Akçay, Erol
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Publication Group Size and Social Conflict in Complex Societies(2014-02-01) Shen, Sheng-Feng; Akçay, Erol; Rubenstein, Dustin RConflicts of interest over resources or reproduction among individuals in a social group have long been considered to result in automatic and universal costs to group living. However, exploring how social conflict varies with group size has produced mixed empirical results. Here we develop a model that generates alternative predictions for how social conflict should vary with group size depending on the type of benefits gained from being in a social group. We show that a positive relationship between social conflict and group size is favored when groups form primarily for the benefits of sociality but not when groups form mainly for accessing group-defended resources. Thus, increased social conflict in animal societies should not be viewed as an automatic cost of larger social groups. Instead, studying the relationship between social conflict and the types of grouping benefits will be crucial for understanding the evolution of complex societies.Publication Pathways to Social Evolution: Reciprocity, Relatedness, and Synergy(2014-08-01) Van Cleve, Jeremy; Akçay, ErolMany organisms live in populations structured by space and by class, exhibit plastic responses to their social partners, and are subject to nonadditive ecological and fitness effects. Social evolution theory has long recognized that all of these factors can lead to different selection pressures but has only recently attempted to synthesize how these factors interact. Using models for both discrete and continuous phenotypes, we show that analyzing these factors in a consistent framework reveals that they interact with one another in ways previously overlooked. Specifically, behavioral responses (reciprocity), genetic relatedness, and synergy interact in nontrivial ways that cannot be easily captured by simple summary indices of assortment. We demonstrate the importance of these interactions by showing how they have been neglected in previous synthetic models of social behavior both within and between species. These interactions also affect the level of behavioral responses that can evolve in the long run; proximate biological mechanisms are evolutionarily stable when they generate enough responsiveness relative to the level of responsiveness that exactly balances the ecological costs and benefits. Given the richness of social behavior across taxa, these interactions should be a boon for empirical research as they are likely crucial for describing the complex relationship linking ecology, demography, and social behavior.Publication The Perfect Family: Decision Making in Biparental Care(2009-10-13) Akçay, Erol; Roughgarden, JoanBackground Previous theoretical work on parental decisions in biparental care has emphasized the role of the conflict between evolutionary interests of parents in these decisions. A prominent prediction from this work is that parents should compensate for decreases in each other's effort, but only partially so. However, experimental tests that manipulate parents and measure their responses fail to confirm this prediction. At the same time, the process of parental decision making has remained unexplored theoretically. We develop a model to address the discrepancy between experiments and the theoretical prediction, and explore how assuming different decision making processes changes the prediction from the theory. Model Description We assume that parents make decisions in behavioral time. They have a fixed time budget, and allocate it between two parental tasks: provisioning the offspring and defending the nest. The proximate determinant of the allocation decisions are parents' behavioral objectives. We assume both parents aim to maximize the offspring production from the nest. Experimental manipulations change the shape of the nest production function. We consider two different scenarios for how parents make decisions: one where parents communicate with each other and act together (the perfect family), and one where they do not communicate, and act independently (the almost perfect family). Conclusions/Significance The perfect family model is able to generate all the types of responses seen in experimental studies. The kind of response predicted depends on the nest production function, i.e. how parents' allocations affect offspring production, and the type of experimental manipulation. In particular, we find that complementarity of parents' allocations promotes matching responses. In contrast, the relative responses do not depend on the type of manipulation in the almost perfect family model. These results highlight the importance of the interaction between nest production function and how parents make decisions, factors that have largely been overlooked in previous models.Publication Social Inheritance Can Explain the Structure of Animal Social Networks(2015-01-01) Ilany, Amiyaal; Akçay, ErolThe social network structure of animal populations has major implications to survival, reproductive success, sexual selection, and pathogen transmission. Recent studies showed in various species that the structure of social networks and individuals’ positions in it are influenced by individual traits such as sex, age, and social rank, and can be heritable between generations. But as of yet, no general theory of social network structure exists that can explain the diversity of social networks observed in nature, and serve as a null model for detecting species and population-specific factors. Here we propose such a general model of social network structure. We consider the emergence of network structure as a result of two types of social bond formation: via social inheritance, in which newborns are likely to bond with maternal contacts, and via forming bonds randomly. We compare model output to data from several species, showing that it can generate networks with properties such as those observed in real social systems. Our model demonstrates that some of the observed properties of social networks, such as heritability of network position or assortative associations, can be understood as a consequence of social inheritance. Our results highlight the need to consider the dynamic processes that generate social structure in order to explain patterns of variation in social networks.Publication Biological Institutions: The Political Science of Animal Cooperation(2013-07-01) Akçay, Erol; Roughgarden, Joan; Fearon, James; Ferejohn, John; Weingast, Barry RSocial evolution is one of the most rapidly developing areas in evolutionary biology. A main theme is the emergence of cooperation among organisms, including the factors that impede cooperation. Although animal societies seem to have no formal institutions, such as courts or legislatures, we argue that biology presents many examples where an interaction can properly be thought of as an informal institution, meaning