Search

Animals, and mammals in particular, vary widely in their "pace of life," with some species living long lives and reproducing infrequently (slow life histories) and others living short lives and reproducing often (fast life histories). These species also vary in the importance of maternal care in offspring fitness: In some species, offspring are fully independent of their mothers following a brief period of nutritional input, while others display a long period of continued dependence on mothers well after nutritional dependence. Here, we hypothesize that these two axes of variation are causally related to each other, such that extended dependence of offspring on maternal presence leads to the evolution of longer lives at the expense of reproduction. We use a combination of deterministic modeling and stochastic agent-based modeling to explore how empirically observed links between maternal survival and offspring fitness are likely to shape the evolution of mortality and fertility. Each of our modeling approaches leads to the same conclusion: When maternal survival has a strong impact on the survival of offspring and grandoffspring, populations evolve longer lives with less frequent reproduction. Our results suggest that the slow life histories of humans and other primates as well as other long-lived, highly social animals such as hyenas, whales, and elephants are partially the result of the strong maternal care that these animals display. We have designed our models to be readily parameterized with demographic data that are routinely collected by long-term researchers, which will facilitate more thorough testing of our hypothesis. [ABSTRACT FROM AUTHOR]

Although social group size and stability are key areas of interest for studying the evolution and maintenance of animal societies, the evolution of group membership control and how that affects the resulting group size have not been fully explored. Here we develop a game-theoretical model that considers how social and ecological factors jointly affect the resolution of conflict over group size between current group members (insiders) and potential joiners (outsiders). Our model predicts that group size will more closely approach the optimum for insiders when the potential conflict between insiders and outsiders is large, as well as when the cost of engaging in social conflict is high. We also show that the joining effort, repelling effort, cost of selfishness and genetic relatedness have interacting effects on conflict resolution between insiders and outsiders and, thus, on expected group size and structure. Our model further predicts that the expected group size will increase as genetic relatedness between insiders and an outsider increases, assuming that the direct fitness cost for insiders to accept an outsider is relatively large or that the benefit to the outsider joining is small. Ultimately, our model synthesizes previous insider–outsider conflict models to generate a framework for understanding the evolution of both group membership control and the size and structure of the resulting social groups. • A game-theoretical model helps understand the continuum of group membership control. • Our model predicts that closely related insiders invest more in repelling efforts. • The model emphasizes studying the effect of relatedness on expected group size. • We offer alternative explanations for the evolution of nonkin groups. • Our predictions help study the insider-outsider conflict during group formation. [ABSTRACT FROM AUTHOR]

Many animals are able to perform recognition feats that astound us--such as a rodent recognizing kin it has never met. Yet in other contexts, animals appear clueless as when reed warblers rear cuckoo chicks that bear no resemblance to their own species. Failures of recognition when it would seem adaptive have been especially puzzling. Here, we present a simple tug-of-war game theory model examining how individuals should optimally invest in affecting the accuracy of discrimination between desirable and undesirable recipients. In the game, discriminating individuals (operators) and desirable and undesirable recipients (targets and mimics, respectively) can all invest effort into their own preferred outcome. We demonstrate that stable inaccurate recognition will arise when undesirable recipients have large fitness gains from inaccurate recognition relative to the pay-offs that the other two parties receive from accurate recognition. The probability of accurate recognition is often determined by just the relative pay-offs to the desirable and undesirable recipients, rather than to the discriminator. Our results provide a new lens on long-standing puzzles including a lack of nepotism in social insect colonies, tolerance of brood parasites and male birds caring for extra-pair young in their nests, which our model suggests should often lack accurate discrimination. [ABSTRACT FROM AUTHOR]

