The Function of Mounts in Free-Ranging Barbary Macaques (Macaca sylvanus)

Generally, nonreproductive sex is thought to act as "social grease," facilitating peaceful coexistence between subjects that lack close genetic ties. However, specifc nonreproductive sexual behaviors may fulfill different functions. With this study, we aimed to test whether nonreproductive mounts in Barbary macaques are used to 1) assert dominance, 2) reinforce social relationships, and/or 3) solve conflicts. We analyzed nonreproductive mounts (N = 236) and postmount behavior in both aggressive and nonaggressive contexts, in 118 individuals belonging to two semi-free-ranging groups at La Montagne des Singes (France). As predicted by the dominance assertion hypothesis, the probability to be the mounter increased with rank difference, especially in aggressive contexts (increasing from 0.066 to 0.797 in nonaggressive contexts, and from 0.011 to 0.969 in aggressive contexts, when the rank difference was minimal vs. maximal). The strength of the social bond did not significantly predict the proportion of mounts across dyads in nonaggressive contexts, providing no support for the relationship reinforcement hypothesis. Finally, in support of the conflict resolution hypothesis, when individuals engaged in postconflict mounts, 1) the probability of being involved in further aggression decreased from 0.825 to 0.517, while 2) the probability of being involved in grooming interactions with each other increased from 0.119 to 0.606. The strength of the social bond between former opponents had no significant effect on grooming occurrence and agonistic behavior after postconflict mounts. Overall, our findings suggest that nonreproductive mounts in Barbary macaques have different functions that are not affected by the strength of the social bond.