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.