Associations between early life experience, chronic HPA axis activity, and adult social rank in rhesus monkeys

ABSTRACT

Early life experience and socioeconomic status (SES) are well-established predictors of health outcomes in people. Both factors likely influence health outcomes via hypothalamic-pituitary-adrenal (HPA) axis regulation. However, it is unclear how early experience and HPA axis activity influence adult social status. We studied differentially reared female rhesus monkeys (Macaca mulatta, N = 90) as models to test the hypothesis that chronic HPA axis activity assessed via hair cortisol concentrations (HCCs) mediated the relationship between early life experience and adult social rank. We found that mother-peer-reared (MPR) monkeys acquired higher social ranks than either of the two nursery-reared (NR) groups (peer-reared, PR, or surrogate-peer-reared, SPR monkeys) (β = −0.07, t₍₈₉₎ = −2.16, p = 0.034). We also found that MPR HCCs were lower during the juvenile period at 18 months (F_(2,25) = 3.49, p = 0.047). Furthermore, for MPR but not NR monkeys, changes in HCCs from 18 to 24 months (r_(s) = −0.627, p = 0.039) and adult HCCs (r_(s) = −0.321, p = 0.03) were negatively correlated with adult social rank. These findings suggest that chronic HPA axis regulation in juvenility, and perhaps in adulthood, may influence adult social status for primates that experience typical early rearing. However, early life adversity may result in dissociation between neuroendocrine stress regulation and adult social competence, which may be risk factors for adverse health outcomes.

KEYWORDS:

• Early experience
• social rank
• cortisol
• HPA axis
• Macaca mulatta

Acknowledgements

We thank Ryan McNeill, Kristen Byers, and Ashley Murphy for assistance with hair sample collection and recordings of dominance interactions. This manuscript resulted from the participation of two of us (AMD and SJS) in the National Science Foundation Symposium, “The Neurodevelopment of Stress Regulation, Social Buffering, and Fear Learning: Integration and Crosstalk,” held in Washington, DC in May 2015 (funded by NSF Grant BSC-1439258 to Dr. Megan Gunnar).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Division of Intramural Research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and by the National Institutes of Health [Grant number OD011180].