Social bonds predict future cooperation in male Barbary macaques, Macaca sylvanus

Abstract

Social bonds have been construed as mental representations mediating social interactions among individuals. It is problematic, however, to differentiate this mechanism from others that assume more direct exchanges and interchanges of behaviour such as reciprocity, market effects or mutualism. We used naturally occurring shifts in rates and patterns of social interactions among male Barbary macaques to test whether affiliation in the nonmating season predicts coalition formation in the mating season. We carried out 1377 h of observation of all 23 males living in a semifree-ranging bisexual group at Affenberg Salem, Germany. The mating season was characterized by significantly increased rates of aggression, male coalition formation and spontaneous submission as well as decreased rates of affiliation. Rates of coalition formation in the mating season were predicted by affiliation between these males several weeks earlier in the nonmating season after we controlled for affiliation in the mating season. We conclude that social bonding in the nonmating season may build reputations among partners that are crucial for cooperation in risk-prone agonistic coalitions against other males. From the pronounced time lag between bonding and cooperation and the fact that males largely ignored affiliation as well as agonistic patterns in the time-matched mating season, we conclude that short-term reciprocity, mutualism or market effects cannot explain these observations. Instead, we conclude that long-term reciprocity mediated by emotional book keeping may be the basic mechanism. Building on that, males may employ a mental representation of their social bonds when choosing partners for cooperative interactions.