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Examining the ontogeny of conflict-mitigating behaviours in our closest living relatives is an important component of understanding the evolutionary origins of cooperation in our species. In this study, we used 26 years of data to investigate the emergence of third-party affiliation (TPA), defined as affiliative contact given to recipients of aggression by uninvolved bystanders (regardless of initiation), in wild immature eastern chimpanzees (Pan troglodytes schweinfurthii) of Gombe National Park, Tanzania. We also characterized TPA by mothers in the same dataset as an adult benchmark for interpreting immature TPA patterns. In summary, we found that immatures did not express TPA as measured by grooming between the ages of 1.5 and 12.0 years, and that there was limited evidence that immatures expressed TPA via play. We also found that mothers did express TPA to offspring, although mothers did not show TPA towards non-offspring. Cases of TPA by mothers to other adults were too few to analyse separately. These results contrast with findings from captive studies which found that chimpanzees as young as 6 years of age demonstrated TPA. We argue that within-species variation in the expression of TPA, both in immatures and adulthood, provides evidence that the conflict management behaviours of young chimpanzees may be heavily influenced by social, ecological and demographic factors.

Monitoring adrenocortical activity in wild primate populations is critical, given the well-documented relationship between stress, health, and reproduction. Although many primate studies have quantified fecal glucocorticoid metabolite ( FGM) concentrations, it is imperative that researchers validate their method for each species. Here, we describe and validate a technique for field extraction and storage of FGMs in wild chimpanzees ( P an troglodytes). Our method circumvents many of the logistical challenges associated with field studies while yielding similar results to a commonly used laboratory method. We further validate that our method accurately reflects stress physiology using an adrenocorticotropic hormone challenge in a captive chimpanzee and an FGM peak at parturition in a wild subject. Finally, we quantify circadian patterns for FGMs for the first time in this species. Understanding these patterns may allow researchers to directly link specific events with the stress response. Am. J. Primatol. 75:57-64, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Competition for fertile females determines male reproductive success in many species. The priority of access model predicts that male dominance rank determines access to females, but this model has been difficult to test in wild populations, particularly in promiscuous mating systems. Tests of the model have produced variable results, probably because of the differing socioecological circumstances of individual species and populations. We tested the predictions of the priority of access model in the chimpanzees of Gombe National Park, Tanzania. Chimpanzees are an interesting species in which to test the model because of their fission–fusion grouping patterns, promiscuous mating system and alternative male mating strategies. We determined paternity for 34 offspring over a 22-year period and found that the priority of access model was generally predictive of male reproductive success. However, we found that younger males had higher success per male than older males, and low-ranking males sired more offspring than predicted. Low-ranking males sired offspring with younger, less desirable females and by engaging in consortships more often than high-ranking fathers. Although alpha males never sired offspring with related females, inbreeding avoidance of high-ranking male relatives did not completely explain the success of low-ranking males. While our work confirms that male rank typically predicts male chimpanzee reproductive success, other factors are also important; mate choice and alternative male strategies can give low-ranking males access to females more often than would be predicted by the model. Furthermore, the success of younger males suggests that they are more successful in sperm competition. [Copyright &y& Elsevier]

Studies from many different taxa have demonstrated that dominance rank greatly influences individual space use. While the importance of dominance among female chimpanzees, Pan troglodytes, was debated in the past, mounting evidence now shows that rank is very important. In particular, rank has been shown to influence body mass, foraging strategies, association patterns, and ultimately, reproductive success. In this study, we investigated how rank influenced female space use among chimpanzees, P.t. schweinfurthii, at Gombe National Park, Tanzania. Analysing 10 years of data, we found that new immigrants used areas away from dominant females, and that subordinates had lower site fidelity. We also found that high-ranking females had smaller core areas and that this size difference was pronounced during periods of food scarcity when food competition is highest. These patterns suggest that dominant females outcompete subordinates, forcing them to settle elsewhere, range more widely, and shift their space use across time. [Copyright &y& Elsevier]

