The motivations underlying food sharing in tufted capuchin monkey (Sapajus spp.)

In this work, we focused on testing one of the proximal mechanisms that have been proposed to explain cooperative behaviours such as the mutual exchange of goods and services in non-human primates. Specifically, we tested 'calculated reciprocity', according to which animals exchange food with conspecifics driven by the expectation of a return of the favour. We tested pairs of tufted capuchin monkeys (Sapajus spp.), a species known to readily exchange food, in three different experimental conditions. In the first condition, the partner, after receiving food from the subject in a first test phase, could reciprocate during a second test phase (Reciprocity). In the second condition, the partner did not have the possibility to reciprocate (Control). In the third condition, the experimenter gave the subject a quantity of food proportional to what the subject had given to the partner (Pseudoreciprocity). There was no difference in the amount of food transferred from the subject to the partner among the three experimental conditions. However, in the Pseudoreciprocity condition, capuchin monkeys increased the amount of food shared along successive test sessions. These findings suggest that the expectation of reciprocation did not motivate capuchin monkeys to share their food, although they were able to learn that sharing can lead to a reward.