RESUMO
Relict leopard frog (Rana [Lithobates] onca) tadpoles were obtained shortly after hatching at Gosner stage 25 and raised in aquaria maintained at 15, 20, 25, 30 and 35°C. Development was arrested in the 15°C group, and survivorship declined to 64% after 191 days. However, 80% of the surviving larvae remained alive after the temperature was increased to 25°C. Of these, 96% reached metamorphosis. Survivorship of the 20, 25 and 30°C acclimation groups was 82, 94 and 66%, respectively, whereas none survived at 35°C. Time to metamorphosis was significantly shorter for the 25°C group (67 ± 1 days), followed by the 30°C (98 ± 2 days) and 20°C (264 ± 7 days) groups. A linear 66 cm thermal gradient was used to identify temperature ranges selected by tadpoles in the different acclimation groups. Five 10°C gradients (10-20, 15-25, 20-30, 25-35 and 30-40°C) were used, and time spent in the cooler, middle and warmer thirds of the gradient was compared for 10 individuals from each acclimation group. In the coolest gradient, tadpoles from all acclimation groups selected the warmer third (>17°C) of the gradient. In the warmer gradients, tadpoles from the 20 and 25°C acclimation groups selected temperatures <29°C, while those from the 30°C acclimation group selected temperatures <33°C. Maximal burst speed for all groups was greater at experimental temperatures of 25 than 15°C. Efforts to reintroduce this species to its historical range should select habitats where water temperatures between 25 and 30°C are available during the post-hatching period.
