Sexual Conflict in Nonhuman Primates

Increasing appreciation that male and female reproductive strategies may be not only divergent but also incompatible has highlighted the potential importance of sexually antagonistic coevolution as a third force of sexual selection. Here, I review evidence for this mechanism in nonhuman primates. Sexual conflict has been studied primarily in its behavioral form, sexual coercion, for which relevant data still remain surprisingly limited. Nevertheless, current evidence reveals three forms of coercion: forced copulation, sexual harassment, and sexual intimidation. Many new data have confirmed the importance of forced copulation in orangutans, and clarified its variation and contexts, but have left unclear its adaptive significance. Evidence for sexual harassment and sexual intimidation has come from diverse taxa, but there are indications that the former may be expressed relatively more often in the nongregarious strepsirrhines and the latter among group-living haplorrhines. Two temporal domains for the action of sexual intimidation are suggested by evidence that it can improve male mating success both immediately and prospectively. Some researchers also suggest that female mate choice may underlie "coercion" in some taxa and that nonmating functions, such as social control, may be relevant. A key element of sexual conflict theory is female counterstrategies mitigating the costs of male adaptations. Current evidence now implicates strongly a great range of possible counterstrategies, involving female reproductive physiology, sexual behavior, and social strategies, although more data are needed to determine the effectiveness of these counterstrategies. Limited but suggestive data also indicate postcopulatory sexual conflict involving genitalia, seminal fluids, and their genetic bases.