Stress and Immune Responses to Dehydration in Helodermatids

Moeller, Karla School of Life Sciences Arizona State University Tempe, Arizona, USA karla.moeller@asu.edu

DeNardo, Dale F. School of Life Sciences Arizona State University Tempe, Arizona, USA

Brashears, Jacqueline A. Natural Sciences Department LaGuardia Community College Long Island City, New York USA

Annual droughts are a challenge to water balance for many animals living in seasonally dry habitats. Some animals manage to maintain water balance during these dry seasons, while others tolerate dehydration. The Gila Monster (Heloderma suspectum) and Mexican Beaded Lizards (Heloderma horridum) both experience a three-or-more month drought during which behaviors shift to reduce water loss and dehydration may be tolerated. In some vertebrates, dehydration can cause the release of stress hormones (e.g., corticosterone), which can in turn reduce immune function. But for helodermatids and other animals that experience dehydration over months, every year, and such responses would seem maladaptive. We investigated the effects of dehydration on plasma corticosterone levels and innate immune function in Gila Monsters and Mexican Beaded Lizards in the lab, as well as in wild Gila Monsters. In both species, dehydration alone does not cause significant increases in corticosterone. However, dehydration enhances physiological defense mechanisms including stress reactivity and certain measures of innate immune function. We also looked at how these responses vary between the two species in relation to habitat differences, as a part of a larger comparative study.