Facial expressions and pair bonds in hylobatids

Abstract

Our study confirms an important role of facial expressions in maintaining pair bonds and coordinating activities in hylobatids. Data support the hypothesis that facial expressions and sociality have been linked in hylobatid and primate evolution. It is possible that larger facial repertoires may have contributed to strengthening pair bonds in primates, because richer facial repertoires provide more opportunities for FES which can effectively increase the "understanding" between partners through smoother coordination of interaction patterns. This study supports the social complexity hypothesis as the driving force for the evolution of complex communication signaling.

The expression of care: Alloparental care frequency predicts neural control of facial muscles in primates

“…In monogamous species, facial expressions have been proposed to facilitate pair bond maintenance and coordination. Previous comparative work on gibbon species did not find a relationship between the rate, repertoire size, or diversity of facial expressions and either group size or strength of monogamy (e.g., frequency of extra pair copulations, proximity) (Scheider et al 2014), or between facial repertoire composition and pair bond strength, rate of territorial synchrony, or rate of behavioral synchrony (Florkiewicz et al 2018); however, facial expression synchrony does appear to be positively related to pair bond strength in gibbons (Florkiewicz et al 2018).…”

“…This is consistent with previous work showing that group size predicts relative facial mobility in anthropoids (Dobson 2009b) and may reflect that facial expressions facilitate cohesion in larger groups. However, given that certain aspects of facial expression variation (i.e., facial expression synchrony) are predicted by certain aspects of pair bondedness (i.e., pair bond strength) in gibbons (Florkiewicz et al 2018), it is likely that more specific aspects of sociality also impact the evolution of primate facial expressions. Unfortunately, such data are not available for a wide sampling of primate species.…”

“…2014), or between facial repertoire composition and pair bond strength, rate of territorial synchrony, or rate of behavioral synchrony (Florkiewicz et al. 2018); however, facial expression synchrony does appear to be positively related to pair bond strength in gibbons (Florkiewicz et al. 2018).…”

Measuring the evolution of facial ‘expression’ using multi-species FACS

“…Although surprising given previous findings (Dobson, 2009b), the lack of statistically significant relationship might be the result of the limited variability in group-size for the species under investigation. Building on this work, a more recent study used GibbonFACS to expand the known repertoire of facial behaviours in hylobatids, and test the relationship between the strength of pair-bond and facial expressiveness, measured as repertoire use, repertoire size, and facial behaviour synchrony (Florkiewicz et al, 2018). Facial behaviour synchrony was correlated to pair-bond strength, leading to the conclusion that in these species, facial behaviours are an important way of maintaining pair-bonds via close range visual communication.…”

A Comparison of Focal and Opportunistic Sampling Methods when Studying Chimpanzee Facial and Gestural Communication

“…Primates exhibit variation in signaling: some primates interact with others frequently using communicative signals, whereas others seldom use communicative signals during social interactions. Variation in signaling behavior can be attributed to numerous factors, such as age, activity budgets, social rank, and social bond strength [Rose, 2000;Bergman and Sheehan, 2013;Florkiewicz et al, 2018]. Using the focal individual sampling method ensures that researchers do not become biased towards individuals who are more expressive, present, active, or visible than others.…”