Temperature Selection during Development in a Montane Anuran Species, Rana cascadae

Abstract

Temperature selection in Rana cascadae tadpoles and adults was studied in the field and in the laboratory. In a mountain pond, temperatures spanned 8-30 C in the late afternoon and 5-12 C during the early morning. Tadpoles formed dense aggregations in the warmer portions of the pond during the afternoon and night and always selected the warmer portions of the pond. In the laboratory, studies in a temperature gradient showed that (1) premetamorphic tadpoles had high selected temperatures (27.3 ± 0.6 C); (2) early metamorphic tadpoles selected the warmest temperatures (28.8 ± 0.4 C) and had the lowest level of activity; and (3) late metamorphic tadpoles (19.0 ± 0.6 C), froglets (14.5 ± 0.4 C), and 2-yr-old adults (16.0 ± 0.6 C) selected much lower temperatures. Temperature selection in tadpoles acclimated to 7 C (CA) was compared with that of tadpoles acclimated to 21 C (WA). In premetamorphic and metamorphic tadpoles, the CA groups selected lower temperatures than the corresponding WA group. In contrast, little difference was found between the two acclimation groups in late metamorphic tadpoles. Temperature appears to play an important role in tadpole distribution. The variations in selected temperature for the different developmental stages presumably reflect changing physiological requirements and modes of environmental optimization during maturation.