absorbed. Scattered published observations and the experience accumulated by Marco Pizo and Tomas Carlo with fruits and frugivores in the field has provided evidence that lipid-rich and lipid-poor (sugary) fruits might attract different bird species. They formally tested this possibility by compiling from the literature over 35 thousand feeding visits of 317 bird species to 165 fleshy-fruited plant species. The analytical expertise of Juan Morales and Otso Ovaskainen was pivotal in analyzing this huge dataset to reveal that the relative contribution of predominantly insectivorous birds (which also eat some fruit) to feeding visits to lipid-rich fruits is higher than birds that include a greater amount of fruits in the diet, while the reverse is true for lipid-poor fruits. The digestive physiology of predominantly insectivorous birds adapted to deal with arthropods that normally are richer in lipids than fruits likely permits them to process lipid-rich fruits, while the rapid food passage typical of heavily frugivorous species makes lipid-poor fruits better suited to them. This balance between the degree of frugivory of birds and the pattern of visitation to lipid-poor and lipid-rich fruits helps to illuminate community-wide interactions between frugivorous birds and plants.</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 interaction between fruit chemistry and the physiological traits of frugivores is expected to shape the structure of mutualistic seed dispersal networks, but it has been understudied compared to the role of morphological trait-matching in structuring interaction patterns. For instance, highly frugivorous birds (i.e., birds that have fruits as the main component of their diets), which characteristically have fast gut-passage times, are expected to avoid feeding on lipid-rich fruits because of the long gut-retention times associated with lipid digestion. Here we compiled data from 84 studies conducted in the Neotropics that used focal-plant methods to record 35,815 feeding visits made by 317 bird species (155 genera in 28 families) on 165 plant species (82 genera in 48 families). We investigated the relationship between the degree of frugivory of birds (i.e., how much of their diet is composed by fruit) at the genus level and their visits to plant genera that vary in fruit-lipid content. We used a Hierarchical Modeling of Species Communities approach that accounted for the effects of differences in body size, the bird and plant phylogeny, and the spatial location of study sites. We found that birds with low degree of frugivory (e.g., predominantly insectivores) tend to have the highest increase in visitation rates as fruits get more lipid-rich, while birds that are more frugivorous tend to increase visits at a lower rate or even decrease visitation rates as lipids increase in fruits. This balance between degree of frugivory and visitation rates to lipid-poor and lipid-rich fruits provides a mechanism to explain specialized dispersal systems and the occurrence of certain physiological-nutritional filters, ultimately helping to understand community-wide interaction patterns between birds and plants. </p><h4>A especialização na dieta das aves e a química dos frutos estruturam as redes de frugivoria nos Neotrópicos</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>pesar de potencialmente influenciar a estrutura das redes de interações entre animais frugívoros e frutos carnosos, as características químicas dos frutos e a fisiologia digestiva dos frugívoros tem sido pouco estudada em comparação com o papel de características morfológicas na estruturação dos padrões de interação. Por exemplo, aves altamente frugívoras (ou seja, aves que têm os frutos como principal componente de suas dietas), que caracteristicamente processam rapidamente os frutos no intestino, devem evitar frutos ricos em lipídios que demandam longo tempo de retenção intestinal para sua completa digestão. Para testar esta hipótese, compilamos dados de 84 estudos conduzidos nos Neotrópicos que registraram 35.815 visitas de alimentação feitas por 317 espécies de aves (155 gêneros, 28 famílias) em 165 espécies de plantas (82 gêneros, 48 famílias). Investigamos a relação entre o grau de frugivoria das aves (ou seja, quanto de sua dieta é composta por frutos) em nível de gênero e a frequência de suas visitas a gêneros de plantas que variaram quanto ao teor de lipídeos dos frutos. Usamos uma abordagem de Modelagem Hierárquica de Comunidades que levou em consideração os efeitos das diferenças no tamanho do corpo, da filogenia das aves e plantas e da localização das áreas de estudo. As aves com baixo grau de frugivoria (por exemplo, predominantemente insetívoros) tendem a aumentar a taxa de visitas à medida que os frutos se tornam mais ricos em lipídios, enquanto as taxas de visita das aves mais frugívoras tendem a aumentar menos ou mesmo diminuir à medida que aumenta o conteúdo lipídico dos frutos. Esse balanço entre o grau de frugivoria das aves e a frequência de alimentação em frutos pobres e ricos em lipídios representa um mecanismo para explicar os sistemas especializados de dispersão de sementes e a ocorrência de filtros fisiológicos-nutricionais que ajudam a entender os padrões de interação entre as aves frugívoras e as plantas. </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, 29 Dec 2020 06:00:00 GMT