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First published online February 6, 2004
Journal of Experimental Biology 207, 945-953 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00861

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Cloacal evaporative cooling: a previously undescribed means of increasing evaporative water loss at higher temperatures in a desert ectotherm, the Gila monster Heloderma suspectum

Dale F. DeNardo^*, Tricia E. Zubal and Ty C.M. Hoffman

Department of Biology, Arizona State University, Tempe, AZ 85287-4501, USA

View larger version (18K): [in a new window]   Fig. 1. Mean cutaneous, ventilatory and cloacal water loss rates in six Gila monsters at various experimental temperatures. Note that ventilatory EWL shows little temperature sensitivity, while cutaneous EWL increases gradually as air temperature (Ta) increases, and cloacal EWL shows a dramatic increase at Ta greater than 35°C. Vertical and horizontal error bars represent ± 1 standard error for water loss rates and chamber temperature, respectively.

View larger version (18K): [in a new window]   Fig. 2. Mean differences between air temperature (Ta) and body temperature (Tb) of six Gila monsters at five experimental temperatures. Increasing Ta led to increasing suppression of Tb (P<0.0001), and Tb was consistently lower than Ta at higher temperatures. Asterisks represent significant differences (P<0.01) between the control and diaper trial values. Vertical and horizontal error bars represent ± 1 S.E.M. for temperature suppression and chamber temperature, respectively.

View larger version (19K): [in a new window]   Fig. 3. The effect of dehydration on EWL by Gila monsters at thermally challenging temperatures. Each symbol indicates the mean value for six Gila monsters; error bars indicate ± 1 S.E.M. (A) Effect on cutaneous, ventilatory and cloacal EWL at 37.5°C and 40°C. An asterisk indicates a statistically significant (P<0.025) difference between values from hydrated and dehydrated animals. (B) Cloacal EWL of hydrated animals and dehydrated animals. Note the lack of elevated cloacal EWL at 37.5°C and attenuation of cloacal EWL at 40°C for dehydrated animals (i.e. a right shift in the EWL–temperature response curve).