Sandra Vehrencamp's (1983)Animal Behaviour paper provided a rigorous mathematical foundation for understanding reproductive partitioning within animal societies by focusing on the limits to reproductive competition over reproductive shares among group members. The central idea is that the degree of inequity in reproductive shares is limited by the option of group members to leave the group and reproduce elsewhere. This central idea has been retained in extensions of her model, and unification of these extensions with rival models has been developed to accommodate new data and alternative starting assumptions. Although some criticism has been directed towards skew theory, as presented both in the original Vehrencamp model and in subsequent syntheses, we show that many of these criticisms have been misguided. Synthetic skew theory, with Vehrencamp’s model as its cornerstone, stands as our most general and complete, yet still largely untested, framework for understanding the evolutionary forces shaping the evolution of reproductive partitioning in animal societies. [ABSTRACT FROM AUTHOR]

Summary: Queen monogamy is ancestral among bees, ants, and wasps (Order Hymenoptera), and the close relatedness that it generates within colonies is considered key for the evolution of eusociality in these lineages [1]. Paradoxically, queens of several eusocial species are extremely promiscuous [2], a derived behavior that decreases relatedness among workers and fitness gained from rearing siblings but benefits queens by enhancing colony productivity [3–9] and inducing workers to rear queens’ sons instead of less related worker-derived males [10–13]. Selection for promiscuity would be especially strong if productivity in a singly inseminated queen’s colony declined because selfish workers invested in personal reproduction at the expense of performing tasks that contribute to colony productivity. We show in honey bees that workers’ ovaries are more developed when queens are singly rather than multiply inseminated and that increasing ovary activation is coupled with reductions in task performance by workers and colony-wide rates of foraging and waggle-dance recruitment. Increased investment in reproductive physiology by selfish workers might result from greater incentive for them to favor worker-derived males or because low mating frequency signals a queen’s diminished quality or future fecundity. Either possibility fosters selection for queen promiscuity, revealing a novel benefit of it for eusocial insects. [Copyright &y& Elsevier]

Individuals of different quality often differ in their helping behavior, but sometimes it is the high-quality individuals who help most (e.g., human meat sharing, vigilance) and other times it is the low-quality individuals (e.g., reproductive queues, primate grooming). We argue that these differences depend on individual differences in the performance costs of actually helping, the opportunity costs from forsaking alternative activities, and the fitness benefits for engaging the help. If helping is more difficult for some individuals to do (quality-dependent help), it will usually be done by high-quality individuals, whereas help that all individuals could do equally well (quality-independent help) will be done by whoever pays lower opportunity costs. Our model makes novel predictions about many kinds of helping, allows us to categorize different types of helping by their relationship with individual quality, and is general enough to apply to many situations. Furthermore, it can be generalized to any other type of (nonhelping) behavior where there are individual differences in benefits, performance costs, or opportunity costs. [ABSTRACT FROM PUBLISHER]

The evolution of cooperation among nonkin remains a puzzle, and almost no theoretical work has examined the timing of altruism, that is, when a behavior that benefits others at one's own fitness expense should be expressed in time. We present an evolutionary dynamic-game model to address the question of when, if ever, an altruist would voluntarily emerge in time in groups of non- relatives. Our model shows that when the benefit of having an altruistic leader decays with time, leaders will eventually emerge and will emerge later (i) in larger groups, (ii) when the cost of leadership increases, and (iii) when the assessment interval increases. The model applies to diverse situations in which time-decaying group benefits are obtained only after a group member assumes a leadership role at some cost to itself, including leader roles in foraging flocks and migration groups in birds and spiny lobsters and in high-risk foraging in desert ants. [ABSTRACT FROM AUTHOR]

