Short-term, but not long-term grooming reciprocity in a species with high fission-fusion dynamics

Reciprocity allows animals to balance the costs and benefits of cooperative interactions by switching roles over time. Reciprocity can be based on two different processes: partner control and partner choice. Although not mutually exclusive, the relative roles of the two processes remain debated. We investigated grooming reciprocity in wild Geoffroy's spider monkeys (Ateles geoffroyi), a species with low grooming rates and reduced opportunities for group members to interact due to a high degree of fission-fusion dynamics. We assessed separately the roles of partner control and partner choice in grooming exchanges and investigated the factors affecting reciprocity. We found short-term reciprocity based on partner-control with reciprocation occurring within 401 s after receiving grooming. In contrast, we did not find evidence for long-term reciprocity based on partner choice. Short-term reciprocity based on partner control was not affected by kinship, whereas reduced time spent together in the same subgroup increased the probability of short-term grooming reciprocation. Our results suggest the opportunity to interact is a potent modulator of reciprocity. In species characterized by a high degree of fission-fusion dynamics and low grooming rates, short-term reciprocation based on partner control can be favoured at the expense of partner choice.