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R Soc Open Sci. 2017 May 3;4(5):161081. doi: 10.1098/rsos.161081. eCollection 2017 May.

Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation.

Author information

1
Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
2
Liverpool John Moores University, Faculty of Science, Natural Sciences and Psychology, Liverpool, UK.
3
Centre for Research and Conservation, Royal Zoological Society of Antwerp, Antwerp, Belgium.
4
School of Human Evolution & Social Change, Arizona State University, Tempe, AZ, USA.
5
Institute for Human Origins, Arizona State University, Tempe, AZ, USA.
6
Budongo Conservation Field Station, Masindi, Uganda.
7
Cognitive Science Centre, University of Neuchâtel, Neuenburg, Switzerland.
8
Taï Chimpanzee Project, Centre Suisse de Recherches Scientifiques, BP 1303 Abidjan 01, Côte d'Ivoire.
9
Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.

Abstract

In several group-living species, individuals' social preferences are thought to be influenced by cooperation. For some societies with fission-fusion dynamics, sex-specific association patterns reflect sex differences in cooperation in within- and between-group contexts. In our study, we investigated this hypothesis further by comparing sex-specific association patterns in two closely related species, chimpanzees and bonobos, which differ in the level of between-group competition and in the degree to which sex and kinship influence dyadic cooperation. Here, we used long-term party composition data collected on five chimpanzee and two bonobo communities and assessed, for each individual of 10 years and older, the sex of its top associate and of all conspecifics with whom it associated more frequently than expected by chance. We found clear species differences in association patterns. While in all chimpanzee communities males and females associated more with same-sex partners, in bonobos males and females tended to associate preferentially with females, but the female association preference for other females is lower than in chimpanzees. Our results also show that, for bonobos (but not for chimpanzees), association patterns were predominantly driven by mother-offspring relationships. These species differences in association patterns reflect the high levels of male-male cooperation in chimpanzees and of mother-son cooperation in bonobos. Finally, female chimpanzees showed intense association with a few other females, and male chimpanzees showed more uniform association across males. In bonobos, the most differentiated associations were from males towards females. Chimpanzee male association patterns mirror fundamental human male social traits and, as in humans, may have evolved as a response to strong between-group competition. The lack of such a pattern in a closely related species with a lower degree of between-group competition further supports this notion.

KEYWORDS:

Pan paniscus; Pan troglodytes; competition; kinship; sexual segregation; sociality

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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