Surveys of insect societies have revealed four key, recurring organizational trends: (i) The most elaborated cooperation occurs in groups of relatives. (ii) Cooperation is typically more elaborate in species with large colony sizes than in species with small colony sizes, the latter exhibiting greater internal reproductive conflict and lesser morphological and behavioral specialization. (iii) Within a species, per capita brood output typically declines as colony size increases. (iv). The ecological factors of resource patchiness and intergroup competition are associated with the most elaborated cooperation. Predictions of all four patterns emerge elegantly from a game-theoretic model in which within-group tug-of-wars are nested within a between-group tug-of-war. In this individual selection model, individuals are faced with the problem of how to partition their energy between investment in intercolony competition versus investment in intracolony competition, i.e., internal tugs-of-war over shares of the resources gained through intergroup competition. An individual's evolutionarily stable investment in between-group competition (i.e., within-group cooperation) versus within-group competition is shown to increase as within-group relatedness increases, to decrease as group size increases (for a fixed number of competing groups), to increase as the number of competing groups in a patch increases, and to decrease as between-group relatedness increases. Moreover, if increasing patch richness increases both the number of individuals within a group and the number of competing groups, greater overall cooperation within larger groups will be observed. The model presents a simple way of determining quantitatively how intergroup conflict will propel a society forward along a ‘superorganism continuum.’ [ABSTRACT FROM AUTHOR]

Abstract: When resources are patchily distributed in an environment, behavioral ecologists frequently turn to ideal free distribution (IFD) models to predict the spatial distribution of organisms. In these models, predictions about distributions depend upon two key factors: the quality of habitat patches and the nature of competition between consumers. Surprisingly, however, no IFD models have explored the possibility that consumers modulate their competitive efforts in an evolutionarily stable manner. Instead, previous models assume that resource acquisition ability and competition are fixed within species or within phenotypes. We explored the consequences of adaptive modulation of competitive effort by incorporating tug-of-war theory into payoff equations from the two main classes of IFD models (continuous input (CI) and interference). In the models we develop, individuals can increase their share of the resources available in a patch, but do so at the costs of increased resource expenditures and increased negative interactions with conspecifics. We show how such models can provide new hypotheses to explain what are thought to be deviations from IFDs (e.g., the frequent observation of fewer animals than predicted in “good” patches of habitat). We also detail straightforward predictions made uniquely by the models we develop, and we outline experimental tests that will distinguish among alternatives. [Copyright &y& Elsevier]

Reproductive skew models attempt to predict the fraction of reproduction contributed by each individual that participates in a communal brood. One potential limitation of these models is that individuals make a single, fixed decision about group membership and reproductive allocation at the beginning of the breeding period. While this is appropriate for animals that reproduce in a synchronous bout, many cooperative breeders produce offspring over a prolonged period of time. It is likely that these species adjust reproductive allocation and group membership over time in response to temporal shifts in group productivity and ecological constraints. In this paper we adapt transactional models of reproductive skew to a continuous form, generating time-dependent functions of reproductive allocation. We derive a general method for predicting temporal changes in group membership as well as a general expression for reproductive skew across the regions over which a group is stable. Using a linear approximation for time-dependent reproduction, we derive new expressions for reproductive skew in cases where the subordinate departs during the breeding period. In this case we find that the traditional model always overestimates the subordinate's share of reproduction when dominants are in control of both reproductive shares and group membership (i.e., concessions models). Conversely, we find that the traditional model always underestimates the subordinate's share of reproduction when subordinates are in control of reproductive shares (i.e., constraint models). We discuss the implications of these new calculations in relation to the traditional skew models and more recent empirical tests of reproductive skew in animal societies. [ABSTRACT FROM AUTHOR]

For decades, evolutionary biologists and anthropologists have puzzled over the negative relationship that exists between wealth and fertility in humans. Particularly mystifying have been that (1) humans do not appear to translate their reproductive resources into additional offspring, and (2) attempts to model natural selection resulting in a negative relationship between amount of economic resources and fertility have all predicted the opposite relationship. In this article, we use game theory to derive the evolutionarily stable ratio of offspring investment versus resource generation when the continuing survival of offspring lineages is strongly affected by long-term resource accumulation. The model generates the prediction that fertility should be lower when there are more resources available and when more intensive investment in resource generation has the potential to acutely increase the survival probability of descendant offspring lineages. This prediction provides a simple and general evolutionary explanation for why fertility negatively correlates with wealth both within and between human populations. Indeed, this may provide a new understanding of low fertility in contemporary human groups in addition to furthering our understanding the demographic transition in general. [ABSTRACT FROM AUTHOR]

