Endocrine correlates and fitness consequences of variation in the mother -infant relationship in wild baboons (<i>Papio cynocephalus</i>) in Amboseli, Kenya
For animals, mammalian neonates are unusually dependent on their mothers for growth and survival, and a major goal of mammalian reproductive biology is to understand the causes and consequences of variation in infant caretaking behaviors among mothers. I investigated the endocrine correlates and fitness consequences of variation in the mother-infant relationship in five groups of wild baboons (Papio cynocephalus) of known demographic history and genealogical relationships in Amboseli, Kenya. I used non-invasive techniques to measure excreted steroid hormones from mothers across the perinatal period, and data from both patterns of behavior between parents, infants and other group members, and the long-term (>30 years) genetic, demographic and reproductive records for this population.
First, I show that fecal glucocorticoid levels during late pregnancy predicted maternal responsiveness to infant distress cries after birth. This study provides the first evidence for the preparative actions of glucocorticoids for responding to a predictable challenge (i.e. motherhood) in a wild animal population. Second, I show that sex differences in the mother-infant relationship exist during the early postnatal period, differences that are consistent with the lives of offspring as adults. I show that mothers are more permissive of male than female infants, and that maternal dominance rank and fecal estrogen levels during late pregnancy are more predictive of the suckling behavior of female than male infants. My results suggest that the mother's social world has a greater influence on the lives of female infants, and are among the first evidence of sex differences in the mother-offspring relationship during infancy in wild primates. Third, I examine the patterning of associations between adult males and new mothers during the early postnatal period and evaluate two hypotheses for why close associations (or 'friendships') between males and females might be adaptive for each sex. I show that friendships with males provide mothers and infants protection from harassment by other females, but are not associated with risk of infanticide by other adult males. Finally, I examine the predictors of birth intervals and explore the possible proximate pathways through which suckling behavior and postpartum progesterone may mediate the effects of maternal dominance rank on birth intervals in this and other mammal populations.
Anatomy & physiology;
0433: Anatomy & physiology