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Ecological conditions are expected to have an important influence on individuals' investment in cooperative care. However, the nature of their effects is unclear: both favorable and unfavorable conditions have been found to promote helping behavior. Recent studies provide a possible explanation for these conflicting results by suggesting that increased ecological variability, rather than changes in mean conditions, promote cooperative care. However, no study has tested whether increased ecological variability promotes individual- level helping behavior or the mechanisms involved. We test this hypothesis in a long-term study population of the cooperatively breeding banded mongoose, Mungos mungo, using 14 years of behavioral and meteorological data to explore how the mean and variability of ecological conditions influence individual behavior, body condition, and survival. Female body condition was more sensitive to changes in rainfall leading to poorer female survival and pronounced male-biased group compositions after periods of high rainfall variability. After such periods, older males invested more in helping behavior, potentially because they had fewer mating opportunities. These results provide the first empirical evidence for increased individual helping effort in more variable ecological conditions and suggest this arises because of individual differences in the effect of ecological conditions on body condition and survival, and the knock-on effect on social group composition. Individual differences in sensitivity to environmental variability, and the impacts this has on the internal structure and composition of animal groups, can exert a strong influence on the evolution and maintenance of social behaviors, such as cooperative care. [ABSTRACT FROM AUTHOR]

Paper wasps negotiate over help using indicators of demand. Animal societies are composed of individuals whose genetic interests are often opposed. We conducted experiments on a cooperative paper wasp which reveal the behavioural rules by which group members settle these conflicts.Recent theory and empirical studies of avian biparental systems suggest that animals resolve conflict over parental care via a process of behavioral negotiation or “rules for responding.” Less is known, however, about whether negotiation over helping effort occurs in cooperatively breeding animal societies or whether behavioral negotiation requires a relatively large brain. In this study, we tested whether negotiation over help occurs in a social insect, the paper wasp Polistes dominulus, by recording individual responses to both observed and experimentally induced foraging returns by other group members. In our experiments, we manipulated food delivery to the nest in 2 ways: 1) by catching departing foragers and giving them larval food to take back to the nest and 2) by giving larval food directly to wasps on the nest, which they then fed to larvae, so increasing food delivery independently of helper effort. We found no evidence from Experiment 1 that helpers adjusted their own foraging effort according to the foraging effort of other group members. However, when food was provided directly to the nest, wasps did respond by reducing their own foraging effort. One interpretation of this result is that paper wasp helpers adjust their helping effort according to the level of offspring need rather than the work rate of other helpers. Negotiation based on indicators of demand rather than work rate is a likely mechanism to resolve conflict over investment in teams where helpers cannot observe each other’s work rate directly, as is commonly the case in insect and vertebrate societies. [ABSTRACT FROM PUBLISHER]

The ability to individually recognize conspecifics is acknowledged as one of the prerequisites for the development of sophisticated social relationships in group-living species. It has been hypothesized that the discrimination of individual identities is crucial for the maintenance of social relationships and cooperation based on repeated interactions, and for the evolution of many social behaviours. Previous studies have shown that the close calls of the cooperatively breeding banded mongoose Mungos mungo are individually distinct. For instance, banded mongoose pups are able to distinguish between close calls of their escort and of a non-escort. In this study, we used playbacks based on the recently proposed violation-of-expectation paradigm and a dominance/age class recognition setup to investigate whether adult banded mongooses use the individual signature of close calls to distinguish among adult group members. We found no evidence that the individual signature in close calls is used to discriminate identity in banded mongooses. Based on the previous work, we suggest that this is not because banded mongooses are incapable of using signatures as a means of individual discrimination, but because the benefits of such discrimination are low. The study highlights the importance of understanding the function of a signal (e.g. the expected response), timing and the biology of the species when designing and performing playback experiments. [ABSTRACT FROM AUTHOR]

Social species show considerable variation in the extent to which dominant females suppress subordinate reproduction. Much of this variation may be influenced by the cost of active suppression to dominants, who may be selected to balance the need to maximize the resources available for their own offspring against the costs of interfering with subordinate reproduction. To date, the cost of reproductive suppression has received little attention, despite its potential to influence the outcome of conflict over the distribution of reproduction in social species. Here, we investigate possible costs of reproductive suppression in banded mongooses, where dominant females evict subordinates from their groups, thereby inducing subordinate abortion. We show that evicting subordinate females is associated with substantial costs to dominant females: pups born to females who evicted subordinates while pregnant were lighter than those born after undisturbed gestations; pups whose dependent period was disrupted by an eviction attained a lower weight at independence; and the proportion of a litter that survived to independence was reduced if there was an eviction during the dependent period. To our knowledge, this is the first empirical study indicating a possible cost to dominants in attempting to suppress subordinate breeding, and we argue that much of the variation in reproductive skew both within and between social species may be influenced by adaptive variation in the effort invested in suppression by dominants. [ABSTRACT FROM AUTHOR]