there are evolved norms and structure to the interaction that enable parties to reach mutually beneficial outcomes. These informal institutions are embedded in the natural history of the interaction, in factors such as where and when parties interact, how long and how close they stay together, and so on. Institutional theory thus widens the scope of behavioral ecology by considering not only why animals evolve to choose the strategies they choose, but also asking both why it is that they find themselves in those particular interaction setups and how these particular interactions can be sustained. Institutions frequently enable interacting parties avoid inefficient outcomes and support efficient exchange among agents with conflicting interests. The main thesis of this paper is that the organization of many biological interactions can properly be understood as institutions that enable mutually beneficial outcomes to be achieved relative to an unstructured interaction. To do this, institutions resolve or regulate the conflicts of interests among parties. The way conflicts of interests affect the outcome depends on the structure of the interaction, which can create problems of commitment, coordination and private information. Institutional theory focuses on how to address each of these issues, typically focusing on the development of social norms, rules, and other constraints on individual behaviors. We illustrate our thesis with examples from cooperative breed and genes as within-body-mechanism-design.Publication Water Stress Strengthens Mutualism Among Ants, Trees, and Scale Insects(2013-11-05) Pringle, Elizabeth G; Akçay, Erol; Raab, Ted K; Dirzo, Rodolfo; Gordon, Deborah MAbiotic environmental variables strongly affect the outcomes of species interactions. For example, mutualistic interactions between species are often stronger when resources are limited. The effect might be indirect: water stress on plants can lead to carbon stress, which could alter carbon-mediated plant mutualisms. In mutualistic ant–plant symbioses, plants host ant colonies that defend them against herbivores. Here we show that the partners' investments in a widespread ant–plant symbiosis increase with water stress across 26 sites along a Mesoamerican precipitation gradient. At lower precipitation levels, Cordia alliodora trees invest more carbon in Azteca ants via phloem-feeding scale insects that provide the ants with sugars, and the ants provide better defense of the carbon-producing leaves. Under water stress, the trees have smaller carbon pools. A model of the carbon trade-offs for the mutualistic partners shows that the observed strategies can arise from the carbon costs of rare but extreme events of herbivory in the rainy season. Thus, water limitation, together with the risk of herbivory, increases the strength of a carbon-based mutualism.Publication Behavioral Responses in Structured Populations Pave the Way to Group Optimality(2012-02-01) Akçay, Erol; Van Cleve, JeremyAn unresolved controversy regarding social behaviors is exemplified when natural selection might lead to behaviors that maximize fitness at the social-group level but are costly at the individual level. Except for the special case of groups of clones, we do not have a general understanding of how and when group-optimal behaviors evolve, especially when the behaviors in question are flexible. To address this question, we develop a general model that integrates behavioral plasticity in social interactions with the action of natural selection in structured populations. We find that group-optimal behaviors can evolve, even without clonal groups, if individuals exhibit appropriate behavioral responses to each other’s actions. The evolution of such behavioral responses, in turn, is predicated on the nature of the proximate behavioral mechanisms. We model a particular class of proximate mechanisms, prosocial preferences, and find that such preferences evolve to sustain maximum group benefit under certain levels of relatedness and certain ecological conditions. Thus, our model demonstrates the fundamental interplay between behavioral responses and relatedness in determining the course of social evolution. We also highlight the crucial role of proximate mechanisms such as prosocial preferences in the evolution of behavioral responses and in facilitating evolutionary transitions in individuality.Publication New Approaches to the Evolution of Social Behavior(2009-04-01) Akçay, ErolOne of the most fascinating topics in evolutionary biology is how and why organisms cooperate with each other. Natural selection works through competition between alleles for representation in the next generation. Yet one sees everywhere organisms actually helping each other, from mutualisms between ants and plants to the altruistic acts of firefighters storming into burning buildings to rescue people. But how can natural selection lead to cooperation? This, of course, is not a new question, and a tremendous amount of work in evolutionary theory in the last 40 years has shown that helping others can frequently be the winning strategy in the struggle for existence. We have a sophisticated theory of social evolution, dealing not only with helping behaviors, but also other behaviors such as policing, spiteful harm-doing, and so on.Publication Negotiation, Sanctions, and Context Dependency in the Legume-Rhizobium Mutualism(2011-07-01) Akçay, Erol; Simms, Ellen LTwo important questions about mutualisms are how the fitness costs and benefits to the mutualist partners are determined and how these mechanisms affect the evolutionary dynamics of the mutualism. We tackle these questions with a model of the legumerhizobium symbiosis that regards the mutualism outcome as a result of biochemical negotiations between the plant and its nodules. We explore the fitness consequences of this mechanism to the plant and rhizobia and obtain four main results. First, negotiations permit the plant to differentially reward more-cooperative rhizobia—a phenomenon termed “plant sanctions”—but only when more-cooperative rhizobia also provide the plant with good outside options during negotiations with other nodules. Second, negotiations may result in seemingly paradoxical cases where the plant is worse off when it has a “choice” between two strains of rhizobia than when infected by either strain alone. Third, even when sanctions are effective, they are by themselves not sufficient to maintain cooperative rhizobia in a population: less cooperative strains always have an advantage at the population level. Finally, partner fidelity feedback, together with genetic correlations between a rhizobium strain’s cooperativeness and the outside options it provides, can maintain cooperative rhizobia. Our results show how joint control over the outcome of a mutualism through the proximate mechanism of negotiation can affect the evolutionary dynamics of interspecific cooperation.Publication Evolutionary Models of Mutualism(2015-01-01) Akçay, Erol