Data from: Sexually coercive male chimpanzees sire more offspring

In sexually reproducing animals, male and female reproductive strategies often conflict. In some species, males use aggression to overcome female choice, but debate persists over the extent to which this strategy is successful. Previous studies of male aggression toward females among wild chimpanzees have yielded contradictory results about the relationship between aggression and mating behavior. Critically, however, copulation frequency in primates is not always predictive of reproductive success. We analyzed a 17-year sample of behavioral and genetic data from the Kasekela chimpanzee (Pan troglodytes schweinfurthii) community in Gombe National Park, Tanzania, to test the hypothesis that male aggression toward females increases male reproductive success. We examined the effect of male aggression toward females during ovarian cycling, including periods when the females were sexually receptive (swollen) and periods when they were not. We found that, after controlling for confounding factors, male aggression during a female’s swollen periods was positively correlated with copulation frequency. However, aggression toward swollen females was not predictive of paternity. Instead, aggression by high-ranking males toward females during their nonswollen periods was positively associated with likelihood of paternity. This indicates that long-term patterns of intimidation allow high-ranking males to increase their reproductive success, supporting the sexual coercion hypothesis. To our knowledge, this is the first study to present genetic evidence of sexual coercion as an adaptive strategy in a social mammal.在有性繁殖的动物中，雄性与雌性的繁殖策略时常存在冲突。在部分物种中，雄性会通过攻击行为压制雌性的择偶选择，但学界对于该策略的实际有效程度仍存在争议。此前针对野生黑猩猩雄性对雌性的攻击行为的相关研究，在攻击行为与交配行为的关联问题上得出了相互矛盾的结果。但至关重要的一点是，灵长类动物的交配频次并非总能准确预测其繁殖成功率。我们对坦桑尼亚贡贝国家公园内卡塞拉黑猩猩（Pan troglodytes schweinfurthii）群落长达17年的行为学与遗传学数据样本进行了分析，以此验证「雄性对雌性的攻击行为可提升自身繁殖成功率」这一假说。我们分析了雄性在雌性卵巢周期内的攻击行为所产生的影响，涵盖雌性处于性接受期（阴部肿胀）与非性接受期的两个阶段。研究结果显示，在控制混淆变量后，雌性处于阴部肿胀期时雄性的攻击行为与交配频次呈正相关。但针对处于肿胀期雌性的攻击行为，却无法预测父权归属。与之相反，高顺位雄性在雌性非肿胀期的攻击行为，与父权归属的可能性呈正相关。这表明长期的胁迫行为模式可帮助高顺位雄性提升自身繁殖成功率，这一结果支持了性胁迫假说。据我们所知，本研究首次为社会性哺乳动物中，性胁迫作为一种适应性策略提供了遗传学证据。