Gioco sociale nel lemure sifaka diadema (Propithecus diadema) della foresta di Maromizaha (Madagascar) come possibile indicatore di selezione contro l'aggressione.

Cooperation and competition coexist within social animals. Selection against aggression has been proposed as a mechanism to promote cooperation in highly tolerant species and non-aggressive competition over resources. Play behavior, especially play fighting, borrows patterns from the aggressive context and - depending on the more or less offensive modality - may offer insights on how cooperation and competition are balanced around resources. Play fighting is particularly susceptible to escalating into aggression, so animals often use facial expressions (i.e. play face) to convey playful intentions and avoid misunderstanding. The automatic replication of the play face within 1s (Rapid Facial Mimicry; RFM) may indicate whether the playful mood is transferred from an individual to another (emotional contagion) and therefore shared to keep the interaction as ‘playful’. Play modalities in relation to selection against aggression and RFM have never been investigated within Strepsirrhini. This study focused on diademed sifakas (Propithecus diadema), a tolerant and playful lemur species ideal for exploring whether the use of play is compatible with selection against aggression and whether the phenomenon of RFM is present. Data on aggression, grooming, and social play interactions were collected in four habituated groups of wild Diademed sifakas living in the Maromizaha rainforest (eastern Madagascar). A total of 32 individually identified subjects (6 immatures, 9 juveniles, and 17 adults) were sampled over four months. The study explored the influence of individual factors (age, sex) and social factors (rank) on play, using aggression and grooming as control behaviors. It also examined the relationship between play, aggression, and grooming social networks. Finally, the presence of RFM was verified through frame-by-frame behavioral coding analysis of the play sessions. Statistical analyses were conducted using SPSS and R. As expected, play - unlike aggression and grooming - decreased with age but persisted in adults. Supporting the selection against aggression hypothesis, play was more common between individuals of similar rank, who needed to compete the most due to their close social status. While no difference in play rates concerning sex was found, females’ aggression and play networks positively correlated, indicating a competitive use of play by females, the dominant sex. Conversely, in males, a positive trend between play and grooming networks was found, potentially reflecting an affiliative use of play. Finally, this study demonstrated for the first time the occurrence of RFM in a species of Strepsirrhini. These findings suggest that in Diademed sifakas, play may have different functions for males and females, with males possibly using it to affiliate (cooperation) and females using it in a competitive way to reduce in-group aggression. Finally, the presence of RFM indicates the possible contagion of the playful mood, but further investigation of the social factors modulating RFM are necessary.