Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation
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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 betweengroup 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 speciesdifferences 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.
Surbeck , M , Girard-Buttoz , C , Boesch , C , Crockford , C , Fruth , B , Hohmann , G , Langergraber , K E , Zuberbühler , K , Wittig , R M & Mundry , R 2017 , ' Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation ' , Royal Society Open Science , vol. 4 , no. 5 , 161081 . https://doi.org/10.1098/rsos.161081
Royal Society Open Science
Copyright © 2017 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.
DescriptionM.S. thanks the Leaky Foundation, the Wenner Gren Foundation, the National Geographic Society, Basler Stiftung fuer Biologische Forschung and the SNF. B.F. and G.H. thank the DFG, DAAD, National Geographic Society, Leakey Foundation, Volkswagen Foundation and Ludwig Maximilians Universitaet Muenchen for funding this research. K.E.L. thanks the Leakey Foundation for funding. K.Z. acknowledges the Royal Zoological Society of Scotland for providing core funding to the Budongo Conservation Field Station, and the European Research Council (grant PRILANG 283871) for providing core funding for the research. M.S., C.B., C.G.-B., C.C., R.M.W. and G.H. thank the Max Planck Society for funding.
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