Meeting Abstract

19.5  Jan. 5  The effect of hydration state on activity in a free-ranging Sonoran Desert lizard, the Gila Monster, Heloderma suspectum. DAVIS, J.R.**; DENARDO, D.F.; Arizona State University, Tempe j.davis@asu.edu

North American deserts can present significant challenges to animals because of variable, often extreme temperatures and limited energy and water resources. Challenges to fundamental physiological processes (e.g., thermoregulation, energy balance, and osmoregulation) are exacerbated most during summer drought due to the combination of high temperatures and low energy and water availability. Under such conditions, activity of many animals is constrained resulting in trade-offs between fundamental physiological processes. In reptiles, environmental temperature is most often identified as a proximate factor constraining activity, yet the widespread and reliable response to rainfall in desert reptiles suggests that water availability may also be an important proximate factor directly influencing activity patterns. To separate the influence of water availability from those of temperature and seasonality, we used a variety of physiological and biotelemetric approaches to conduct a manipulative field experiment testing the hypothesis that activity is constrained by an animal�s hydration state. We randomly assigned 24 radio-telemetered, temperature datalogger implanted Gila Monsters, Heloderma suspectum, at a Sonoran Desert field site to one of two treatment groups: Water (H2O) or Control (CON). Once to twice monthly, H2O lizards received 50ml of water via an intragastric tube while CON lizards received a sham treatment. We measured plasma osmolality, body mass, and tail volume monthly, and used temperature-based activity estimation (TBAE) to estimate activity patterns of each lizard. We then compared activity and body condition characteristics between the water-supplemented and control lizards to determine whether hydration state constrains activity in this species.