Abstract
Seyfarth's model assumes that female primates derive rank-related benefits from higher-ranking females in exchange for grooming. As a consequence, the model predicts females prefer high-ranking females as grooming partners and compete for the opportunity to groom them. Therefore, allogrooming is expected to be directed up the dominance hierarchy and to occur more often between females with adjacent ranks. Although data from Old World primates generally support the model, studies on the relation between grooming and dominance rank in the New World genus Cebus have found conflicting results, showing considerable variability across groups and species. In this study, we investigated the pattern of grooming in wild tufted capuchin females (Cebus apella nigritus) in Iguazú National Park, Argentina by testing both the assumption (i.e., that females gain rank-related return benefits from grooming) and predictions (i.e., that females direct grooming up the dominance hierarchy and the majority of grooming occurs between females with adjacent ranks) of Seyfarth's model. Study subjects were 9 adult females belonging to a single group. Results showed that grooming was given in return for tolerance during naturally occurring feeding, a benefit that higher-ranking females can more easily grant. Female grooming was directed up the hierarchy and was given more often to partners with similar rank. These findings provide supporting evidence for both the assumption and predictions of Seyfarth's model and represent, more generally, the first evidence of reciprocal behavioural interchanges driven by rank-related benefits in New World female primates.
Highlights
The distribution of grooming among group members is a fundamental aspect of primate sociality with direct implications for social bonding
If grooming is exchanged for benefits best provided by high-ranking individuals, this is likely to affect how animals distribute their grooming among group members
We tested if competition for preferred grooming partners occurs by examining whether tufted capuchin females directed the majority of their grooming to females of adjacent ranks (Prediction 3); whether higher-ranking females were better able than lower-ranking females to allocate their grooming according to the rank of the recipient (Prediction 4); and whether higher-ranking females performed overall more grooming than lower-ranking females (Prediction 5)
Summary
The distribution of grooming among group members is a fundamental aspect of primate sociality with direct implications for social bonding. If grooming is exchanged for benefits best provided by high-ranking individuals, this is likely to affect how animals distribute their grooming among group members This was first noted by Seyfarth [12], who proposed a influential model to explain grooming patterns among female primates. Perry [26] suggested that C. capucinus females groom up the hierarchy following the predictions of Seyfarth’s model, whereas the opposite was found in C. olivaceus [27] and C. apella [28] These analyses tested the predictions of Seyfarth’s model by detailing the distribution of grooming among females in relation to dominance rank, few studies focused on verifying the assumption of the model (i.e., that grooming increases the likelihood of gaining rank-related return benefits; but see [26,29]). We tested if competition for preferred grooming partners occurs by examining whether tufted capuchin females directed the majority of their grooming to females of adjacent ranks (Prediction 3); whether higher-ranking females were better able than lower-ranking females to allocate their grooming according to the rank of the recipient (Prediction 4); and whether higher-ranking females performed overall more grooming than lower-ranking females (because grooming allocation in the latter was constrained by dominance relations) (Prediction 5)
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