Horns honestly advertise parasite infection in male and female African buffalo

The evolution and maintenance of elaborate secondary sexual characters in males have been the subject of intense interest since Darwin's time. Parasite-mediated sexual selection (PMSS) suggests that elaborate ornaments serve as honest indicators of male health and parasite resistance. Studies testing this key prediction of PMSS have largely focused on ornaments, with the role parasites might play in the maintenance of elaborate weapons being relatively understudied. Here, we tested whether weapon (horn) size was an indicator of health status in male and female African buffalo, Syncerus caffer. We examined whether individuals with larger horns were less likely to be infected with parasites, and had lower parasite loads and stronger immune systems. In males, horn size was significantly negatively correlated with the number of different parasites infecting an individual (parasite richness), the likelihood of infection with strongyle nematodes and coccidia, and strongyle intensity. In females, horn size was significantly negatively correlated with parasite richness, occurrence of coccidia infection, coccidia intensity and white blood cell count. These findings were robust when the effects of body condition, age and season were controlled for, consistent with the idea that horns function as honest indicators of health in both sexes. Our study provides new insight into the evolution and maintenance of elaborate weapons in mammals, suggesting a role for PMSS in both males and females.