The role of between-group signaling in the evolution of primate ornamentation
Gregarious mammals interact to varying degrees and in a variety of ways with neighboring groups. Since navigating this wider social environment via conventional means (social knowledge) may be challenging, we hypothesize that between-group socio-spatial dynamics have exerted strong selection on phenotypic markers of individual identity, quality, and competitive ability. Ornaments are sexually selected decorative traits with far-reaching signaling potential. Here, we examined the links between sexual dimorphism in ornamentation, home range use and encounter rates across 144 primate species in a Bayesian framework. We show that home range overlap (shared space among neighbors), an indicator of the complexity of between-group interactions (but not necessarily male-male competition), is positively associated with dimorphism in ornamentation. We find no clear effect for between-group encounter rates. We also find that inter-group interactions were less agonistic when there was greater home range overlap. Taken together, these findings indicate that ornaments play a hitherto underappreciated role in signaling to conspecifics outside the realms of their home groups.Ornaments are traits associated with sexual selection, such as colorful fur or elaborate body features, which signal important information about an individual’s genetic quality and physical strength. We propose that communicating this information via ornaments is particularly crucial in between-group interactions, where individuals encounter unfamiliar members of neighboring groups. By analyzing data from 144 primate species, we found that species with a higher degree of home range overlap (shared living spaces among neighboring groups) exhibited greater levels of dimorphism in ornamentation. Additionally, we discovered that interactions between groups were less aggressive when there was more home range overlap. These findings suggest that ornaments play a significant, previously underestimated role in communication between groups, not just within an individual’s home group.
