The social circumstances of the maternal experience and its biobehavioral associations, in rhesus macaques (Macaca mulatta)

Motherhood is a physiologically and behaviorally demanding process. We sought to examine how such changes might be expected to alter a mother's social position within her group and whether there were physiological changes concomitant to these dynamics. We recorded contact-sitting, grooming, huddling, and proximity behavior over two birth and breeding seasons on 120 females across two mixed-sex groups of rhesus macaques (Macaca mulatta) at the California National Primate Research Center. We also collected blood samples (from all available females in the first birth season and n = 60, thereafter) for blood chemistry and cytokine assays. The reproductive stage of females exhibited a strong influence on the group's sociality. We observed meaningfully increased connectivity and investment for proximity and contact-sit beginning in late pregnancy continuing after birth, relative to non-mothers, while accounting for past offspring count. Grooming connectivity and investment meaningfully increased during pregnancy, compared to non-mothers, but decreased after the first 50 days postpartum. The number of infants in the group meaningfully increased social associations for all behaviors, except huddling, yet only in the first birth season. Maternal assortment increased, likely due to a higher number of mothers available as social partners; postpartum, however, kin assortativity did not dramatically change. Reproductive status predicted variation in biomarkers whereby pregnant females had meaningfully decreased blood chemistry measures but increased cytokines, relative to non-pregnant females. In summary, maternal social behavior exhibited marked differences across the phases of pregnancy and postpartum that exhibited distinct changes across behaviors, yet these changes in social behavior were not associated with physiological variation beyond that associated to shifts in maternal status.