Untamed smile: rapid facial mimicry in wild wolves

Understanding play communication in social carnivores provides key insights into the evolution of complex signalling. In this study, the play behaviour in wild Apennine wolves, Canis lupus italicus, was investigated focusing on the relaxed open mouth (ROM), which is a ritualized signal that reduces the risk of play escalation. Using noninvasive camera trapping across five sites in the wild (115 wolves), ecologically valid data that are free from human disturbance were obtained. Our findings show that the facial muscle activation underlying ROM in wild wolves is consistent with that of captive individuals across subspecies, indicating an evolutionarily conserved function. ROM frequently preceded competitive actions, supporting the metacommunication hypothesis, which posits that specific signals modulate the interpretation of subsequent behaviours. Rapid facial mimicry (RFM), which is an automatic and fast replication of others’ expressions, was present in our group. This phenomenon, which was previously identified in domestic dogs, has never been studied in their wild counterparts. The presence of RFM, particularly in highly competitive play sessions, highlights its role in maintaining a playful mood. Therefore, RFM is not a byproduct of domestication but a naturally selected trait that is effective in play communication. Our study will provide new insights into the communicative complexity of wild carnivores and a foundation for future comparative research.