Temperature Selection by Amphibian Larvae

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Abstract
Rana pipiens, Rana catesbeiana and Ambystoma tigrinum larvae, when placed in a thermal gradient (8[degree] to 38[degree]C), have the ability to select and the tendency to aggregate at specific temperatures. The modal choice temperature value was 23[degree]C for the anuran species in early spring, which increased at 30[degree]C in mid-July, indicating that the phenomenon of temperature selection may have a seasonal adaptive significance. The temperature ranges occupied by 95% of the normal Rana pipiens, Rana catesbeiana and Ambystoma tigrinum larvae, respectively, were 13 to 35[degree]C, 12 to 33[degree]C and 16 to 31[degree]C. Rearing at warm temperatures (25-27[degree]C) and a low temperature (13[degree]C) decreased the preferred temperature below that selected by control larvae reared at 20[degree]C. Hypophysectomy, thyroxine (10 [mu]g/1) and propylthiouracil (.02%) immersion seemingly impaired either the ability to select temperatures or the tendency to remain at specific temperatures although the temperature range in which these animals were found remained unchanged with respect to that of the control larvae.