The Time Frame of Partner Choice in the Grooming Reciprocation of Cebus apella

Recent theoretical and experimental studies argued that reciprocity is constrained by the cognitive limitations of most animals and that, when reciprocation occurs, it should necessarily be short term. In this study, we examined the time frame of partner choice in the reciprocal grooming of captive female tufted capuchin monkeys (Cebus apella). Female capuchins groomed preferentially those individuals that overall groomed them most. Tufted capuchins did sometimes reciprocate grooming immediately. We quantified the time course and probability of immediate reciprocation, and excluded from the analysis cases of immediate reciprocation. We then showed that, even excluding immediate reciprocation, female capuchins still preferred to groom those individuals that groom them most. Our results show that partner choice is not necessarily based on immediate reciprocation and suggest that capuchins are able to reciprocate over longer time frames. These findings argue against the hypothesis that long-term reciprocation is absent in species lacking sophisticated cognitive abilities. We suggest that reciprocal altruism over long time frames relies on a system of emotional bookkeeping.