Stability and Change of Social Relationship Quality in Captive Chimpanzees (Pan troglodytes)

In social animals an individual's fitness depends partly on the quality of relationships with others. Qualitative variation in relationships has been conceptualized according to a three-dimensional structure, consisting of relationship value, compatibility, and security. However, the determinants of the components and their temporal stability are not well understood. We studied relationship quality in a newly formed group of 20 captive chimpanzees made up of several previously existing social groups. We assessed dyadic relationship quality 2 yr and again 7 yr after grouping. We confirmed the existence and stability of three relationship components and labeled them value, compatibility, and approach symmetry. Previously familiar dyads had a higher value than unfamiliar dyads, especially when they were maternally or paternally related. Compatibility was higher in dyads with only females than in dyads containing a male, but familiarity did not influence compatibility. Approach symmetry was initially higher, but later lower, in familiar than unfamiliar dyads, indicating that approach symmetry of familiar dyads decreased over time. Dyadic value and compatibility were highly stable over time, which is similar to the long relationship duration found in wild chimpanzees. In sum, relationships formed earlier in life became more valuable than those formed in later adulthood, whereas nonaggressive, compatible relationships could be formed throughout life. This suggests that for immigrating individuals, high-value relationships may be relatively difficult to establish, partly explaining why wild female chimpanzees have relatively few high-quality relationships with other females. Our study supports the multicomponent structure and durability of relationships in social species.