School of Psychology, University of Lincoln , Lincoln LN6 7TS, UNITED KINGDOM.
The study of cooperation has been crucial to research on the evolution of social living in human and animal societies. Grooming interactions have been used as model to investigate the exchange of services in animals. Using both established and novel methodologies, this thesis examines grooming interactions and cooperation in two populations of wild Barbary macaques living in the Middle Atlas Mountains of Morocco. It is important to have a comprehensive idea of the costs and benefits of grooming interactions, and of the effect of grooming interactions on the anxiety of the grooming partners. This thesis showed that, contrary to previous studies, anxiety increased after grooming interactions in both the donor and recipient. This highlights the need to further investigate the link between grooming and emotions. Individuals may also affect the grooming interactions of other group members. This thesis showed that individuals benefit from disrupting grooming interactions of group members by gaining grooming opportunities for themselves and by stopping the group members from grooming each other, although grooming disruptions may be risky. Monkeys may affect others’ grooming interactions to favour their own social and dominance positions. A key aspect of this thesis was also to assess whether grooming is reciprocated in the short-term and which type of reciprocity (i.e. direct, indirect and generalised) play a role in the exchanges of grooming. This study showed that direct but not indirect and generalised reciprocity play a role in the exchange of grooming. While there is a wide range of evidence that direct reciprocity plays a role in the exchange of services in animals, there is little evidence of indirect and generalised reciprocity. Additionally to exchanging grooming for grooming, animals also exchange grooming for other services such as tolerance around food resource and support during agonistic interactions. In this thesis, no evidence of short-term contingency between the exchange of grooming and food tolerance was found. The exchanges of services may be little affected by recent single events, and mechanisms involving an emotional mediation based on long-term social bonds between partners may play a more important role. The capacity to make effective choices among potential social partners is an important social skill, as choosing the best available partner improves the chances to establish successful cooperative interactions. This thesis highlighted, to some extents, the importance of factors such as tolerance and relationship quality between partners, in the performances of individuals and their choice of partners to solve a cooperative task. Tolerant relationships may have been a prerequisite for the evolution of cognitively complex cooperation. Testing a comprehensive framework of predictions, this thesis brings novel contributions to the understanding of grooming interactions and cooperation in wild Barbary macaques.