Annie Margaret Dean

M.A. Conservation Biology 2012

Short Term Grooming Reciprocity in Blue Monkeys

Short-term decision making in the social exchanges of group-dwelling animals, such as primates, offers a means of better understanding cooperative action. As a low-cost or no-cost behavior that all group members can exchange, the way in which grooming is exchanged at the most proximate level (within a bout and across episodes) offers a useful means of examining shortterm decision making. Here I examine grooming reciprocity at several short-term time scales to assess what factors might predict whether an adult female blue monkey reciprocates grooming, how long she reciprocates grooming, and how equitable the grooming is between her and her partner over a bout. I chose predictors based on biological markets theory (Noë and Hammerstein 1994), reciprocal altruism theory (Schino and Aureli 2009), as well as field studies that have tested these theories. Predictors included measures of kinship, age, rank, sociality, agonism, infant presence, previous time spent grooming, and amount of grooming investment within the bout prior to a decision point. A female was more likely to reciprocate received grooming if neither she nor her partner had an infant, if she had received less grooming in the previous episode, if her partner’s rank was high or if the dyad’s sociality index was low. When it occurred, reciprocation lasted longer if the female had received more grooming in the prior episode, and possibly when she groomed a lower-ranking partner. Overall equitability within a bout was greater when there were more episodes, when the partner who groomed less had no infant and when the partner who groomed more had an infant. Overall, in line with previous research on biological markets, the results indicated that adult females exchanged grooming for itself as well as for a commodity (access to infants, indexed by infant presence). Results were more consistent at the longer scale of assessment (the bout), but the most proximate level of decision-making (at the end of one episode) was not easily predicted by any of my factors. 3 Therefore, even within short-term decision making, the timescale of assessment is important. It is possible that episodes represent a time scale that is too short to meaningfully capture differences in reciprocity.

I completed my undergraduate degree in Anthropology at the University of Chicago. Before arriving at Columbia, I studied partner preference in mantled howler monkeys (Alouatta palliata) during a field course in Costa Rica.