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Highly differentiated and affiliative social relationships are observed in a variety of mammals, including primates, cetaceans, and social carnivores. Although there has been a transformation in our understanding of the form and function of social bonds in the past two decades, the role of early life social experiences in the development of bonds remains less clear. Few studies have examined whether social relationships during infancy and juvenility (aside from those between mothers and offspring) persist into adulthood. In this study, we used longitudinal data on wild chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania, to investigate the effects of party-level association during infancy and juvenility (hereafter immaturity) on affiliative relationships among adult males (the philopatric sex). In total, we examined behavioral data from focal follows between 1970 and 2015 (N = 23 adult males). We used maternal associations as proxies for the associations of immature males, and we measured adult male social relationships using party-level associations and grooming activity. We found that immature males that associated with individual adult males at higher rates had stronger relationships with those same adult males later in life. By contrast, rates of association between pairs of immature males did not predict the strength of their dyadic relationships as adults. Overall, these findings emphasize the importance of early socialization in male chimpanzee social development. These results also reinforce studies in mountain gorillas (Gorilla beringei) and bottlenose dolphins (Tursiops sp.), suggesting that the persistence of social relationships that do not involve the mother may be more likely to evolve in long-lived species where young adult males face challenges entering an adult hierarchy composed of stronger and/or more socially experienced competitors. [ABSTRACT FROM AUTHOR]

Establishing the order of a dominance hierarchy among female chimpanzees ( Pan troglodytes) is complicated by the fact that they often forage solitarily, and aggressive interactions between them occur infrequently. Authors of previous studies have typically ranked females via the direction of submissive pant-grunts and the outcome of agonistic interactions. Given that higher rank correlates with higher reproductive success in female chimpanzees, assessing rank is important but may be limited by sparsely populated dominance matrices. I tested the hypothesis that rank predicts the direction of female approaches. There is a significant relationship among Gombe females between the frequency with which a female was approached and her dominance rank. Dominant females approached other females less often than they were approached. Though approached frequencies failed to meet the criteria for formal rank indicators, they may be useful as real indicators of subordination. Because approach interactions occur far more frequently than pant-grunts, they may be useful in assigning categorical rank when traditional dominance metrics are limited. [ABSTRACT FROM AUTHOR]

Researchers have reported a total of 31 infanticides in 4 different chimpanzee (Pan troglodytes) populations. Though infanticide is infrequent, low reproductive rates of females likely make it a strong selective pressure in the species. We report a new incident of intragroup infanticide in Gombe National Park, Tanzania, in which a community male attacked a 3.5-yr-old male. We then consider the infanticide in terms of adaptive and nonadaptive explanations for infanticide including the social pathology, by-product of male aggression, nutritive benefits, resource competition, and sexual selection hypotheses. The incident reported here is not well explained by any of them. While the infanticide is puzzling in terms of ultimate explanations for infanticide, it provides a good context in which to consider proximate mechanisms for offspring recognition. The incident provides some evidence that males may use their mating history with the mother to assess paternity likelihood. [ABSTRACT FROM AUTHOR]