title: First-time rhesus monkey mothers, and mothers of sons, preferentially engage in face-to-face interactions with their infants.
abstract: Face-to-face interactions between mothers and infants occur in both human and non-human primates, but there is large variability in the occurrence of these behaviors and the reason for this variability remains largely unexplored. Other types of maternal investment have been shown to be dependent on infant sex (e.g. milk production and maternal responsiveness) and maternal experience (e.g. symmetrical communication). Thus, we sought to determine whether variability in face-to-face interactions, that is, mutual gazing (MG), which are hypothesized to be important for later socio-cognitive development, could be explained by these variables. We studied 28 semi-free ranging rhesus monkey (Macaca mulatta) mother-infant dyads (6 primiparous; 12 male infants) born and reared at the Laboratory of Comparative Ethology field station at the NIH Animal Center in Poolesville, MD, across the first 90 postnatal days. Infant sex (i.e. male) was a significant predictor of maternal grooming (β ± SE = 0.359 ± 0.164, Z = 2.19, P = 0.029) whereas both parity (i.e. first time mothers) and infant sex (i.e. male) significantly predicted MG (parity: β ± SE = -0.735 ± 0.223, Z = -3.30, P < 0.001; infant sex: β ± SE = 0.436 ± 0.201, Z = 2.17, P = 0.029). Separation from the mother (outside of arm's reach) was not influenced by parity or infant sex. Together with existing literature, these findings point toward differential maternal investment for sons versus daughters. Mothers may be investing differentially in sons, behaviorally, to ensure their future social competence and thus later reproductive success. Collectively, our findings add to the literature that is beginning to identify early life experiences that may lead to sex differences in neurological and behavioral development.
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Dettmer
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.|Dipartimento di Neuroscienze, Università di Parma, Parma, Italy.
authors.forename: Stefano S K
authors.initials: SS
authors.lastname: Kaburu
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.
authors.forename: Kristen L
authors.initials: KL
authors.lastname: Byers
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Murphy
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.|Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut.
authors.forename: Emma
authors.initials: E
authors.lastname: Soneson
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Wooddell
authors.affiliation: Laboratory of Comparative Ethology, Eunice Kennedy Shriver National Institute of Child Health & Human Development, National Institutes of Health, Poolesville, Maryland.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Suomi
mesh_terms: D000818:Animals; D000836:Animals, Zoo / Q000502:physiology*; D005260:Female; D008253:Macaca mulatta / Q000502:physiology* / Q000523:psychology; D008297:Male; D008396:Maryland; D008425:Maternal Behavior
keywords: Macaca mulatta; infant sex; mother-infant interaction; mutual gaze; parity