Effects of triphenyltin and pH on the growth and development of Rana lessonae and Rana esculenta tadpoles

We tested the susceptibility of parental (Rana lessonae) and hemiclonal hybrid tadpoles of the R. esculenta complex to triphenyltin (TPT), a fungicide commonly used in agriculture, at renewed concentrations of 0.11, 0.81, and 1.87 mu g/L over the entire larval period. Because habitats of R. lessonae are often characterized by a low pH and disturbed habitats such as gravel pits by high pH, we also tested whether pH 6.4 or pH 8.1 modifies their susceptibility to triphenyltin. We measured survival to metamorphosis, body mass at day 30, body mass at metamorphosis, and time to metamorphosis of individually reared tadpoles. Crosses of R. lessonae males with R. lessonae females and with two hemiclones of R. esculenta females produced tadpoles of R. lessonae, R. esculenta (GUT1) and R. esculenta (GUT2). At increasing triphenyltin concentrations, survival and growth rate decreased and time to metamorphosis increased. The GUT1 larvae of R. esculenta were the least and larvae of R. lessonae the most sensitive. The GUT2 larvae of R. esculenta were intermediate in sensitivity. The effect of pH also depended on the genotype, Tadpoles of R. lessonae had a higher growth rate and a shorter larval period at pH 6.4. The pH effect on tadpoles of R. esculenta was slight, but growth rate was lower and larval period longer at pH 6.4. Because TPT most strongly affected the larval period, exposure to TPT could decrease survival in natural ponds because of the increased risk of predation In permanent ponds or desiccation in drying ponds as well as the increased risk of additional chemical exposure. Our results indicate that the sexual parental species R. lessonae is more sensitive to environmental chemicals such as triphenyltin than is the hemiclonal hybrid R. esculenta.