An Unexpected Audience Effect and No Indirect Reciprocity of Grooming in Wild Geoffroy's Spider Monkeys ( <i>Ateles geoffroyi</i> )

Indirect reciprocity consists of performing an act that benefits a recipient while increasing the chances of receiving cooperation from a bystander. While widespread in humans, evidence of indirect reciprocity in nonhuman animals is scarce. Indirect reciprocity may involve an audience effect if cooperation increases in the presence of an audience. We investigated indirect reciprocity and audience effects in wild Geoffroy's spider monkeys (Ateles geoffroyi). Using survival analysis, we assessed whether individuals who had recently groomed others tended to be groomed more by other group members (indirect reciprocity), and whether individuals tended to groom more when surrounded by bystanders (audience effect). We found no evidence for indirect reciprocity: individuals did not receive more grooming in the 10 min after they had recently groomed others. We also found that the presence of an audience did not increase the likelihood of grooming. Actually, male spider monkeys were less likely to groom one another in the presence of other males. We found no evidence for audience effects associated with the presence of adult males on the likelihood of grooming by subadult males. Our results suggest indirect reciprocity is absent in spider monkeys, at least in the 10-min timeframe we investigated, and contribute to the limited literature on indirect reciprocity in nonhuman animals.