Despotic long-tailed macaques benefit others in a group service paradigm

For animals living in social groups, cooperation is a key factor to success. It has been postulated that in social systems with cooperative breeding or a tolerant dominance style, individuals will benefit each other. Cooperation is, therefore, not expected in long-tailed macaques, since they do not breed together and experience a steep unidirectional hierarchy. However, previous studies have shown that they can be prosocial in a dyadic setting. This would comply with the more recently postulated dyadic interdependence hypothesis. To be able to compare their cooperative performances with other species, we set up a group service paradigm similar to that, which has been tested in a number of other species. We presented a swing set apparatus, which an actor could pull in the middle to provide a reward to another individual but without access to the reward for the actor, to three groups of socially housed long-tailed macaques. The macaques showed prosocial behaviour in the test significantly more often than in two control condition. They preferably provided to kin. The prosocial behaviour of the despotic, individual breeding long-tailed macaques counters the cooperative breeding and self-domestication hypotheses, yet supports the dyadic interdependence hypothesis, although future studies on other macaque species with more tolerant dominance styles should elucidate the effect of dominance styles on prosociality.