1Department of Human Evolutionary Biology, Harvard University, 2Institute for Mind and Biology, The University of Chicago, 3Department of Anthropology, University of New Mexico
Friday 9:45-10:00, Ballroom A
Costs of reproductive competition may be important limiters for fitness in primates. In seasonal breeders, males suffer elevated mortality during the mating season. Similar effects have not been documented in non-seasonal breeders, where they may be predicted to be more subtle yet more persistent over time. We studied wild chimpanzees (Pan troglodytes) at Kanyawara, Kibale National Park, Uganda to assess whether adult males experience short-term costs associated with mating competition. We compared feeding time, aggression, urinary cortisol, and urinary C-peptide (UCP) levels on days of high mating competition (with at least one parous, estrous female present) to days of low competition. Our 12 study males spent less time feeding on days of high mating competition, with individual feeding time being negatively associated with both rate of aggression and mating success. Males had lower levels of UCP, a measure of energy balance, on these days. High-ranking males were more aggressive and had lower UCP levels overall, though the reduction in male feeding time and UCP on high competition days was unrelated to rank. Finally, high-ranking males experienced greater increases in cortisol production, relative to baseline, on days of high mating competition. Thus, mating effort in chimpanzees had measurable costs in terms of both reduced energy intake and increased physiological stress. While experienced over the short-term, these energetic costs of mating effort could in theory accumulate to constrain survival and/or limit the attainment and maintenance of high dominance rank.
Supported by the Wenner-Gren Foundation, the National Science Foundation (BCS-0925697), the International Primatological Society, the Cora du Bois Trust, and Harvard University.