Visual Communication and Development of Social Behaviour in gelada (Theropithecus gelada)

Play is a fertile field to examine the role of facial expressions that we share with our common ancestors because the primate play face is homologous to human laughter. Here, we focus on the use of two playful expression variants, play face (PF) and full play face (FPF) in Theropithecus gelada. We recorded the behaviours of individual belonging to two colonies of geladas living at the NaturZoo (Rheine, Germany). Data were collected during a 6-month period in 2007 (June-November), a 4-month period in 2009 (June-September) and a 2-month period in 2010 (July-August). Data showed that during ontogeny PF was replaced by FPF; in older subjects PF was virtually absent. The ontogenetic transition of facial expressions appears to reflect their different roles in communication. In a second study we assessed the capacity to reproduce rapid imitative responses (RFM) and to evaluate the impact of these responses on affiliative behaviours. Here, we demonstrated that RFM is also present in a cercopithecoid species (Theropithecus gelada) and provided evidence of the link between behavioural matching and emotional connection. In fact, in the third study, we demonstrated that individuals with higher levels of matching also display prolonged sessions of play. We propose that RFM could be grounded in the automatic perception-action coupling of sensorimotor information occurring in the mirror neuron system. The capacity to match othersࢠbehaviour could have the advantage to synchronize the activity with those of the other group members and to learn the context in which an activity should be performed. Finally, we investigated the ontogeny of RFM and found that it is also present gelada newborns and is refined in the course of the first weeks of life. This naturalistic approach gave an important contribution to previous researches on imitative behaviour suggesting that the infantࢠs capacity to respond and solicit facial expressions is critically dependent on the type of social environmental feedback received by the mother and other individuals. Our findings indicate that the building blocks of empathy linked to RFM in humans have homologous not only in apes, but also in cercopitecoids, suggesting a common evolutionary root in the basic elements of social communication.