Seasonal Rhythms of Development and Temperature Selection in Larval Bullfrogs, Rana catesbeiana Shaw

Abstract

Development rate and temperature selection were monitored in groups of bullfrog tadpoles during periods from early summer to early winter. After collection, the tadpoles were placed in 25°C tanks with long (16L:8D), short (8L:16D), and natural photoperiods. Developmental stages (Taylor-Kollros) were assessed at approximately 3-d intervals, and temperature selection at approximately 1-wk intervals. For the first 2 wk in the 25°C tanks, development was rapid (0.4 stages· d⁻¹) in early and midsummer but very slow (0. 02 stages· d⁻¹) in early winter. During this initial 2-wk period, the temperatures selected in early and midsummer (28.4°C) were higher than those selected in early winter (24.0°C). After 2 wk in the 25°C tanks, the long-photoperiod group (relative to the short-photoperiod group) showed a slight decrease in development in early summer, no difference in midsummer, and a definite increase in early winter. Temperature selection was not altered by photoperiod length. These results suggest that endogenous annual rhythms for development and temperature selection are present in Rana catesbeiana tadpoles.