Abstract # 123:

Scheduled for Sunday, September 18, 2011 09:45 AM-10:00 AM: Session 17 (Meeting Room 408) Oral Presentation


D. Proctor1, S. P. Lambeth2, S. J. Schapiro2 and S. F. Brosnan1
1Georgia State University, Dept. of Psychology, PO Box 5010, Atlanta, GA 30302-5010, USA, 2Michale E. Keeling Center for Comparative Medicine and Research of the University of Texas M. D. Anderson Cancer Center

Copulation preferences in our closest living relative, the chimpanzee (Pan troglodytes), suggest that males prefer older females who have had previous offspring. However, this finding is counter to some behavioral models, which predict chimpanzee males, as promiscuous breeders with minimal costs to mating, should show little or no preference when choosing mating partners (i.e. should mate indiscriminately). To determine if the preferences indicated by copulations appear in other contexts, and how they interact, we examined how captive male chimpanzees’ grooming patterns varied amongst females over 108 hours of observation (male: N=22; female: N=40). Using a generalized regression model, we found that males’ preferences were based on interactions among females’ fertility status, age, and parity [F(2)=3.388, P=0.039]. First, grooming increased with increasing female parity. We further found an effect of the estrous cycle on grooming; when females were at the lowest point of their cycle, males preferentially groomed parous females at peak reproductive age [B=3.282, SE=1.194, T=2.749, P=0.009], but during maximal tumescence, males preferred the oldest multiparous females [B=-0.266, SE=0.086, T=-3.103, P=0.039]. Nulliparous females received relatively little grooming regardless of age or fertility. Thus, male chimpanzees apparently chose grooming partners based on both female’s experience and fertility, possibly indicating a two-pronged social investment strategy. Male selectivity appears to have evolved to effectively distribute costly social resources in a pattern, which may increase their overall reproductive success.