We propose a new, evolutionary, game-theoretic model of conditional human mating strategies that integrates currently disconnected bodies of data into a single mathematically-explicit theory of human mating transactions. The model focuses on the problem of how much resource a male must provide to a female to secure and retain her as a mate. By using bidding-game models, we show how the male's minimally required resource incentive varies as a function of his own mate value, the value of the female, and the distribution of the mate values of their available alternative mates. The resulting theory parsimoniously accounts for strategic pluralism within the sexes, mate choice differences between the sexes, and assortative mating, while generating a rich set of testable new predictions about human mating behavior. [ABSTRACT FROM AUTHOR]

Optimal-skew models (OSMs) predict that cooperative breeding occurs as a result of dominants conceding reproductive benefits to subordinates, and that division of reproduction within groups reflects each cooperator's willingness and ability to contest aggressively for dominance. Polistine paper wasps are a leading model system for testing OSMs, and data on reproduction and aggression appear to support OSMs. These studies, however, measure aggression as a single rate rather than by the activity patterns of individuals. This leads to a potential error: if individuals are more likely to receive aggression when active than when inactive, differences in aggression across samples can reflect changes in activity rather than hostility. This study replicates a field manipulation cited as strongly supporting OSMs. We show that fundamentally different conclusions arise when controlling for individual activity states. Our analyses strongly suggest that behaviours classified as 'aggression' in paper wasps are unlikely to function in establishing, maintaining or responding to changes in reproductive skew. This illustrates that OSM tests using aggression or other non-reproductive behaviour as a metric for reproductive partitioning must demonstrate those links rather than assume them. [ABSTRACT FROM AUTHOR]

Evolutionary psychology provides a cogent metatheory for psychological science. It has furnished compelling theories of major domains of human functioning, including mating, parenting, kinship, morality, cooperation, conflict, aggression, and aesthetics. It has produced hundreds of empirical discoveries missed entirely by prior psychologists. Developmental dynamics, properly conceived, can add to the theoretical foundation of evolutionary psychology. But it has not provided alternative theories capable of explaining the many detailed empirical discoveries made by evolutionary psychologists. Nor has it generated a comparable bounty of new empirical discoveries. By critical scientific standards-theoretical cogency, predictive accuracy, interdisciplinary consistency, and empirical harvest-modern evolutionary psychology fares well compared with alternatives. [ABSTRACT FROM AUTHOR]

Queens of the paper wasp Polistes dominulus have the option to found nests in spring alone or together with other queens. In the latter case a dominance hierarchy is established among the cofoundresses with the dominant wasp getting the major share of the reproductive output of the nest. The different reproductive strategies of an individual wasp will necessitate different behaviors. We measured the volumes of brain structures as a potential indicator of differential use and elaboration of a number of brain structures. We found a significant increase in the volume of the antennal lobe in members of multiple foundress associations in comparison to single foundresses. The volume of the collar, a substructure of the calyx of the mushroom body, was also significantly larger, especially in the dominant queen of a foundress association. No significant differences between dominant or subordinate wasps in regard to volume of the measured brain substructures were found.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Describes the models of the reproductive skew theory that are tested on social insects. Predictions of the models of the reproductive skew theory; Results of the tests of the models in insect social groups; Extensions to the concession theory that are important for interpreting skew data in social insects.

Presents a study which provide evidence that early females in the temperate, eusocial paper wasp Polistes fuscatus disperse as future nest foundresses instead of staying and helping at their natal nests. Methodology; Determinants of early nest tenure; Results.