A large body of literature demonstrates the adaptive benefits of social relationships between kin, including fitness and survival. Given that most social mammals are characterized by male-biased dispersal, the majority of research on kin selection and associated advantages focuses on social relationships between female kin. Meanwhile, research on social relationships between adult male and female kin has primarily focused on inbreeding avoidance or the benefit to adult sons, with less attention on potential advantages these social relationships may provide females. The general pattern of male dominance over females in most mammal species suggests that females may benefit from protective associations with adult male kin. Using 43 years of behavioural data on the wild chimpanzees, Pan troglodytes schweinfurthii , of Gombe National Park, Tanzania, we examined association patterns between females and their adult maternal male kin. We specifically focused on how these associations may represent a trade-off between inbreeding avoidance and protection for females, particularly against infanticide. In accordance with inbreeding avoidance, we predicted that females' association with adult kin would decrease when they were maximally tumescent, signalling sexual receptivity. To determine whether female–male kin associations provide protection to females, we examined female associations with adult male kin during their first year postpartum when infants are most vulnerable to infanticide. We predicted that during this first year postpartum, females would have a higher association with male kin than with unrelated males. We found that females associated more with adult sons and brothers than with unrelated males when they did not have a sexual swelling. Female association increased with all males across tumescence but females associated less with their brothers than they did with their sons and unrelated males when they were maximally tumescent, providing equivocal support for the inbreeding avoidance hypothesis. Furthermore, females associated more with both sons and brothers than with unrelated males in the first 6 months of the postpartum period. Higher association with brothers, relative to unrelated males, persisted throughout the first year postpartum. Together, these results speak to the cost–benefit trade-off in female and adult male kin associations, highlighting the potential protective advantage for females, especially during the postpartum period. • We examined association patterns between females and their adult maternal male kin. • Association with sons, brothers and unrelated males increased with swelling size. • Association with sons was higher than with other males during early postpartum. • Association with brothers was higher than with unrelated males 1 year postpartum. • Our results suggest a potential male kin protective advantage postpartum. [ABSTRACT FROM AUTHOR]

Sex differences in the behaviour of human children are a hotly debated and often controversial topic. However, several recent studies have documented a biological basis to key aspects of child social behaviour. To further explore the evolutionary basis of such differences, we investigated sex differences in sociability in wild chimpanzee, Pan troglodytes schweinfurthii, infants at Gombe National Park, Tanzania. We used a long-term data set on mother–infant behaviour to analyse the diversity of infant chimpanzee social partners from age 30 to 36 months. Male infants (N =12) interacted with significantly more individuals than female infants did (N =8), even when maternal sociability was controlled for. Furthermore, male infants interacted with significantly more adult males than female infants did. Our data indicate that the well-documented sex differences in adult chimpanzee social tendencies begin to appear quite early in development. Furthermore, these data suggest that the behavioural sex differences of human children are fundamentally rooted in our biological and evolutionary heritage. [ABSTRACT FROM AUTHOR]

Given the deleterious consequences associated with chronic stress, individual differences in stress susceptibility can have important fitness implications. These differences may be explained in part by dominance status because high rank is typically associated with decreased aggression and improved nutrition. Here, we examined the relationship between dominance and social stress in lactating chimpanzees, Pan troglodytes schweinfurthii, at Gombe National Park, Tanzania. We did so by pairing daily demographic and behavioural data with faecal glucocorticoid metabolite (FGM) concentrations collected over 37 months. While there was no main effect of rank, interesting differences emerged by adult subgroup size and adult sex ratio (males/females). We found that differences in FGM concentrations between high- and low-ranking females were most pronounced as adult subgroup size and sex ratio increased. Low-ranking females had higher FGM concentrations in larger subgroups and in subgroups biased towards adult males; we observed no comparable change in FGM concentrations amongst high-ranking females. Because low-ranking females were the recipient of significantly more male aggression relative to females of high rank, these patterns may be driven by psychosocial stress in low-ranking females. There was no significant change in diet quality across subgroup sizes; this finding suggests that nutritional stressors were not driving differences in female FGM concentrations. Being susceptible to social stress has important fitness implications as it may constrain low-ranking females from ‘choosing’ optimal subgroups to take advantage of food resources and/or for the socialization of their offspring. [Copyright &y& Elsevier]

Female space use can have important fitness consequences, which are likely due to differential access to food resources. Many studies have explored spatial competition in solitary species, but little is known about how individuals in social species compete over shared space. In this study, we investigate spatial patterns of aggression among female East African chimpanzees, Pan troglodytes schweinfurthii. This species provides an excellent opportunity to study spatial competition since (1) female chimpanzees occupy overlapping core areas (small areas of the community range in which individuals concentrate their space use) and (2) female core area quality is correlated with reproductive success, suggesting that females compete over long-term access to core areas. Here, we examine how female aggression towards other females varies inside and outside individual female core areas during a 14-year period at Gombe National Park, Tanzania. Overall, females showed higher rates of aggression inside than outside their own core areas. This pattern was driven by spatial variation in aggression in nonfeeding contexts. While food-related aggression did not vary spatially, females were more aggressive in nonfeeding contexts inside their core areas than they were outside their core areas. These results suggest that female chimpanzees follow a mixed strategy in which they compete for long-term access to resources in their core areas as well as for immediate access to food throughout the community range. [Copyright &y& Elsevier]