In human societies, social behaviour is strongly influenced by threats of punishment, even though the threats themselves rarely need to be exercised. Recent experimental evidence suggests that similar hidden threats can promote cooperation and limit within-group selfishness in some animal systems. In other animals, however, threats appear to be ineffective. Here I review theoretical and empirical studies that help to understand the evolutionary causes of these contrasting patterns, and identify three factors--impact, accuracy and perception--that together determine the effectiveness of threats to induce cooperation. [ABSTRACT FROM AUTHOR]

Summary: Evidence has accumulated in recent years indicating that traditions are not a unique feature of human societies but may be common in primates and some other mammals []. However, most documented cases remain contentious because observational studies of free-living animals suffer from interpretive weaknesses [], whereas social diffusion experiments performed in captivity (e.g., []) may not reflect conditions found in nature []. Here we use experiments under natural conditions to demonstrate that wild banded mongooses (Mungos mungo) pass preferences for one of two possible foraging techniques on to the next generation through contextual imitation. Notably, both techniques coexisted within the same groups and were transmitted concurrently between adults and pups, which form close one-to-one associations during the period of pup dependency. This experimental demonstration of a foraging tradition in wild mammals provides critical evidence to support previous accounts of traditions in nonhuman animals based on distribution patterns of natural behaviors []. Moreover, our data provide the first experimental demonstration of imitation in wild mammals and, contrary to common assumption [], show that social learning need not lead to an increased behavioral homogeneity within groups. [Copyright &y& Elsevier]

Most examples of cooperation in nature share a common feature: individuals can interact to produce a productivity benefit or fitness surplus, but there is conflict over how these gains are shared. A central question is how threats to exercise outside options influence the resolution of conflict within such cooperative associations. Here we show how a simple principle from economic bargaining theory, the outside option principle, can help to solve this problem in biological systems. According to this principle, outside options will affect the resolution of conflict only when the payoff of taking up these options exceeds the payoffs individuals can obtain from bargaining or negotiating within the group; otherwise, threats to exercise outside options are not credible and are therefore irrelevant. We show that previous attempts to incorporate outside options in synthetic models of reproductive conflict fail to distinguish between credible and incredible threats, and then we use the outside option principle to develop credible synthetic models in two contexts: reproductive skew and biparental care. A striking prediction of our analysis is that outside options are least relevant to the resolution of conflict in cooperative groups of kin and are most relevant in transient associations or interactions among nonrelatives. Our analysis shows a way to link the resolution of within-group conflict to the environmental setting in which it occurs, and it illuminates the role of threats in the evolution of social behavior. [ABSTRACT FROM AUTHOR]

Recent studies of reproductive skew have revealed great variation in the distribution of direct fitness among group members, yet there have been surprisingly few attempts to explore the consequences of such variation for stable group size, and none that take into account the future benefits of group membership to nonbreeders. This means that the existing theory is not suited to explain the group size of most cooperatively breeding vertebrates and primitively social insects in which group membership involves substantial future benefits. Here we model the group size of such species as social queues in which nonbreeders can inherit a breeding position if they outlive those ahead of them in the queue. We demonstrate, however, that the results can be generalized to systems in which inheritance occurs via scramble competition, rather than via a strict queue. The model predicts that stable group size will depend on the number of breeding positions in the group and the mortality rates of breeders and nonbreeders, but not on the distribution of reproduction among the pool of breeders. This is because deaths occur at random, so that each individual has the same chance of surviving to reach each breeding position. We tested a specific prediction of the model using data on ovarian development in the paper wasp, Polistes dominulus. We found a positive correlation between group size and the proportion of females with fully developed eggs, as predicted. Our results clarify the interaction between the dominance structure and size of animal groups and add to the growing recognition of the potential for inheritance as a major determinant of both individual behavior and group-level characteristics of animal societies. [ABSTRACT FROM AUTHOR]

Recent theory suggests that much of the wide variation in individual behavior that exists within cooperative animal societies can be explained by variation in the future direct component of fitness, or the probability of inheritance. Here we develop two models to explore the effect of variation in future fitness on social aggression. The models predict that rates of aggression will be highest toward the front of the queue to inherit and will be higher in larger, more productive groups. A third prediction is that, in seasonal animals, aggression will increase as the time available to inherit the breeding position runs out. We tested these predictions using a model social species, the paper wasp Polistes dominulus. We found that rates of both aggressive ‘displays’ (aimed at individuals of lower rank) and aggressive ‘tests’ (aimed at individuals of higher rank) decreased down the hierarchy, as predicted by our models. The only other significant factor affecting aggression rates was date, with more aggression observed later in the season, also as predicted. Variation in future fitness due to inheritance rank is the hidden factor accounting for much of the variation in aggressiveness among apparently equivalent individuals in this species. [ABSTRACT FROM AUTHOR]

