Female grooming markets in a population of gray-cheeked mangabeys (Lophocebus albigena)

Primate female allogrooming models based on biological markets theory predict that grooming is time matched within bouts, that is, the amount of time the first female grooms predicts the amount of time the second one grooms. The models also predict that when female-female contest competition is weak, grooming is traded for grooming, but when female-female contest competition is strong, grooming may be traded for other commodities such as feeding tolerance, and grooming discrepancy between members of dyads is rank related. We tested these predictions using data collected from adult and subadult female gray-cheeked mangabeys (Lophocebus albigena) (N = 26) in 5 groups in Kibale National Park, Uganda. We found that, overall, females reciprocated in 33% of grooming bouts. Among reciprocated bouts, females in all 5 groups showed time matching. In 2 groups, we also found rank-related grooming discrepancies but showing opposite patterns to each other. Consistent with predictions based on biological markets theory, these groups may have been under greater feeding competition, revealed more by adjustments in ranging behavior than increased agonistic rates. Although these results support current allogrooming models, they also suggest that the models may become more robust if the influence of scramble competition is incorporated. In addition, they emphasize the flexibility and dynamic nature of female competitive relationships within the same population of primates.