Long-term repeatability in social behaviour suggests stable social phenotypes in wild chimpanzees

Abstract

Consistent individual differences in social phenotypes have been observed in many animal species. Changes in demographics, dominance hierarchies or ecological factors, such as food availability or disease prevalence, are expected to influence decision-making processes regarding social interactions. Therefore, it should be expected that individuals show flexibility rather than stability in social behaviour over time to maximize the fitness benefits of social living. Understanding the processes that create and maintain social phenotypes requires data encompassing a range of socioecological settings and variation in intrinsic state or life-history stage or strategy. Using observational data spanning up to 19 years for some individuals, we demonstrate that multiple types of social behaviour are repeatable over the long term in wild chimpanzees, a long-lived species with complex fission–fusion societies. We controlled for temporal, ecological and demographic changes, limiting pseudo-repeatability. We conclude that chimpanzees living in natural ecological settings have relatively stable long-term social phenotypes over years that may be independent of life-history or reproductive strategies. Our results add to the growing body of the literature suggesting consistent individual differences in social tendencies are more likely the rule rather than the exception in group-living animals.

Group-level cooperation in chimpanzees is shaped by strong social ties

“…Chimpanzees live in a fission–fusion social system with transient and dynamic associations 61 , 64 . Association tendencies of males and females in Taï show intraindividual repeatability across days and years 71 , indicating temporally stable phenotypes of gregariousness in this population which may influence participation likelihood. Thus, to evaluate spatial proximity, we used party association data collected during the year prior to the intergroup encounter date to construct matrices of dyadic association values of all adult individuals in a community.…”

Non-genetic maternal effects shape individual differences in cortisol phenotypes in wild chimpanzees

“…If mothers vary in their rates of direct social interaction with their offspring and others, via grooming or food sharing for example, offspring may learn variable social or technical skills, such as extractive foraging (Estienne et al, 2019). The stable social phenotypes observed in adult chimpanzees includes rates of aggression, with some individuals being consistently more aggressive than others over the lifespan (Tkaczynski et al, 2020b). Therefore, long-term mother-offspring association may also behaviorally prime offspring on how to deal with social antagonism or other social challenges.…”

“…Chimpanzees have slow life histories, characterized by long gestation and maturation relative to lifespan (Bründl et al, 2021), as well as prolonged dependency on maternal care (Crockford et al, 2020; Nakamura et al, 2014; Samuni et al, 2020; Stanton et al, 2020). Recent evidence suggests that adult female chimpanzees, and thus mothers, have both relatively stable dominance hierarchies compared to males (Mielke et al, 2019) and consistent individual differences in social phenotypes that endure over several years (Tkaczynski et al, 2020b). As offspring associate almost permanently with their mothers until around the age of 12 years (Reddy and Sandel, 2020), maternal social phenotype is the key determinant of the social environment of immature offspring.…”

“…As offspring associate almost permanently with their mothers until around the age of 12 years (Reddy and Sandel, 2020), maternal social phenotype is the key determinant of the social environment of immature offspring. As some mothers are more consistently gregarious than others (Tkaczynski et al, 2020b), and social settings likely impact rates of exposure to social stressors for offspring (Sabbi et al, 2021; Tkaczynski et al, 2020a), maternal effects on average cortisol levels are perhaps not surprising in immature individuals. However, the maternal effects observed in our study apply for individuals of all age classes, suggesting that they endure beyond the immature phase.…”

Age-related change in adult chimpanzee social network integration

“…Kanyawara chimpanzees maintained stable between-individual differences in several dimensions of social integration (Table 3), i.e. certain chimpanzees were, for example, consistently more gregarious or embedded than others, similar to chimpanzees in the Taï Forest, Côte d'Ivoire (Tkaczynski et al, 2020). Thus, if social integration is important to health in chimpanzees, as it is in humans and many other species, individuals' social phenotypes could be more or less conducive to successful aging (Rowe & Kahn, 2015).…”