The effects of early life rearing experiences and age on sociality in captive olive baboons (Papio anubis).

Abstract

Social connections within primate groups are continuously changing, and an individual's connectedness within their social network can have important consequences on morbidity and mortality. Here, we examined the effects of early life social experiences and age on social connectedness of captive female olive baboons (Papio anubis). Subjects included 54 mother-reared (MR) and 35 nursery-reared (NR) baboons (4.03 to 19.8 years of age). We conducted four 15-min focal observations and recorded all social interactions. For every possible dyad, we calculated total amount of time in proximity to one another and total amount of time spent grooming (in each direction), then used these data to create interaction matrices. We then calculated a number of direct and indirect measures of social connectedness in UCINET. Direct measures included degree centrality for grooming and proximity. Indirect measures included beta centrality for grooming and eigenvector centrality for proximity. A MANCOVA examining the effects of rearing on the three measures of direct connectedness: (1) in-degree and (2) out-degree centrality for grooming, and (3) degree centrality for proximity revealed an overall significant rearing effect, with age as a significant covariate. Subsequent univariate analyses revealed significant rearing effects on grooming out-degree centrality, in which MR females groomed conspecifics at significantly higher frequencies than NR females. There were no significant rearing effects on grooming in-degree centrality, proximity degree centrality, or any of the indirect social connectedness measures. One possible interpretation of these effects is that NR baboons might not find grooming to be intrinsically rewarding, and therefore have less motivation to groom others. Contrary to our predictions, older females did not have significantly fewer social partners, nor did they spend less time engaging in social interactions, compared to younger females. Overall, the results of this study suggest that among female baboons, early life social experiences affect social connections into adulthood, while age appears to explain less of the observed variation in social connectedness.