Thermal Selection in Tadpoles of the Tailed-Frog, Ascaphus truei

Tadpoles of the tailed-frog, Ascaphus truei, exhibit distinct responses to temperature when placed in laboratory temperature gradients. Thermo-regulatory behavior is evidenced by an avoidance of temperatures above 22 C. Both first and second year tadpoles select over a wide temperature range (0-22 C), but first year animals tend to congregate below 10 C, whereas second year tadpoles aggregate above 10 C. Thermal acclimation had little influence on the preferendum of either year class, but photoperiod may alter the response of second year tadpoles to a temperature gradient.