Thermoregulation by Juvenile Toads of Bufo woodhousei in the Field and in the Laboratory

Abstract

Patterns of body temperatures of newly metamorphosed toads (Bufo woodhousei) were studied in the field and in the laboratory. In the field, environmental temperatures experienced by the juvenile toads varied from day to day and hour to hour. When average substrate temperatures were below 27 C, body temperatures closely resembled substrate temperature, but when substrate temperatures exceeded 28 C, body temperatures remained below substrate temperature. Analyses with biophysical models and behavior of juvenile toads suggest that the juveniles actively avoid high body temperatures. In a laboratory thermal gradient, juvenile toads selected body temperatures of 24-32 C, a range at which locomotory abilities are maximized. When deprived of food for 48 h, however, the toads selected significantly lower body temperatures (24-28 C) that would reduce metabolic demands. Similarly, when allowed to select temperatures in a thermal gradient constructed of dry sand, the toads selected lower body temperatures (17-20 C), presumably decreasing rates of evaporative water loss. This study suggests that the mechanisms and execution of thermoregulation in B. woodhousei are complexly interrelated with several aspects of the environment and the physiological state of the animal.