Optimal skew models explain reproductive sharing within social groups as resulting from reproductive incentives given by controlling dominants to subordinates in return for peaceful cooperation. We explore two versions of an alternative, the incomplete control model, for the evolution of reproductive sharing within groups. In this model, dominants have only limited control over the allocation of reproduction and must expend effort to increase their share of the total group output We show that, when the relatedness between dominant and subordinate is symmetrical, (1) the subordinate's fraction of reproduction either increases with, or is insensitive to, the subordinate's genetic relatedness, r, to the dominant in both versions of the incomplete control model, whereas the subordinate's fraction of reproduction decreases with increasing r in the optimal skew model, (2) the subordinate's share of reproduction in the incomplete control model must exceed that in the optimal skew model, and (3) ecological factors affecting solitary breeding success do not directly affect the subordinate's share of reproduction in incomplete control model but do in the optimal skew model. When dominant-subordinate relatedness is asymmetrical (as is often the case in parent-offspring associations), the incomplete control model predicts no reproduction by the subordinate offspring regardless of group size for groups containing any mixture of unrelated and full-sibling subordinates, whereas the optimal skew models predict that such reproduction is possible when the group size is three or more. The available evidence indicates a negative relationship between relatedness and a subordinate's reproductive share in both vertebrate and hymenopteran societies, apparently supporting the predictions of the optimal skew, not incomplete control, class of models. However, such a negative relationship is not necessarily inconsistent with the incomplete control model when, as is true for some vertebrate studies, it results from a comparison of skews in genetically monogamous, nonincestuous groups of parents and their offspring (asymmetric relatednesses) with skews in groups of nonkin (symmetric relatednesses). Both models predict higher skews in parent-offspring associations. Occasional reproduction by subordinate offspring in groups of asymmetrical relatedness when such groups are larger than dyads is more consistent with the optimal skew model, however. Overall, current data on reproductive skew and its relationships to intragroup aggression and ecological constraints support the optimal skew model, but more data are needed to rule out the incomplete control model. These models are examples of two different general views of intrasocietal evolution: the tug-of-war view, in which group members engage in a struggle over resources, and the transactional view, in which group members exchange parcels of reproduction to induce beneficial behavior from each other. [ABSTRACT FROM AUTHOR]

Females of the arctiid moth Utetheisa ornatrix mate preferentially with larger males, receiving both direct phenotypic and indirect genetic benefits[SUP 1]. Here we demonstrate that the female's mating preference is inherited through the father rather than the mother, indicating that the preference gene or genes lie mostly or exclusively on the Z sex chromosome, which is strictly paternally inherited by daughters. Furthermore, we show that the preferred male trait and the female preference for that trait are correlated, as females with larger fathers have a stronger preference for larger males. These findings are predicted by the protected invasion theory[SUP 2,3], which asserts that male homogametic sex chromosome systems (ZZ/ZW) found in lepidopterans and birds promote the evolution of exaggerated male traits through sexual selection. Specifically, the theory predicts that, because female preference alleles arising on the Z chromosome are transmitted to all sons that have the father's attractive trait rather than to only a fraction of the sons, such alleles will experience stronger positive selection and be less vulnerable to chance loss than would autosomal alleles. [ABSTRACT FROM AUTHOR]

How do organisms balance different types of recognition errors when cues associated with desirable and undesirable individuals or resources overlap? This is a fundamental question of signal detection theory (SDT). As applied in sociobiology, SDT is not limited to a single context or animal taxon, therefore its application can span what may be considered dissimilar systems. One of the applications of SDT is the suite of acceptance threshold models proposed by Reeve (1989), which analysed how individuals should balance acceptance and rejection errors in social discrimination decisions across a variety of recognition contexts, distinguished by how these costs and benefits relatively combine. We conducted a literature review to evaluate whether these models' specific predictions have been upheld. By examining over 350 research papers, we quantify how Reeve's models (Reeve 1989 Am. Nat. 133, 407-435 (doi:10.1086/284926)) have influenced the field of ecological and behavioural recognition systems research. We found overall empirical support for the predictions of the specific models proposed by Reeve, and argue for further expansion of their applications into more diverse taxonomic and additional recognition contexts. [ABSTRACT FROM AUTHOR]

