Socioecological correlates of facial mobility in nonhuman anthropoids

Abstract

Facial mobility, or the variety of facial movements a species can produce, is likely influenced by selection for facial expression in diurnal anthropoids. The purpose of this study is to examine socioecological correlates of facial mobility independent of body size, focusing on social group size and arboreality as possible evolutionary agents. Group size was chosen because facial expressions are important for group cohesion, while arboreality may limit the utility of facial expressions. Data for 12 nonhuman anthropoid species were taken from previous studies and analyzed using a phylogenetic generalized least-squares approach. Regression results indicate that group size is a good predictor of facial mobility independent of body size. No statistical support was found for the hypothesis that arboreality constrains the evolution of facial mobility. The correlation between facial mobility and group size may be a consequence of selection for more effective facial expression to help manage conflicts and facilitate bonding in larger groups. These findings support the hypothesis that the ultimate function of facial expression is related to group cohesion.

Adaptive response to sociality and ecology drives the diversification of facial colour patterns in catarrhines

“…The divergent trends between platyrrhines and catarrhines may be explained by a higher reliance on facial expressions and displays for intraspecific communication in catarrhines [30][31][32][33][34] . For example, guenons (Cercopithecus spp.)…”

“…Differences in habitat use by platyrrhines versus catarrhines may also have a role, as visibility of facial cues is likely to be affected by the amount of clutter in the habitat and the distances among social group members. Quantitative data on the use of facial expressions 30,35 , and their relation to metrics of habitat use and social system, are crucial to test these hypotheses.…”

Yellow-bellied marmots: insights from an emergent view of sociality

“…Indeed, in other taxa, variation in the complexity of reproductive roles is associated with the individuality of facial markings [94], and colony size was associated with both bird and bat contact call individuality [95][96][97][98]. In primates, group size is associated with vocal repertoire size [99] and the ability to produce variable facial expressions [100].…”

Plain faces are more expressive: comparative study of facial colour, mobility and musculature in primates

“…Higher FCPC represents a more complexly patterned face. We estimated facial mobility at the species or genus level by applying a subset of the human facial action coding system ( [14]; electronic supplementary material) to video recordings of facial activity during feeding in zoo animals [6]. We used anatomical dissections and high-resolution photographs to document the number of facial muscles [7,9].…”

“…Complex facial patterns potentially enable higher interindividual variation within social groups and among species, facilitating recognition at either of these levels. Facial expressions are also linked to sociality; highly gregarious species produce a wider variety of facial movements [6], which may function in group cohesion by enhancing communication during conflict management and bonding [6]. Facial expressions result from the action of facial muscles that are controlled by neural pathways (facial nucleus of the pons-cranial nerve VII-and the primary motor cortex).…”