Maternal rank and offspring rank in vervet monkeys: An appraisal of the mechanisms of rank acquisition

Abstract

In two troops of vervet monkeys ( Cercopithecus aethiops sabaeus) in Barbados, maternal rank predicted the outcomes of 85.5% of all dyadic aggressive interactions between juveniles and 94.1% of those interactions that occurred in the presence of the juveniles' mothers. This suggests a strong association of maternal rank with offspring rank. Maternal interventions occurred in less than 4% of juvenile interactions, and their frequency was correlated with maternal rank. The social contexts in which maternal interventions occurred seem initially to suggest that their primary role is in the maintenance rather than acquisition of offspring rank. However, this is because offspring acquire a dependent rank immediately below their mothers from the onset. The developmental sequence of aggressive, submissive and deference behaviours of infants suggests that they do not passively accept their mothers' rank prior to being involved in interactions themselves. The frequency of aggression by adult females against juveniles is correlated with maternal rank, and is higher for female than for male juveniles. It is directed at infants prior to the time at which the infants' behaviour allows one to assign them ranks. We conclude that aggression by adult females, and the threat of maternal intervention, are primarily responsible for controlling the acquisition and maintenance of offspring rank in vervets.