Social interactions are mediated by recognition systems, meaning that the cognitive abilities or phenotypic diversity that facilitate recognition may be common targets of social selection. Recognition occurs when a receiver compares the phenotypes produced by a sender with a template. Coevolution between sender and receiver traits has been empirically reported in multiple species and sensory modalities, though the dynamics and relative exaggeration of traits from senders versus receivers have received little attention. Here, we present a coevolutionary dynamic model that examines the conditions under which senders and receivers should invest effort in facilitating individual recognition. The model predicts coevolution of sender and receiver traits, with the equilibrium investment dependent on the relative costs of signal production versus cognition. In order for recognition to evolve, initial sender and receiver trait values must be above a threshold, suggesting that recognition requires some degree of pre-existing diversity and cognitive abilities. The analysis of selection gradients demonstrates that the strength of selection on sender signals and receiver cognition is strongest when the trait values are furthest from the optima. The model provides new insights into the expected strength and dynamics of selection during the origin and elaboration of individual recognition, an important feature of social cognition in many taxa. [ABSTRACT FROM AUTHOR]

Abstract: Two major challenges exist when empirically testing the predictions of sperm allocation theory. First, the study species must adhere to the assumptions of the model being tested. Unfortunately, the common assumption of sperm allocation models that females mate a maximum of once or twice does not hold for many, if not most, multiply and sequentially mating animals. Second, a model's parameters, which dictate its predictions, must be measured in the study species. Common examples of such parameters, female mating frequency and sperm precedence patterns, are unknown for many species used in empirical tests. Here, we present a broadly applicable model, appropriate for multiply, sequentially mating animals, and test it in three species for which data on all the relevant parameter values are available. The model predicts that relative allocation to virgin females, compared to nonvirgins, depends on the interaction between female mating rate and the sperm precedence pattern: relative allocation to virgins increases with female mating rate under first‐male precedence, while the opposite is true under later‐male precedence. Our model is moderately successful in predicting actual allocation patterns in the three species, including a cricket in which we measured the parameter values and performed an empirical test of allocation. [ABSTRACT FROM AUTHOR]

Reports on mathematical models devised by G. Roberts and T.N. Sherratt for cooperation that take into account the fact that, in biological situations, the choice is not always as clear-cut as whether or not to cooperate. Theoretical work on the evolution of altruism between unrelated individuals being dominated by the so-called prisoner's dilemma model.

Recognition systems play a central role in mediating cooperative behavior among individuals in a population. Despite the importance of discriminating among potential recipients of cooperation, the evolutionary forces that maintain diversity in traits used for kin recognition are poorly understood. Greenbeard-based models of kin recognition in which alleles for cooperative behavior also control recognition of those alleles in potential cooperators suggest that discrimination based on a greenbeard locus leads to positive frequency dependence, eroding diversity at the very genes responsible for recognition. As a result, the phenotypic diversity used for kin recognition has been widely assumed to be cues rather than signals of genetic identity. Diversity in identity cues is maintained by selection on other traits for reasons unrelated to recognition. A major problem with greenbeard-based models is that greenbeard recognition systems are uncommon among animals, which tend to learn kin phenotypes. We develop a simple model showing that learning a kin recognition template is sufficient to increase and maintain diversity in genetic traits used for kin recognition. Thus, our results suggest that phenotypes used for recognition may be true signals of genetic identity. As such, phenotypes are expected to evolve to facilitate recognition. Increased diversity in genetically-based recognition signals is also predicted to initiate a positive feedback loop between recognition efficiency and levels of cooperation. Finally, we discuss how the genetic architecture of recognition traits may influence kin discrimination abilities. [ABSTRACT FROM AUTHOR]

