Hair Cortisol in Wild and Captive Primates: Environmental Effects and Behavioral Phenotypes
Open AccessCortisol archived in hair represents circulating concentrations averaged over the growth period of the hair. Measurement of cortisol in hair is finding wider application in animal studies of stable behavioral trends or the effects of chronic stressors. In primatology the method has only been applied to a small number of species, and only in captivity. The goal of this dissertation was first, to assess whether patterns of hair cortisol reflect biologically meaningful variation within and between wild and captive non-human primate species, and second, to apply the method to the study of behavioral and environmental effects on stress in wild non-human primate populations. These studies also make methodological contributions to the use of hair as a tool in behavioral endocrinology. I used enzyme-linked immunosorbernt assay techniques (ELISA) to measure cortisol extracted from hair samples from 653 individuals, representing 17 primate species. First, I demonstrated that hair cortisol concentrations reflect known phylogenetic, species, and age related patterns in circulating cortisol. Second, using a cross-sectional population level approach, I showed that populations of wild baboons (anubis - Papio anubis, hamadryas - P. hamadryas and their hybrids) in the Awash National Park, Ethiopia, differed in chronic cortisol profiles, specifically, I found that male hybrids have elevated and relatively variable hair cortisol. This may reflect the destabilizing effect of hybridization on bio-behavioral stress complexes. Hamadryas populations sampled during a drought in 1973, exhibited elevated hair cortisol consistent with evidence of severe nutritional stress in these populations, while both mixed hamadryas and hybrid populations exhibited variation in basal cortisol profiles consistent with hybrid dysregulation. Females of these populations did not exhibit similar patterns in hair cortisol. I demonstrated that variation in hair cortisol in wild juvenile anubis baboons is marked by infant hypercortisolism and a sharp decline in cortisol with age. These results further suggest maternal effects on offspring development, in that light-for-age juvenile males exhibited elevated hair cortisol compared to heavy-for-age animals. Finally, an analysis of vervet monkey (Chlorocebus aethiops) hair cortisol, in samples from populations occupying habitats with varying levels of human disturbance, found that male animals in habitats with high levels of human disturbance have elevated cortisol concentrations.
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