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.
Highlights
Consistent individual differences in social phenotypes have been observed in many animal species
Except for female daily aggression, including the random intercept and slopes of individual identity significantly improved model fit, indicating that for most social behaviours involved in this study, chimpanzees showed inter-individual differences that were consistent over time and could be detected on the daily and yearly level
Our study reveals that multiple types of social behaviour are repeatable in wild chimpanzees over several years
Summary
Consistent individual differences in social phenotypes have been observed in many animal species. An individual’s physiological state may vary over time, e.g. during pregnancy and/or the rearing of offspring, in turn influencing motivation for social behaviour [30] This raises the question of why highly stable social phenotypes are so regularly observed across animal taxa. The repeatability of social behaviour has been well explored in relatively short-lived species, both in the wild [1,4,5,7] and in more controlled captive settings [6,8] In such studies, the comparatively short lifespans of the study species allow for monitoring the stability of social tendencies across different socioecological settings, such as across breeding seasons [1], different life-history stages [8], or even across generations [5]. While studies of patterns of association are clearly important for understanding the evolution of social phenotypes, for many species, navigating the social environment requires a diverse range of affiliative and agonistic behaviours
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