1Department of Evolutionary Anthropology, Duke University, 2Department of Structural Biology, Stanford University School of Medicine, 3Vaccine Research Center, National Institutes of Health, 4Department of Medicine, Perelman School of Medicine, University of Pennsylvania, 5Department of Microbiology, Perelman School of Medicine, University of Pennsylvania
Thursday All day, Clinch Concourse
In sexually reproducing animals, male and female reproductive interests often fail to align, resulting in opposing reproductive strategies. Males of many species employ aggression to overcome female choice, but debate persists over the extent to which male chimpanzees effectively use this strategy. Previous studies of male chimpanzee aggression toward females at Kanyawara (Kibale National Park, Uganda) demonstrated a positive correlation between aggression and copulation frequency, however copulation frequency in primates is not always predictive of reproductive success. We analyzed a 13-year sample of behavioral and genetic data from two chimpanzee communities in Gombe National Park, Tanzania, to test the hypothesis that male aggression toward females is positively correlated with reproductive success. We found that, similar to Kanyawara, male-female aggression over a female’s entire estrous cycle was positively correlated with copulation frequency (GLMM, p < 0.0001, controlling for male dominance rank). Further, the timing of aggression played an important role, as aggression during a female’s estrous phase was correlated with copulation frequency (p < 0.0001), while aggression during a female’s non-estrous phase was not (p = 0.48). Preliminary analysis of the genetic data demonstrated that the rate of a male’s aggression toward a given female was positively correlated with the probability of siring that female’s offspring (p < 0.001). Together, our data suggest that male chimpanzees at Gombe successfully employ a strategy of sexual coercion to increase their probability of paternity. Future analyses will incorporate dominance rank and kinship into our analytical model.
Data collection was supported by the Jane Goodall Institute, construction of the long-term database was supported by grants from the NSF (DBS-9021946, SBR-9319909, BCS-0452315, IOS-LTREB-1052693), genetic analyses were supported by grants from the NIH (R01 AI50529, R01 AI58715, P30 AI 27767), and Wroblewski was supported by a Ruth L. Kirschstein National Research Service Award (NIH F32 AI085959-03).