Given the costs of multiple mating, why has female polyandry evolved? Utetheisa ornatrix moths are well suited for studying multiple mating in females because females are highly polyandrous over their life span, with each male mate transferring a substantial spermatophore with both genetic and nongenetic material. The accumulation of resources might explain the prevalence of polyandry in this species, but another, not mutually exclusive, possibility is that females mate multiply to increase the probability that their sons will inherit more-competitive sperm. This latter 'sexy-sperm' hypothesis posits that female multiple mating and male sperm competitiveness coevolve via a Fisherian runaway process. We tested the sexy-sperm hypothesis by using competitive double matings to compare the sperm competition success of sons of polyandrous versus monandrous females. In accordance with sexy-sperm theory, we found that in 511 offspring across 17 families, the male whose polyandrous mother mated once with each of three different males sired significantly more of all total offspring (81%) than did the male whose monandrous mother was mated thrice to a single male. Interestingly, sons of polyandrous mothers had a significantly biased sex ratio of their brood toward sons, also in support of the hypothesis. [ABSTRACT FROM AUTHOR]

Honey bee workers have few opportunities for direct reproduction because their ovary development is chemically suppressed by queens and worker-laid eggs are destroyed by workers. While workers with fully developed ovaries are rare in honey bee colonies, we show that partial ovary development is common. Across nine studies, an average of 6% to 43% of workers had partially developed ovaries in queenright colonies with naturally mated queens. This shift by workers toward potential future reproduction is linked to lower productivity, which suggests that even small investments in reproductive physiology by selfish workers reduce cooperation below a theoretical maximum. Furthermore, comparisons across 26 species of bees and wasps revealed that the level of partial ovary development in honey bees is similar to that of other eusocial Hymenoptera where there is reproductive conflict among colony members. Natural variation in the extent of partial ovary development in honey bee colonies calls for an exploration of the genetic and ecological factors that modulate shifts in cooperation within animal societies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Engagement of a large public in domestic conservation actions can have a large impact. [•] New gains can be made using the Web to build support for environmental stewardship. [•] Evolutionary and social psychology tell us how to generate cooperation the Web. [•] Combining social networking with citizen-mapping can harness the power of the crowd. [•] Communications fostering group-identity or group-efficacy can motivate people to act. [•] Visibility of actions, norms, reputations, and benchmarks can increase cooperation. [Copyright &y& Elsevier]

Members of social groups face a trade-off between investing selfish effort for themselves and investing cooperative effort to produce a shared group resource. Many group resources are shared equitably: they may be intrinsically non-excludable public goods, such as vigilance against predators, or so large that there is little cost to sharing, such as cooperatively hunted big game. However, group members' personal resources, such as food hunted individually, may be monopolizable. In such cases, an individual may benefit by investing effort in taking others' personal resources, and in defending one's own resources against others. We use a game theoretic “tug-of-war” model to predict that when such competition over personal resources is possible, players will contribute more towards a group resource, and also obtain higher payoffs from doing so. We test and find support for these predictions in two laboratory economic games with humans, comparing people's investment decisions in games with and without the options to compete over personal resources or invest in a group resource. Our results help explain why people cooperatively contribute to group resources, suggest how a tragedy of the commons may be avoided, and highlight unifying features in the evolution of cooperation and competition in human and non-human societies. [ABSTRACT FROM AUTHOR]

Social organisms in many taxa cooperate to produce resources that are shared among group members. Some cooperatively produced resources may be monopolized by individuals who invest in within-group competition, but these have largely been overlooked in empirical and theoretical research on human cooperation, which has focused on noncontestable public goods. In this study, we allow for the potential of within-group competition over cooperatively produced resources and use a game theoretic “tug-of-war” model and empirical test to show that such competition decreases the degree of cooperation within human groups and hence decreases group members' payoffs. Our study thus sheds light on how cooperative production and equal division of shared resources may have evolved, expands on current models of human cooperation to reflect the many natural conditions with opportunities for within-group competition, and demonstrates unifying principles in cooperation and competition across the animal kingdom. [ABSTRACT FROM PUBLISHER]

