Behavioral Thermoregulation during Dehydration and Osmotic Loading of the Desert Iguana

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Abstract
Dehydration to 80% initial body weight had no effect on the skin and core temperatures at which desert iguanas exited the hot or cold side of an electronic shuttle box. Hyperosmotic NaCl loading resulted in a significant decrease in the upper threshold skin temperature (44.23 ± 0.07 to 43.82 ± 0.08 C) and both the lower threshold skin (37.52 ± 0.16 to 34.93 ± 0.20 C) and core (39.28 ± 0.10 to 37.05 ± 0.25 C) temperatures. Hypoosmotic NaCl loading resulted in a significantly higher upper threshold skin temperature (42.84 ± 0.09 to 43.44 ± 0.08 C) but significant decreases in lower threshold skin (34.93 ± 0.11 to 32.11 ± 0.14 C) and core (35.34 ± 0.11 to 33.97 ± 0.14 C) temperatures. While changes in thermoregulatory behavior can be correlated with changes in plasma osmolality, shifts in the lower behavioral threshold during osmotic manipulation may be due to ionic rather than osmotic influences.