title: Cortisol in mother's milk across lactation reflects maternal life history and predicts infant temperament.
abstract: The maternal environment exerts important influences on offspring mass/growth, metabolism, reproduction, neurobiology, immune function, and behavior among birds, insects, reptiles, fish, and mammals. For mammals, mother's milk is an important physiological pathway for nutrient transfer and glucocorticoid signaling that potentially influences offspring growth and behavioral phenotype. Glucocorticoids in mother's milk have been associated with offspring behavioral phenotype in several mammals, but studies have been handicapped by not simultaneously evaluating milk energy density and yield. This is problematic as milk glucocorticoids and nutrients likely have simultaneous effects on offspring phenotype. We investigated mother's milk and infant temperament and growth in a cohort of rhesus macaque (Macaca mulatta) mother-infant dyads at the California National Primate Research Center (N= 108). Glucocorticoids in mother's milk, independent of available milk energy, predicted a more Nervous, less Confident temperament in both sons and daughters. We additionally found sex differences in the windows of sensitivity and the magnitude of sensitivity to maternal-origin glucocorticoids. Lower parity mothers produced milk with higher cortisol concentrations. Lastly, higher cortisol concentrations in milk were associated with greater infant weight gain across time. Taken together, these results suggest that mothers with fewer somatic resources, even in captivity, may be "programming" through cortisol signaling, behaviorally cautious offspring that prioritize growth. Glucocorticoids ingested through milk may importantly contribute to the assimilation of available milk energy, development of temperament, and orchestrate, in part, the allocation of maternal milk energy between growth and behavioral phenotype.
authors.affiliation: Department of Human Evolutionary Biology, Harvard University , 11 Divinity Avenue, Cambridge, MA 02138 , USA , ; Brain, Mind, and Behavior Unit, California National Primate Research Center, University of Califoria, One Shields Avenue , Davis CA 95616 , USA , ; Nutrition Laboratory, Smithsonian National Zoological Park , 3001 Connecticut Avenue NW, Washington, DC 20008 , USA .
authors.forename: Katie
authors.initials: K
authors.lastname: Hinde
authors.affiliation: Department of Human Evolutionary Biology, Harvard University , 11 Divinity Avenue, Cambridge, MA 02138 , USA , ; Department of Biological Sciences, Auburn University , 101 Rouse Life Science Rd, Auburn, AL, 36849 , USA .
authors.forename: Amy L
authors.initials: AL
authors.lastname: Skibiel
authors.affiliation: Division of Early Childhood, Mills College , 5000 MacArthur Blvd, Oakland, CA, 94613 , USA , and.
authors.forename: Alison B
authors.initials: AB
authors.lastname: Foster
authors.affiliation: Brain, Mind, and Behavior Unit, California National Primate Research Center, University of Califoria, One Shields Avenue , Davis CA 95616 , USA .
authors.forename: Laura
authors.initials: L
authors.lastname: Del Rosso
authors.affiliation: Brain, Mind, and Behavior Unit, California National Primate Research Center, University of Califoria, One Shields Avenue , Davis CA 95616 , USA , ; Department of Psychology, University of California Davis , One Shields Ave, Davis, CA, 95616 , USA.
authors.forename: Sally P
authors.initials: SP
authors.lastname: Mendoza
authors.affiliation: Brain, Mind, and Behavior Unit, California National Primate Research Center, University of Califoria, One Shields Avenue , Davis CA 95616 , USA , ; Department of Psychology, University of California Davis , One Shields Ave, Davis, CA, 95616 , USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Capitanio
keywords: behavioral phenotype; breast milk composition; developmental programming; glucocorticoids; life-history theory; personality.