The effects of thiosemicarbazide on development in the wood frog, Rana sylvatica. I. Concentration effects

The effects of exposure of Rana sylvatica tadpoles to varying concentrations (10-75 mg/liter for 4 days) of thiosemicarbazide (TSC) was studied. Exposure to concentrations of 25 mg/liter or more caused a curvature of digits, abnormal limb articulations, difficulty in swimming, and death. For all of these parameters, effects were dose dependent. Tadpoles exposed to 10 mg/liter metamorphosed significantly slower than controls while those exposed to 50 mg/liter metamorphosed significantly faster than controls. Rate of endochondral ossification in femurs and tibio-fibulas also was affected by TSC. These long bones ossified faster than in controls in both the 25- and 75-mg/liter exposure groups. R. sylvatica tadpoles respond to TSC (a known osteolathyrogen) in a manner similar to that of other species. This response appears to be due in part to an acceleration of long bone ossification and speed of metamorphosis in high-concentration exposure groups. These responses are similar but not identical to those seen in Xenopus laevis, the only other amphibian studied to date.