Date Approved

12-2020

Graduate Degree Type

Thesis

Degree Name

Health Sciences (M.H.S.)

Degree Program

Biomedical Sciences

First Advisor

Dr. Cynthia Thompson

Second Advisor

Dr. Jodee Hunt

Third Advisor

Dr. Theodore Towse

Academic Year

2020/2021

Abstract

Relative to most primate species, Japanese macaques (Macaca fuscata) experience extreme seasonal variation in thermal and ecological stressors that can impact energetic demands. To cope with these environmental changes, levels of metabolic hormones, such as cortisol and triiodothyronine, fluctuate to facilitate energetic adjustments. While previous research in primates has investigated thermal and ecological stressors individually, a combined assessment of these stressors alongside hormone levels can provide a more holistic understanding of the relationship between a primate’s thermoregulation, energetic balance, and stress. The goals of this study were to determine the effects of season, temperature and ecological stress on cortisol levels in Japanese macaques, as well as assess the relationship between cortisol and freely circulating triiodothyronine (fT3). Fecal samples were collected at Kyoto University Primate Research Institute (KUPRI) on semi-free ranging Japanese macaques and tested for cortisol and fT3 levels using enzyme-linked immunosorbent assay (ELISA). Japanese macaques did not show a significant difference in cortisol levels between seasons, although winter cortisol levels were marginally higher. During summer, there was not a significant effect of daily temperature on cortisol levels. However, in the winter, macaques showed a consistent negative relationship between cortisol levels and daily maximum temperatures. While this indicates that cortisol levels increased as maximum temperatures became colder, there was not a significant correlation with mean or minimum daily temperatures. Using activity levels as a proxy for ecological stress, there were no significant effects of mean daily group activity on cortisol levels during either season. However, there was a significant and strong positive relationship between fT3 and cortisol levels during both summer and winter seasons, with cortisol levels increasing in conjunction with fT3. Contrary to predictions, there was not a seasonal pattern in cortisol levels, although these data provide partial evidence that thermal stress can impact cortisol levels on a daily scale. Animals were provisioned foods, which may have reduced the intensity of ecological stress, possibly dampening seasonal impacts on cortisol levels. Despite these mixed results, the strong relationship between fT3 and cortisol may suggest that animals modulate metabolic hormones in a coordinated manner to cope with changing energetic needs.

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