Acclimation, temperature selection, and heat exchange in the turtle, Chrysemys scripta

Turtles acclimated to temperatures between 3 and 19 degrees C were placed in a thermal gradient. The animals usually selected temperatures above 28 degrees C within 1 h after placement in the gradient, attaining a final thermal preferendum between 31 and 33 degrees C. Turtles placed in the gradient for extended periods of time were more active during the day; the temperature selected was not related to activity or time of day. Turtles were transferred from a constant temperature bath at 10 or 30 degrees C to a calorimeter at 30 or 10 degrees C. Mean body temperature (Tb) and temperatures of the heart (The), brain (Tbr), and cloaca (Tcl) as well as heart rate were continuously monitored. In a 0.76-kg turtle, temperatures increased to two-thirds of the final difference between the initial temperature and the final temperature in the following times (min): Tb, 5.5; The, 6.0; Tcl, 9.0. The increase in Tbr varied depending on whether the head was extended or retracted. Rapid changes in ambient water temperature had relatively little effect on the heart rate of a submerged turtle. Heart rates were closely related to The and were practically independent of brain temperature.