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

Male weaponry is well understood and extensively studied across taxa,
while female weaponry remains understudied, and the reasons why females
bear similar traits are still unclear. In the horned family Bovidae, males
possess horns for sexual contests, but the presence and size of female
horns vary considerably. Previous research has suggested that female
weaponry may assist in intraspecific competition for territory and/or
serve as an anti-predator defense in more exposed species. However, these
studies did not fully explore how socio-ecological factors might influence
variation in female horn length. In this study, we revisited the impact of
socio-ecological factors on horn presence and conducted more robust tests
of their effects on relative weapon investment (WQ). Our family-level
comparative analyses (N = 115) reaffirmed that female territorial behavior
and body size are the strongest predictors of female horn presence. For
relative weapon investment, we found that among species where females bear
horns, horn investment was positively correlated with larger body size and
group size. In contrast, smaller-bodied, territorial, and monogamous
species—such as klipspringers and dik-diks—tend to invest in relatively
shorter horns. Although male horn investment did not significantly predict
female horn presence, we observed that when females did bear horns, their
size scaled positively with conspecific males. Our findings continue to
support the idea that female horn presence is primarily driven by
intraspecific competition for territories and/or anti-predator defense in
larger-bodied species, while providing new evidence that social structure
(monogamy vs. polygyny) influences female investment in mammalian
weaponry.