Theresa Elizabeth Gildner

THERESA E. GILDNER, then a graduate student at University of Oregon, Eugene, Oregon, was awarded a grant in April 2016 to aid research on ‘Life History Tradeoffs Between Testosterone and Immune Function: Testing the Immunocompetence Handicap Hypothesis,’ supervised by Dr. J.Josh Snodgrass. The hormone testosterone plays a key role in energy allocation and the development of male characteristics. Furthermore, evidence suggests that testosterone has negative immune effects. Testosterone is therefore hypothesized to mediate energetic trade-offs between male reproductive effort and immunity. However, associations between testosterone and immune function in humans are not well established. This study tests these relationships among indigenous Ecuadorian Shuar to assess how testosterone levels influence parasitic disease risk. Microscope slides were prepared from fecal samples to measure parasite load. Additionally, saliva samples were collected in the morning and evening for three days and analyzed in lab to establish participant average morning and evening testosterone levels. Results indicate that men in urban environments exhibit higher parasite loads than men in more rural communities, perhaps due to increased contact with domestic animals and altered testosterone levels. Furthermore, men with higher evening testosterone exhibit significantly higher parasite loads, suggesting a trade-off exists between male investment in reproductive effort and immune function. Infection patterns identified in this study help inform future treatment programs by highlighting how physiological and environmental factors influence disease risk. These findings have also been used to facilitate the treatment of infected Shuar participants and advocate for improved healthcare.