Western fence lizards, Sceloporus occidentalis, inhabiting the Mojave desert can face long periods of drought leading to dehydration and starvation. To examine behavioral and hormonal responses to such physiological stress, I deprived lizards of food and water in the laboratory to mimic conditions in the wild and measured their activity level (amount of time spent above ground) and their plasma levels of corticosterone and thyroxine. To identify responses that were a result of altered thermoregulation, I kept lizards either in a thermal gradient, where they were able to behaviorally alter their environmental temperature, or in thermal constancy, where they experienced a uniform environmental temperature throughout the day. Food-deprived lizards in both thermal regimes had lower levels of activity and elevated levels of corticosterone than controls. Among food-deprived lizards, those in thermal constancy had lower levels of thyroxine and corticosterone than lizards in the gradient. This suggests that lizards make compensatory hormonal adjustments to low food conditions when they are unable to select varied thermal environments. Among food-deprived lizards in the gradient, there was substantial interindividual variability. Individuals that remained the most active experienced the largest changes in most physiological measures (e.g., weight loss, hematocrit, osmolality, corticosterone). This suggests that the lizards in the wild that remain the most active during drought are the most physiologically affected portion of the population. Such individual variation in behavioral and physiological responses can lead to biased analysis of stress in a natural population. erpetology, Vol. 29, No. 3, p. 345-351, 1995 95 Society for the Study of Amphibians and Reptiles l ehavioral Responses to F od and Water i i a Lizard (Sceloporus o cidentalis): i s or sse sing Stre s in a Natural Population Animals respond both behaviorally and hormonally to physiologically stressful conditions. They simultaneously engage in behaviors that reduce exposure to severe environments and secrete hormones to activate physiological sys1 Present Address: Department of Zoology, University of Texas, Austin, Texas 78712, USA. tems that help mitigate the disturbance to their internal environment. For example, animals facing very dry conditions seek water and secrete hormones (antidiuretic hormone, aldosterone) involved in water conservation (Stricker, 1988); animals deprived of food increase foraging behaviors as well as alter the secretion of hormones (glucocorticoid, thyroxine) that affect the catabolism of fats and metabolic rate (Marthat help mitigate the disturbance to heir al environment. For example, animals i very dry conditions eek water and se345 This content downloaded from 157.55.39.177 on Wed, 16 Nov 2016 04:21:06 UTC All use subject to http://about.jstor.org/terms
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