Primate ornamentation plays a vital role in communication, not just within social groups but also between them, according to recent research. The study reveals that males of species with overlapping home ranges often exhibit striking colors or elaborate features—traits that may help reduce intergroup aggression by facilitating quick assessments of potential rivals.
These ornamental traits, selected through sexual selection, act as powerful signals of an individual’s genetic quality, health, or physical prowess. Known as dimorphic traits due to the differences they create between males and females, these features can include colorful fur or intricate body structures. Examples of such ornamentation are the golden snub-nosed monkey’s distinctive lip wart and bluish face, the mandrill’s vivid red nose and blue facial skin, the gelada baboon’s impressive mane and red chest patch, and the proboscis monkey’s unusually large nose.
A new study from the University of Zurich (UZH) has revealed an interesting connection between these dimorphic traits and how primates interact with other groups. Conducted by Stefan Lüpold from UZH’s Department of Evolutionary Biology and Environmental Studies in collaboration with Cyril Grueter from the University of Western Australia, the research suggests that the vibrant colors and elaborate body ornaments seen in many primate species serve purposes beyond attracting mates or establishing social hierarchies. These features also play a critical role in communication between different social groups.
Ornamentation Influenced by Proximity
The researchers analyzed data from 144 primate species, encompassing both monkeys and apes (prosimians and anthropoids), to explore the relationship between ornamentation and the degree of home range overlap, which reflects how much living space different groups share with their neighbors. Stefan Lüpold explained that the findings revealed a clear pattern: “Species with greater home range overlap exhibited more pronounced differences in ornamentation between the sexes. In species where groups often interact, males are more likely to develop striking traits that distinguish them from females.”
Additionally, the study found that species with greater home range overlap experienced less aggressive intergroup encounters. Conflict-related behaviors included physical confrontations, displays of strength, avoidance, displacement, vigilance, and vocal warnings. The researchers suggest that vivid physical traits might help reduce conflict between groups by enabling quick assessments of potential rivals from a distance.
A Broader Perspective on Animal Communication
“These findings challenge the traditional view that primate ornamentation is solely for competing for mates within groups,” says Lüpold. “Instead, they emphasize the importance of considering the broader social environment in which gregarious animals live, recognizing the significance of social interactions both within and between groups.” The study offers fresh insights into the evolution of primate ornamentation and deepens our understanding of the intricate world of animal communication.