1Department of Biology, University of Pennsylvania, 2Department of Psychology, University of Massachusetts-Amherst, 3Reproductive Biology Unit, German Primate Centre, Göttingen
Saturday 2:30-2:45, Grand Ballroom II
Most studies of the vertebrate stress response rely on short-term (hours-days) measures of glucocorticoid levels. Yet, these indicators have certain limitations, which may complicate the assessment of chronic activation of the stress response. By contrast, hair cortisol concentrations represent an integrated long-term (weeks-months) measure of the mammalian activation of the hypothalamic-pituitary-adrenal axis. As this analysis is more resistant to short-term environmental perturbations and variation in sampling conditions, it may provide a useful assessment of baseline adrenal function, in conjunction with non-invasive techniques. To determine the time period represented by hair samples, we used previously validated assays to compare cortisol concentrations in hair to glucocorticoid levels in fecal samples in 27 free-ranging adult male rhesus macaques. Hormone values obtained from hair of young and middle-aged males were positively correlated with average fecal glucocorticoid levels over the 4 months preceding hair collection (rS=0.43, n=20, p=0.059). We then evaluated the relationships between hair cortisol levels and socio-demographic factors. Low hair cortisol concentrations were associated with higher rates of intrasexual grooming, lower rates of directed aggression, older age, and/or higher dominance rank. Males in a large social group had significantly higher long-term cortisol levels than males in a small social group (2-sample t-test: t=3.848, df=18, p=0.001). This first study of hair cortisol levels in free-ranging primates indicates a potential of hair hormone analysis to elucidate long-term physiological patterns in mammalian populations, in which hair shaving and re-shaving are possible. Further work is needed to determine how aging may affect hair growth rate across species.
This work was partially supported by the NSF, NSF-IGERT 0504486, University of Pennsylvania Binns-Williams Fund, DAAD grant, NIH-NCRR Grant # CM-20-P40RR003640 to the CPRC, and NIH grants RR11122 and RR00168. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NCRR, NIH or NSF.