Contact aggression differently predicts risk of injury in wild male and female chimpanzees ( Pan troglodytes schweinfurthii )

Injuries are a significant, recurring stressor across the lifespan. In species where injuries occur primarily from conspecific aggression, injury risk is expected to most affect those who are targeted for aggression or who are physically or socially disadvantaged. We test that assumption by examining patterns and predictors of injury in two longitudinal datasets comprising 955 injuries sustained by wild East African chimpanzees (Pan troglodytes schweinfurthii) in Gombe and Kibale National Parks. Most injuries were open wounds, and most such wounds were inflicted by conspecifics, particularly adult males. Female injury risk was strongly predicted by the rate of contact aggression received and increased for females with sexual swellings. Although socially dominant to females, adult males were injured more often. Receiving contact aggression did not predict male injury risk in either population. In Kibale, high-ranking males and those most aggressive to others received the most injuries, adding to evidence from this species that success in an intensely competitive mating market involves costly and persistent trade-offs with somatic health. Our results demonstrate that injury risk cannot be inferred from patterns of aggression alone. In particular, sexual selection on male physical traits and competitive behaviour escalates risks from male–male conflict.