Unveiling the Role of Social Tolerance in Play and Facial Communication in the Genus Macaca

Play enhances social competence and promotes bonding. In play sessions, individuals learn to communicate using signals, particularly facial expressions. The role of play signals varies according to a species social style. Macaque societies vary on a gradient ranging from intolerant (Grade 1) to tolerant (Grade 4). Tolerant macaques show less rank- and kin-constrained relationships than despotic macaques. We compared the playful signal modality and mimicry in two species of macaques placed at the opposite of this scale: Macaca fuscata (Grade 1) and Macaca tonkeana (Grade 4). We focused on facial expressions which are frequently observed during play. We considered both specific (Play Face and Full Play Face) and unspecific playful expressions (Bared-teeth , Lip-smacking and Scalp Retraction). Compared to despotic species, tolerant species show redundancy and complexity of signals (Maestripieri, 1999; Waller and Micheletta, 2013). Compared to Japanese macaques, Tonkean macaques showed a higher level of unspecific expressions during playful interactions. Considering specific playful expressions, we found that M. tonkeana had a higher frequency of Full Play Faces but M. fuscata expressed more Play Faces. Both specific and unspecific facial expressions were mainly performed when the animals were in direct visual contact. This result suggests that the emission of facial expressions should be intentionally used to communicate a positive playful mood. We also found that M. tonkeana individuals who spent much time playing together, also performed the most long-lasting Full Play Faces. However, this correlation was not observed in M. fuscata. Tonkean macaques engaged in longer play sessions compared to Japanese macaques. In comparison, the play interactions of Japanese macaques appear extremely fragmented suggesting a high level of competition between players.