PARENT OFFSPRING CONFLICT AND MATERNAL INVESTMENT IN RHESUS MACAQUES

Infant rhesus macaques, Macaca mulatta, gained access to their mothers' nipples less frequently as they aged. At most ages, this decline was mainly a consequence of a decrease in infants' demands, and also of increases in maternal rejections. When mothers first came into oestrus, however, infants intensified their demands and became distressed, while mothers became more rejecting. These behavioural changes resulted in no changes in suckling measures. Indeed during the breeding season suckling measures were more stable than at any other time. Thus, behavioural conflict did not arise as a result of weaning, or as a result of mothers enforcing a decrease in suckling frequency. Differences in suckling measures between mothers who conceived and those who did not were not related to differences in demanding behaviour on the part of infants, but rather to differences in maternal behaviour. Thus, while infants in both groups did not differ in their frequency of attempts to gain access to the nipple, mothers who did conceive were more rejecting, particularly during the breeding season, than mothers who did not conceive. The lower rejection rates among the latter allowed an increase in suckling frequency during the breeding season, which prevented their reproduction. It is suggested that less rejecting mothers did not reproduce in an attempt to ensure their infants' survival. © 1991 The Association for the Study of Animal Behaviour.