Facial expressivity in dominant macaques is linked to group cohesion

Area of Science:

• Primate behavior
• Social cognition
• Evolutionary biology

Background:

• Social living offers primates significant advantages.
• Communication is crucial for bonding social connections.
• Primates possess highly expressive faces, suggesting a role in social bonding.

Purpose of the Study:

• To investigate the relationship between facial expressivity in dominant male rhesus macaques and their social network properties.
• To determine if individual differences in facial expressivity correlate with social outcomes.

Main Methods:

• Quantified facial expressivity using anatomically based facial movement coding in nine groups of captive rhesus macaques (Macaca mulatta).
• Assessed social network properties, including social proximity and grooming behaviors.
• Maintained uniform physical and social environments for all study groups.

Main Results:

• Dominant male macaques with higher facial expressivity exhibited greater social connectivity.
• More expressive males were associated with more cohesive social groups.
• Facial expressivity was linked to both individual social position and group-level social structure.

Conclusions:

• Inter-individual variations in facial expressivity are associated with differential social success in rhesus macaques.
• Expressive individuals tend to occupy more advantageous social positions.
• These findings support the hypothesis that facial expressivity plays a role in the selection for complex facial communication in primates.