The effects of temperature and steroids [testosterone (T), estradiol (E2), and cortico-sterone (B)] on premetamorphic growth and development were investigated in the toad (Bufo boreas). The effects of steroids were both temperature and age dependent. In the first experiment, steroids (1.1–1.4 μM) were administered by dissolving them in the water beginning 1 day after hatching at 22°C or 27°C. At 22°C, B inhibited growth (P < 0.001) but had no significant effect on development. Forelegs never emerged in B-treated animals and all died before complete tail resorption. Discontinuation of B treatment allowed normal growth and metamorphosis, but the resulting post-metamorphic animals were significantly shorter (snout-vent length, P < 0.001) than after other treatments. At 22°C, T and E2 had no effect on larval growth and development or size at metamorphosis (P > 0.05), but T induced early foreleg emergence (FLE) (P < 0.005). At 27°C, B was fatal after 2 weeks of treatment, and T and E2 inhibited growth (P < 0.001) and development (P < 0.001), but did not affect time to FLE.

In a second experiment at 27°C, treatment with 1.1 μM B starting 15 days after hatching induced early metamorphic events (P < 0.001), such as tail resorption and emergence of the left foreleg (but not the right), but jaw and head restructuring failed to occur. All B-treated animals died before complete tail resorption. © 1993 Wiley-Liss, Inc.

In a third experiment, 0.275 and 1.11 μM B, starting at day 43 (stage 43), induced early FLE (P < 0.05) and decreased snout-vent length at tail resorption (P < 0.005) without a dose effect. A higher dose of B (4.44 μM) decreased snout-vent length at tail resorption and time to FLE (P < 0.05) but did not affect body weight at metamorphosis (P > 0.05). Animals in this experiment survived to complete tail resorption and transformed normally. The actions of B in these experiments closely resemble those observed with administration of thyroid hormones, suggesting that steroids may interact with endogenous thyroid hormones.