Abstract
In species with a high degree of fission-fusion social dynamics, fusions may trigger social conflict and thus provide an opportunity to identify sources of social tension and mechanisms related to its alleviation. We characterized behavioral and endocrine responses of captive female bonobos (Pan paniscus) to fusions within a zoo facility designed to simulate naturalistic fission-fusion social dynamics. We compared urinary cortisol levels and frequencies of aggression, grooming and socio-sexual interactions between female bonobos while in stable sub-groups and when one “joiner” was reunited with the “residents” of another sub-group. We hypothesized that fusions would trigger increases in aggression and cortisol levels among reunited joiners and resident females. We further predicted that females who face more uncertainty in their social interactions following fusions may use grooming and/or socio-sexual behavior to reduce social tension and aggression. The only aggression on reunion days occurred between reunited females, but frequencies of aggression remained low across non-reunion and reunion days, and there was no effect of fusions on cortisol levels. Fusions did not influence patterns of grooming, but there were increases in socio-sexual solicitations and socio-sexual interactions between joiners and resident females. Joiners who had been separated from residents for longer received the most solicitations, but were also more selective in their acceptance of solicitations and preferred to have socio-sexual interactions with higher-ranking residents. Our results suggest that socio-sexual interactions play a role in reintegrating female bonobos into social groups following fusions. In addition, females who receive a high number of solicitations are able to gain more control over their socio-sexual interactions and may use socio-sexual interactions for other purposes, such as to enhance their social standing.
Highlights
In contrast with the majority of primate species, bonobos (Pan paniscus) live in patrilineal social groups characterized by male life-long residency and female dispersal at sexual maturity, typically into groups without other relatives present [1]
Since we found no effect of observation day on cortisol levels, we included samples from focal females on non-reunion days (N = 27 samples) and reunion days (N = 30 samples), to increase the sample size for each focal female
In several species with frequent fluctuations in the size, composition and spatial cohesion of sub-groups, ritualized social interactions are common during fusions, including embraces among spider monkeys [22] and chimpanzees [24] and pseudo-penile displays among female hyenas [17], [48]
Summary
In contrast with the majority of primate species, bonobos (Pan paniscus) live in patrilineal social groups characterized by male life-long residency and female dispersal at sexual maturity, typically into groups without other relatives present [1]. Other primate species with a bias towards male philopatry and female dispersal include the closely related chimpanzee (Pan troglodytes sp.), spider monkeys (Ateles sp.) and ancestral and modern humans [2], [3]. Welcome Back: Responses of Female Bonobos to Fusions design, data collection and analysis, decision to publish, or preparation of the manuscript
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