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In eusocial insects, the ability to discriminate nest-mates from non-nest-mates is widespread and ensures that altruistic actions are directed towards kin and agonistic actions are directed towards non-relatives. Most tests of nest-mate recognition have focused on hymenopterans, and suggest that cooperation typically evolves in tandem with strong antagonism towards non-nest-mates. Here, we present evidence from a phylogenetically and behaviourally basal termite species that workers discriminate members of foreign colonies. However, contrary to our expectations, foreign intruders were the recipients of more rather than less cooperative behaviour and were not subjected to elevated aggression. We suggest that relationships between groups may be much more peaceable in basal termites compared with eusocial hymenoptera, owing to energetic and temporal constraints on colony growth, and the reduced incentive that totipotent workers (who may inherit breeding status) have to contribute to self-sacrificial intergroup conflict.

War, in human and animal societies, can be extremely costly but can also offer significant benefits to the victorious group. We might expect groups to go into battle when the potential benefits of victory (V) outweigh the costs of escalated conflict (C); however, V and C are unlikely to be distributed evenly in heterogeneous groups. For example, some leaders who make the decision to go to war may monopolize the benefits at little cost to themselves ('exploitative' leaders). By contrast, other leaders may willingly pay increased costs, above and beyond their share of V ('heroic' leaders). We investigated conflict initiation and conflict participation in an ecological model where single-leader–multiple-follower groups came into conflict over natural resources. We found that small group size, low migration rate and frequent interaction between groups increased intergroup competition and the evolution of 'exploitative' leadership, while converse patterns favoured increased intragroup competition and the emergence of 'heroic' leaders. We also found evidence of an alternative leader/follower 'shared effort' outcome. Parameters that favoured high contributing 'heroic' leaders, and low contributing followers, facilitated transitions to more peaceful outcomes. We outline and discuss the key testable predictions of our model for empiricists studying intergroup conflict in humans and animals. This article is part of the theme issue 'Intergroup conflict across taxa'. [ABSTRACT FROM AUTHOR]

Personality traits, such as the propensity to cooperate, are often inherited from parents to offspring, but the pathway of inheritance is unclear. Traits could be inherited via genetic or parental effects, or culturally via social learning from role models. However, these pathways are difficult to disentangle in natural systems as parents are usually the source of all of these effects. Here, we exploit natural 'cross fostering' in wild banded mongooses to investigate the inheritance of cooperative behaviour. Our analysis of 800 adult helpers over 21 years showed low but significant genetic heritability of cooperative personalities in males but not females. Cross fostering revealed little evidence of cultural heritability: offspring reared by particularly cooperative helpers did not become more cooperative themselves. Our results demonstrate that cooperative personalities are not always highly heritable in wild, and that the basis of behavioural traits can vary within a species (here, by sex). [ABSTRACT FROM AUTHOR]

Mounting evidence suggests that patterns of local relatedness can change over time in predictable ways, a process termed kinship dynamics. Kinship dynamics may occur at the level of the population or social group, where the mean relatedness across all members of the population or group changes over time, or at the level of the individual, where an individual's relatedness to its local group changes with age. Kinship dynamics are likely to have fundamental consequences for the evolution of social behaviour and life history because they alter the inclusive fitness payoffs to actions taken at different points in time. For instance, growing evidence suggests that individual kinship dynamics have shaped the evolution of menopause and age-specific patterns of helping and harming. To date, however, the consequences of kinship dynamics for social evolution have not been widely explored. Here we review the patterns of kinship dynamics that can occur in natural populations and highlight how taking a kinship dynamics approach has yielded new insights into behaviour and life-history evolution. We discuss areas where analysing kinship dynamics could provide new insight into social evolution, and we outline some of the challenges in predicting and quantifying kinship dynamics in natural populations. [ABSTRACT FROM AUTHOR]

