Effects of Ethinylestradiol and the Fungicide Prochloraz on Metamor- phosis and Thyroid Gland Morphology in Rana temporaria

Several environmental xenobiotics have been found to affect the metamorphosis of amphibians. In this study we exposed tadpoles of the Common frog Rana temporaria from hatching to metamorphosis to two known endocrine disruptors, the estrogenic pharmaceutical 17 -ethinylestradiol and the antiandrogenic/antiestrogenic fungicide prochloraz to determine their effect on 1) days to metamorphosis and size at metamorphosis, 2) body concentrations of triiodothyronine (T3) and corticosterone, and 3) thyroid morphology. We found effects of both compounds on each of these response variables. A low dose of prochloraz (115 μg/l) and all doses of ethinylestradiol also caused a delay in metamorphosis. T3 levels were elevated in metamorphs exposed to high concentration of prochloraz (252 μg/l) but the group showed a delay in metamorphosis. A low dose of prochloraz (115 μg/l) and all doses of ethinylestradiol also caused a delay in metamorphosis but no changes in T3 levels. The delayed metamorphs weighed more than controls. Thyroid histology revealed significant differences in the high prochloraz exposure group only. Ethinylestradiol and prochloraz, however not in environmentally relevant doses, may therefore impact the thyroid axis, and may cause other sublethal effects especially in combination with other stressors likely encountered.