Thermal Tolerance of Five Salientian Amphibians during Development and Metamorphosis

Critical thermal maxima (CTM) were determined at acclimation temperatures of 10, 20, and 30 C during larval development and metamorphosis in the frog and toad species Rana sylvatica, Pseudacris triseriata, Bufo americanus, Bufo woodhousei, and Gastrophryne carolinensis. Correlations were observed between geographic distribution and CTM, and breeding time and CTM for these species. In each species there was a significant decrease in CTM during metamorphosis. This was usually followed by an increase in CTM in adults. Adults usually had lower tolerance than larvae. The decrease in CTM during metamorphosis may reflect an adjustment downward in the thermal regime of a species so that metamorphosed young will be able to tolerate the low temperatures of winter. Tadpoles of B. americanus that were starved for 12 days had significantly lower CTM than those that were fed. Intraspecific differences in CTM were observed in tadpoles of G. carolinensis from different localities and in tadpoles of B. woodhousei collected from the same locality at different times. These differences may be due to differences in early thermal experience of embryonic stages.