Territoriality, sociality and male weaponry shape horn investment in female bovids

Abstract Male weaponry is well understood and widely studied across taxa, yet female weaponry remains comparatively overlooked and the evolutionary drivers of such traits in females are still not well defined. In Bovidae, males typically use horns in sexual contests, but females show considerable variation in horn presence and size across species. Earlier research suggested female horns may function in intraspecific competition for territory or social rank, or serve as antipredator defense in exposed habitats, however, these studies did not directly test how socio-ecological factors shape variation in female horn length. In our study, we reevaluated the influence of socio-ecological factors on horn presence and rigorously tested their effects on female weapon investment (FWQ). Across family-level comparative analyses (N = 115), female territoriality, sociality, and body mass positively predicted horn presence. Among horned females (N = 80), horn investment differed among tribes and increased with sociality. Female horns did not scale with body mass and territorial and pair-bonded species—such as klipspringers and duikers—tended to have relatively shorter horns. Although male horn investment did not directly predict whether females bore horns, in species where females did, their horn investment scaled positively with that of males. Our results support female horn presence is primarily shaped by intraspecific competition and offset by cost-minimization at larger-bodied species, while providing new evidence that social selection influences female weapon investment in mammals.