Abstract

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