Context-Dependent Function of Grooming in a New World Primate

Although quite widespread across different animal taxa, grooming is an especially prominent feature of primate social life. In the social domain, grooming is thought to function as a service that individuals exchange in return for other benefits, such as other grooming, tolerance and support. However, very little is known about whether the specific social context in which grooming interactions occur may influence its function. The goal of this study was to analyse the function grooming serves in different social contexts in a New World primate species. Specifically, we tested whether grooming was exchanged as a service exchanged for tolerance in a feeding context and an infant handling context. Study subjects were 9 adult females belonging to a wild group of tufted capuchin monkeys (Cebus apella nigritus) in Iguazú National Park, Argentina. Data on grooming, co-feeding on contestable resources (as a measure of tolerance), and infant handling among females were collected over a 16-month period via focal sampling, ad libitum and instantaneous sampling. Our results indicate that in the long-term grooming seems to function as a service given in exchange for tolerance during feeding (i.e. the more grooming is received, the more tolerance is given). In contrast, in the context of infant handling grooming does not seem to represent a tradable service, but it may function as a signal of benign intent. These findings provide evidence for a multi-faceted function of grooming in different social contexts. It can be performed either as a service in return for benefits or as positive signal to facilitate social interactions.