Reciprocal Signaling During Approaches Relates to Close Relationships Within and Between Two Primate Species

Abstract

Signaling can facilitate coordination and cooperation, aiding relationship formation and maintenance across social animals. Reciprocal signaling may reflect equitable social motivation, thereby supporting coordination and bonding, especially in social systems that face increased social coordination challenges. To examine the link between signaling reciprocity and social bonding across social systems with different levels of coordination challenges, we studied two Western chimpanzee (Pan troglodytes verus) and two sooty mangabey (Cercocebus atys atys) groups sharing the same environment. We evaluated how reciprocity of non-agonistic signaling - equitable signaling initiation during approaches – differed depending on variation in social bond strength and grooming relationship differentiation within and between groups. Whilst both species formed well-differentiated grooming relationships, mangabeys generally allocated grooming effort to fewer group members than chimpanzees. Reciprocal signaling was positively associated with grooming frequency in both species (but more clearly in chimpanzees) and with equitable grooming effort in chimpanzees only. A strong reliance on matriline members in social bonding in mangabeys may lower coordination challenges, and thus communication needs, limiting the number of grooming and signaling partners compared with chimpanzees. In contrast, in chimpanzees, cooperation needs with non-kin may increase the number of cooperative and signaling partners. Strong fission-fusion dynamics may increase challenges related to coordination and relationship maintenance, promoting signaling production and reciprocity. Both within and between species findings provide support for the hypothesis that social bonding patterns and social complexity influence the propensity to signal reciprocally, potentially influencing aspects of signaling evolution.

Keywords

• social bonding
• dyadic signaling reciprocity
• fission-fusion dynamics
• complex social systems