We develop and apply a simple model for animal communication in which signalers can use a nontrivial frequency of deception without causing listeners to completely lose belief. This common feature of animal communication has been difficult to explain as a stable adaptive outcome of the options and payoffs intrinsic to signaling interactions. Our theory is based on two realistic assumptions. (1) Signals are ‘overheard’ by several listeners or listener types with different payoffs. The signaler may then benefit from using incomplete honesty to elicit different responses from different listener types, such as attracting potential mates while simultaneously deterring competitors. (2) Signaler and listener strategies change dynamically in response to current payoffs for different behaviors. The dynamic equations can be interpreted as describing learning and behavior change by individuals or evolution across generations. We explain how our dynamic model differs from other solution concepts from classical and evolutionary game theory and how it relates to general models for frequency-dependent phenotype dynamics. We illustrate the theory with several applications where deceptive signaling occurs readily in our framework, including bluffing competitors for potential mates or territories. We suggest future theoretical directions to make the models more general and propose some possible experimental tests. [ABSTRACT FROM AUTHOR]

Estimating paternity and genetic relatedness is central to many empirical and theoretical studies of social insects. The two important measures of a queen's mating number are her actual number of mates and her effective number of mates. Estimating the effective number of mates is mathematically identical to the problem of estimating the effective number of alleles in population genetics, a common measure of genetic variability introduced by ). We derive a new bias-corrected estimator of effective number of types (mates or alleles) and compare this new method to previous methods for estimating true and effective numbers of types using Monte Carlo simulations. Our simulation results suggest that the examined estimators of the true number of types have very similar statistical properties, whereas the estimators of effective number of types have quite different statistical properties. Moreover, our new proposed estimator of effective number of types is approximately unbiased, and has considerably lower variance than the original estimator. Our new method will help researchers more accurately estimate intracolony genetic relatedness of social insects, which is an important measure in understanding their ecology and social behaviour. It should also be of use in population genetic studies in which the effective number of alleles is of interest. [ABSTRACT FROM AUTHOR]

Cooperation is widespread both within and between species, but are intraspecific and interspecific cooperation fundamentally similar or qualitatively different phenomena? This review evaluates this question, necessary for a general understanding of the evolution of cooperation. First, we outline three advantages of cooperation relative to noncooperation (acquisition of otherwise inaccessible goods and services, more efficient acquisition of resources, and buffering against variability), and predict when individuals should cooperate with a conspecific versus a heterospecific partner to obtain these advantages. Second, we highlight five axes along which heterospecific and conspecific partners may differ: relatedness and fitness feedbacks, competition and resource use, resource-generation abilities, relative evolutionary rates, and asymmetric strategy sets and outside options. Along all of these axes, certain asymmetries between partners are more common in, but not exclusive to, cooperation between species, especially complementary resource use and production. We conclude that cooperation within and between species share many fundamental qualities, and that differences between the two systems are explained by the various asymmetries between partners. Consideration of the parallels between intra- and interspecific cooperation facilitates application of well-studied topics in one system to the other, such as direct benefits within species and kin-selected cooperation between species, generating promising directions for future research. [ABSTRACT FROM AUTHOR]

When there is conspicuous underexploitation of a limited resource, it is worth asking, what mechanisms allow presumably valuable resources to be left unused? Evolutionary biologists have generated a wide variety of hypotheses to explain this, ranging from interdemic group selection to selfishly prudent individual restraint. We consider a situation in which, despite high intraspecific competition, individuals leave most of a key resource unexploited. The parasitic wasp that does this finds virtually all host egg clusters in a landscape but parasitizes only about a third of the eggs in each and then leaves a deterrent mark around the cluster. We first test-and reject-a series of system-specific simple constraints that might limit full host exploitation, such as asynchronous maturation of host eggs. We then consider classical hypotheses for the evolution of restraint. Prudent predation and bet-hedging fail as explanations because the wasp lives as a large, well-mixed population. Additionally, we find no individual benefits to the parasitoid of developing in a sparsely parasitized host nest. However, an optimal foragingmodel, including empirically measured costs of superparasitism and hyperparasitism, can explain through individual selection both the consistently low rate of parasitism and deterrent marking. [ABSTRACT FROM AUTHOR]