Gila Monsters
Field Site

Team DeNardo

Jon Davis

B.S. Biology, Northern Arizona University, 2002

Ph.D. Biology, Arizona State University, 2008


Doctoral Research Interests

Because of aridity and relatively low productivity, temperate deserts pose significant physiological challenges to organisms found there. However, many organisms persist despite these challenges. Of vertebrates, reptiles are often thought of as the best suited to desert environments. This notion provided the foundation of my research interests.

I was interested in the ways in which an organism's physiologic needs influenced its behavioral ecology. The primary question my research addressed was: given the relatively arid environment of the Sonoran desert, how does an ectothermic vertebrate maintain water balance over the long-term (i.e., months to years)? Specifically, my research focused on water balance in a desert-adapted lizard, the Gila Monster, Heloderma suspectum. My approach incorporated both laboratory and field experiments to address the following:

(1) morphologic attributes and physiologic processes that allow Gila Monsters to conserve water when it's readily available for later use during prolonged periods of drought,

(2) hormonal control of physiologic processes related to water conservation,

(3) costs and benefits of specific morphologic attributes,

(4) effect of season on hydration state in free-ranging animals, and

(5) effect of hydration state on activity levels and ultimately, energy acquisition.

Ultimately, I used water balance to better understand the interplay between water, thermal, and energy balances. Of special interest was the dynamic hierarchy that exists between these physiologic processes and the factors (i.e., environmental condition, reproductive state) that influence the hierarchy. Finally, I used my research to reevaluate the concept of homeostasis in a desert-adapted squamate reptile. For example, did Gila Monsters defend well-defined physiologic boundaries whenever possible or alternatively, did Gila Monsters simply function within broad, undefended physiologic boundaries?

Publications from work while in the DeNardo lab

Davis, J. R., and DeNardo, D. F. (2010) Seasonal patterns of body condition, hydration state, and activity of Gila Monsters (Heloderma suspectum) at a Sonoran Desert Site. Journal of Herpetology 44: 83-93.

Davis, J. R., and DeNardo, D. F. (2009) Water supplementation affects the behavioral and physiological ecology of Gila monsters (Heloderma suspectum) in the Sonoran Desert, Physiological and Biochemical Zoology 82: 739-748.

Davis, J. R., and DeNardo, D. F. (2008) Water storage compromises endurance in an active forager: evidence of a trade-off between osmoregulation and locomotor performance. Journal of Comparative Physiology A. 194: 713–718.

Davis, J. R., Taylor, E. N., and DeNardo, D. F. (2008) An automated temperature-based option for estimating surface activity and refuge use patterns in free-ranging animals. Journal of Arid Environments. 72: 1414-1422.

Davis, J. R., and DeNardo, D. F. (2007) The urinary bladder as a physiological reservoir that moderates dehydration in a large desert lizard, the Gila monster (Heloderma suspectum). Journal of Experimental Biology 210: 1472-1480.

Email suspectum@gmail.com



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