The Foraging Costs of Mating Effort in Male Chimpanzees (Pan troglodytes schweinfurthii)
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Costs of mating effort can affect the reproductive strategies and lifetime fitness of male primates, but interspecific and interindividual variation in the magnitude and distribution of costs is poorly understood. Male costs have primarily been recognized in seasonally breeding species that experience concentrated periods of mating competition. Here, we examine foraging costs associated with male mating effort in chimpanzees (Pan troglodytes schweinfurthii), a polygynandrous species, in which mating opportunities occur intermittently throughout the year. To quantify male feeding, aggression, and mating, we conducted focal follows on 12 males in a wild community (Kanyawara, Kibale National Park, Uganda) for 11 mo. Males fed less on days when high-value mating opportunities (estrous parous females) were available than on days without any mating opportunities. Reductions in feeding time were related to increased rates of aggression and copulation, indicating that the proximate cause of changes in male foraging was mating effort. Surprisingly, however, there was no relationship between dominance rank and the extent to which feeding time was reduced. High costs of mating effort may reduce the degree of reproductive skew and limit the use of possessive tactics in chimpanzees. We suggest that male bonding in chimpanzees may be favored not only for its benefits but because intragroup competition is so costly. Our results complement the available data on mammals, and primates in particular, by showing that mating effort can have measurable foraging costs even in species, in which breeding is aseasonal and only moderately skewed.
KeywordsDominance Feeding costs Reproduction Sexual competition Tradeoff
We thank the Ugandan Wildlife Authority, the Ugandan National Council for Science and Technology, and the Makerere University Biological Field Station at Kanyawara for research permission and field support. For discussion and comments we thank Charles Nunn, Peter Ellison, Karen Kramer, Pawel Fedurek, and members of the Behavioral Ecology Lab at the Department of Human Evolutionary Biology, Harvard University. Paco Bertolani wrote the software used for focal data collection and generously shared it. Field assistance was provided by Francis Mugurusi, Solomon Musana, James Kyomuhendo, Wilberforce Tweheyo, Sunday John, Christopher Irumba, Friday Charles, and Edgar Mugenyi. We thank Ian Gilby and Zarin Machanda for assistance with the long-term behavioral records of the Kibale Chimpanzee Project. Statistical advice and training was provided by the AnthroTree Workshop, Roger Mundry, Natalie Cooper, and Steven Worthington. We thank R. Mundry in particular for sharing his R-code. We also thank our two anonymous reviewers, James Higham, and Joanna Setchell for their very helpful comments on earlier versions of this manuscript. Funding for A. V. Georgiev was provided by the Wenner-Gren Foundation, the National Science Foundation (DDIG BCS-0925697), the International Primatological Society, the American Society of Primatologists, the Cora du Bois Trust, Harvard University, and the Institute for Mind and Biology at the University of Chicago. Long-term data-collection by the Kibale Chimpanzee Project was supported by grants from the National Science Foundation (BCS-0849380, BCS-0648481, and IOS-0416125).
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