Social Status Shapes Maternal Style Toward Rhesus Macaque Infants in the First Year of Life

Young monkeys interact closely with caregivers and are embedded in a complex social environment. For rhesus macaques (Macaca mulatta), this environment is shaped from birth by their dams' rank within the matrilineal hierarchy. Studies have shown that subordinate female macaques experience high levels of psychosocial stress and are more protective of and attentive to their offspring. It is not clear, however, to what extent matrilineal rank explains individual differences in development, or how early in life such differences emerge. Here, we investigated the role of status in the development of 17 male infant macaques from birth to 1 year of age and identified variables at younger ages that predicted social behavior at 1 year. Most behaviors did not vary by rank; however, infants born to low-ranking dams spent less time in proximity to and being carried by their dams, compared to high-ranking infants. Also, the decline over 1 year in the sensitivity of maternal care was steeper among low-ranking dams. Initiating social play among 1-year-olds was negatively predicted by maternal cradling duration in early infancy. We discuss the importance of factors including the sex of offspring, species, and the stability of the wider social environment.