Departmental News

Posted:  May 30, 2023 - 10:00am

Megan Cole received the Honorable Mention in the American Association of Biological Anthropologists' Student Poster Competition at this year's AABA annual meetings.  The Abstract for her poster, Individual differences in baseline cortisol and cortisol reactivity among wild chimpanzees (Pan troglodytes) at Kanyawara, is below: 

MEGAN F. COLE¹, STEPHANIE A. FOX¹, MARTIN N. MULLER^1,2, EMILY OTALI², ZARIN MACHANDA^2,3, RICHARD W. WRANGHAM^2,4, & MELISSA EMERY THOMPSON^1,2 

¹Department of Anthropology, University of New Mexico 

²Kibale Chimpanzee Project

³Department of Anthropology, Tufts University

⁴Department of Human Evolutionary Biology, Harvard University

Longitudinal human studies have revealed consistent individual variation in baseline cortisol production and cortisol reactivity, detectable in controlled experiments, and that these traits predict behavior. Among wild primates, it is difficult to evaluate these trait-level features with opportunistic sampling, i.e., individuals with higher average cortisol may experience more frequent or severe stressors. We evaluated evidence for trait-level variation in cortisol in a large, longitudinal sample (13,525 urine samples from 47 adults across 13 years) from wild chimpanzees in the Kanyawara community of Kibale National Park, Uganda. After controlling for numerous temporal, demographic, and socioecological covariates, linear mixed effects models identified significant random effects of individual identity for both males (variance=0.038, p<0.001, R²=0.42) and females (variance=0.022, p<0.001, R²=0.41). We subsequently introduce a novel approach for quantifying individual-varying baselines as the local maxima of right-skewed frequency distributions. To examine reactivity, we compared individual variation during periods of low versus high socioecological stress and isolated cortisol responses to five natural stressors: aging, rank change, group hierarchy instability, heightened reproductive effort, and reduced diet quality. For each stressor, there was an individual difference in the slope of response (p<0.001), though individuals who were more reactive to one stressor were not necessarily more reactive to another. Consistent with the principle of initial values, individuals with elevated baseline levels appeared constrained in the magnitude of their responsivity. Our results suggest that cortisol production has a trait-level component in chimpanzees and points to prospects that individual variation in adrenal function may explain some dimensions of social behavior.

This study was funded by the National Institute on Aging of the National Institutes of Health (Award R37AG049395), the National Science Foundation (BCS-2141766), and a Graduate Research Fellowship.