Cooperation in nature is ubiquitous, but is susceptible to social cheats who pay little or no cost of cooperation yet reap the benefits. The effect such cheats have on reducing population productivity suggests that there is selection for cooperators to mitigate the adverse effects of cheats. While mechanisms have been elucidated for scenarios involving a direct association between producer and cooperative product, it is less clear how cooperators may suppress cheating in an anonymous public goods scenario, where cheats cannot be directly identified. Here, we investigate the real-time evolutionary response of cooperators to cheats when cooperation is mediated by a diffusible public good: the production of iron-scavenging siderophores by Pseudomonas aeruginosa. We find that siderophore producers evolved in the presence of a high frequency of non-producing cheats were fitter in the presence of cheats, at no obvious cost to population productivity. A novel morphotype independently evolved and reached higher frequencies in cheat-adapted versus control populations, exhibiting reduced siderophore production but increased production of pyocyanin-an extracellular toxin that can also increase the availability of soluble iron. This suggests that cooperators may have mitigated the negative effects of cheats by downregulating siderophore production and upregulating an alternative iron-acquisition public good. More generally, the study emphasizes that cooperating organisms can rapidly adapt to the presence of anonymous cheats without necessarily incurring fitness costs in the environment they evolve in. [ABSTRACT FROM AUTHOR]

In his famous haplodiploidy hypothesis, W. D. Hamilton proposed that high sister–sister relatedness facilitates the evolution of kin-selected reproductive altruism among Hymenopteran females. Subsequent analyses, however, suggested that haplodiploidy cannot promote altruism unless altruists capitalize on relatedness asymmetries by helping to raise offspring whose sex ratio is more female-biased than the population at large. Here, we show that haplodiploidy is in fact more favourable than is diploidy to the evolution of reproductive altruism on the part of females, provided only that dispersal is male-biased (no sex-ratio bias or active kin discrimination is required). The effect is strong, and applies to the evolution both of sterile female helpers and of helping among breeding females. Moreover, a review of existing data suggests that female philopatry and non-local mating are widespread among nest-building Hymenoptera. We thus conclude that Hamilton was correct in his claim that ‘family relationships in the Hymenoptera are potentially very favourable to the evolution of reproductive altruism’. [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]

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]

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]

Conflict between groups is a notable feature of many animal societies. Recent theoretical models suggest that violent intergroup conflict can shape patterns of within-group cooperation. However, despite its prevalence in social species, the adaptive significance of violent intergroup conflict has been little explored outside of humans and chimpanzees, Pan troglodytes . A barrier to current understanding of the role of intergroup conflict in the evolution of social behaviour is a lack of information on the causes and consequences of aggression between groups. Here, we examined the causes and fitness consequences of intergroup conflict in the banded mongoose, Mungos mungo , using a 16-year data set of observed intergroup interactions, life history and behaviour. Banded mongooses are cooperative breeders that live in highly territorial groups and engage in frequent, aggressive and violent intergroup interactions. We found that intensified population-wide competition for food and mates increased the probability of intergroup interactions, and that increased intergroup conflict was associated with periods in which groups were growing in size. Intergroup conflict had fitness costs in terms of reduced litter and adult survival but no cost to pregnant females: in fact, females were less likely to abort following an intergroup interaction than when there had been no recent intergroup conflict. Our results suggest that intergroup conflict has measurable costs to both individuals and groups in the long and short term, and that levels of conflict among groups could be high enough to affect patterns of within-group cooperative behaviour. Establishing the consequences of intergroup conflict in cooperative species can shed light on patterns of conflict and cooperation within groups and, in turn, facilitate our understanding of social evolution. [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]

In cooperatively breeding vertebrate societies, contributions to offspring care can vary greatly between group members. Kin selection theory predicts that cooperation will be favoured when directed towards relatives and when the cost to benefit ratio is low. The fitness costs of helping in turn depend on the impact of energetic investments in care on future reproductive success, which is likely to vary between helpers. For example, investments may impact more on a young helper, which needs to invest energy in growth and is an inexperienced forager. We investigated how a key predictor of cost, food availability (estimated using rainfall), influences helping behaviour in the banded mongoose, Mungos mungo. In this cooperative carnivore, a variable number of group members breed while almost all help to rear the communal litter. Nonbreeding females and juvenile males helped less when food was scarce, reflecting the potentially high costs of weight loss and reduced growth on survival and future reproductive success. In contrast, adult males maintained their investment in care as food supply decreased, probably because body condition has relatively little impact on male reproductive success in this species. Breeding females (with pups in the communal litter) also maintained their helping effort as food supply decreased. Although mothers invested highly in care, there was no evidence that they preferentially cared for their own pups, probably because synchronized birthing scrambles maternity cues. Patterns of care in the banded mongoose thus seem to reflect the benefits gained from helping and the long-term fitness costs to the helper. [Copyright &y& Elsevier]