Sex differences in the mother–neonate relationship in wild baboons: social, experiential and hormonal correlates

Abstract

In mammals, maternal care is essential for offspring survival, yet individual differences in this care can dramatically affect offspring growth and development. Few studies have, however, investigated the sources, magnitude and consequences of naturally occurring interindividual variation in maternal care during the neonatal period. In this study, we examine several hormonal and nonhormonal predictors of naturally occurring variation in the mothereneonate relationship during the first 8 weeks of infancy in 34 wild baboon (Papio cynocephalus) mothereinfant dyads in Amboseli, Kenya. We use data on physical contact and suckling patterns to assess the quality of the mothereneonate relationship and to evaluate the extent to which variation in this relationship is predictable from perinatal ovarian steroids (i.e. faecal oestrogen and progesterone metabolites), previous infant care experience, maternal dominance rank and offspring sex. We found that newborn infants of more experienced mothers initiated higher rates of changes in mothereinfant contact than newborns of less experienced mothers. However, at each level of maternal experience, newborn males initiated higher rates of changes in mothereinfant contact than newborn females. Moreover, we found evidence suggesting that variation in suckling activity among daughters (but not sons) was predictable from maternal dominance rank and faecal oestrogen (fE) concentrations before birth. To our knowledge, our study provides the first evidence of (1) the influence of cumulative maternal experience on the mothereinfant relationship and (2) the emergence of sex differences in the mothereinfant relationship during the neonatal period in wild primates. Our results suggest that the well-documented sex differences in life history, behaviour and ecology in primates (and other social mammals) may originate very early in life. 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. For vertebrates, mammalian newborns are unusually dependent on their mothers for nourishment, transport, protection and support (Clutton-Brock 1991). Although offspring eventually transition from complete reliance on their mothers to nutritional, locomotor and social independence, the timing of these events can vary widely across individuals of the same species (Clutton-Brock 1991). Despite the critical importance of the neonatal period in the life of each individual, few studies have investigated the sources, magnitude and consequences of interindividual variation in the mothereoffspring relationship during the neonatal period in wild mammals (Altmann 1980; Bales et al. 2002). In this study, we