Low-level social aggression is a conspicuous feature of cooperative animal societies, but its precise function is usually unclear. One long-standing hypothesis is that aggressive displays by dominant individuals serve to reduce uncertainty about relative strength and deter subordinates from starting fights that they are unlikely to win. However, most formal theoretical models of this idea do not consider how the credibility of deterrent signals might change over time in social groups. We developed a simple model of dominant aggression as a deterrent signal, which takes into account how credibility changes over time and how selection should act on receiver memory. We then carried out an experimental test of the predictions of our model on a field population of the paper wasp, Polistes dominulus. The match between our theoretical and empirical results suggests that low-level social aggression can help to maintain the stability and productivity of cooperative associations in this species. Moreover, our work suggests that rates of aggression in animal societies and the robustness of social memories are likely to be intimately related.Social animals often spend a great deal of time and energy being aggressive to one another, for reasons that are not clear. Our experiment on paper wasps shows that aggression can in fact promote peace and harmony in cooperative groups. [ABSTRACT FROM PUBLISHER]

Reproductive skew theory provides a compelling explanation for the partitioning of reproduction among individuals within animal societies. One constructive criticism of the theory is that there are too many models, all of which have different assumptions and predictions, which makes it difficult to know what to test. Here we begin the process of tackling this problem, by re-examining the assumptions and predictions of basic concession and restraint models, two transactional models that are often tested as alternatives. Concession models assume that the dominant has complete control over the allocation of reproduction but may yield some of the group''s reproduction to prevent the subordinate from voluntarily departing. Restraint models assume that the subordinate has complete control over the allocation of reproduction but may not claim all of the group''s reproduction to prevent the dominant from forcibly evicting it. We show that the group dissolution tactics that individuals use (forcible eviction or voluntary departure) need not be an assumption of the model, but rather they can be predicted using Hamilton''s rule and the standard variables of skew models. We reveal that the assumption that one individual (dominant or subordinate) has complete control over the allocation of reproduction is an idea common to both models, and we resolve this semantic difference by calling this individual ‘the allocator’. We show that, regardless of the group dissolution tactics that individuals adopt, the allocator''s share of the reproduction always increases as relatedness increases, as group productivity increases, and as constraints on leaving to breed elsewhere intensify. We conclude that concession and restraint type models make qualitatively similar predictions, and should not be tested as alternatives. In summary, this study makes the transactional framework of reproductive skew more general, by eliminating restrictive assumptions, and more amenable to testing in the field, by clarifying assumptions and predictions. [Copyright &y& Elsevier]

In animal societies, conflict within groups can result in eviction, where individuals are often permanently expelled from their group. To understand the evolution of eviction and its role in the resolution of within-group conflict requires information on the demographic consequences of eviction for individuals and groups. However, such information is usually difficult to obtain because of the difficulty in tracking and monitoring individuals after they are evicted from their natal groups. Here we used a 15-year data set on life history and demography to investigate the consequences of eviction in a tractable cooperatively breeding mammal, the banded mongoose, Mungos mungo . In this species, groups of individuals are periodically evicted en masse and eviction is a primary mechanism by which new groups form in the study population. Following eviction, we found sex differences in dispersal distance: some females established new groups on the study peninsula but males always dispersed away from the study peninsula. Evicted females suffered reduced reproductive success in the year after eviction. For the evicting group, eviction was associated with increased per capita reproductive success for females, suggesting that eviction is successful in reducing reproductive competition. However, eviction was also associated with increased intergroup conflict for the evicting group. Our results suggest that within-group conflict resolution strategies affect group productivity, group interactions and the structure of the population, and hence have fitness impacts that reach beyond the individual evictors and evictees involved in eviction. [ABSTRACT FROM AUTHOR]

Individual differences in contributions to cooperation can be strikingly consistent over time giving rise to alternative cooperative phenotypes within animal societies. Following the social niche specialization hypothesis, these consistent differences may be driven by social conflict over reproductive opportunities if individuals specializing as ‘breeders’ and ‘nonbreeders’ experience a beneficial reduction in social conflict and differential costs associated with cooperating. This hypothesis gives three testable predictions: (1) consistent individual differences in cooperative behaviour will be accompanied by consistent individual differences in reproductive behaviour, (2) individuals contributing heavily to reproduction will contribute relatively little to cooperative behaviours within the same breeding attempt and vice versa, and (3) individuals that consistently contribute heavily to reproduction over their lifetime will also consistently contribute less to cooperative behaviours and vice versa. We tested these predictions with a 15-year investigation into the lifetime patterns of mate guarding and two forms of cooperative offspring care (‘babysitting’ and ‘escorting’) in a wild population of banded mongooses. We found significant repeatability of individual contributions to both cooperative behaviours, as well as significant repeatability of individual levels of mate guarding. However, we found no evidence of negative covariance between contributions to cooperative and reproductive behaviours either within breeding attempts or across lifetimes. This suggests that the observed consistent individual differences in both cooperative behaviour and reproduction are not associated; there is no evidence of a trade-off between reproduction and cooperation. However, we found a significant positive covariance between babysitting and escorting when estimated both within breeding attempts and across lifetimes, which suggests that some group members are generally more cooperative than others, contributing more to both behaviours over their lifetimes. The drivers of this consistent individual variation in contributions to cooperation remain unknown. [ABSTRACT FROM AUTHOR]