Changes in solar ultraviolet (UV) radiation have been proposed as a possible factor contributing to seeming increases in hind-limb malformations in anuran amphibians in North America. One purpose of this study was to reproduce results from an earlier experiment (G.T. Ankley, J.E. Tietge, D.L. DeFoe, K.M. Jensen, G.W. Holcombe, E.J. Durhan, and S.A. Diamond. 1998. Environ. Toxicol. Chem. 17: 25302542) in which Rana pipiens (northern leopard frog) developed hind-limb ectromelia and ectrodactyly when exposed to an artificial source of UV radiation in the laboratory. Additionally, we sought to assess the effects of natural sunlight on survival and development in this species. Animals exposed to UV radiation in the laboratory from stage 2526 (just prior to hind-limb development) through forelimb emergence exhibited a dose-dependent elevation of hind-limb dysmorphogenesis. The observed malformations usually were bilateral and typically symmetrical, and consisted primarily of missing and reduced digits. Exposure of animals at this life stage to full intensity natural sunlight caused significant mortality, while exposure to screened sunlight (ca. 5060% of ambient) resulted in an elevated incidence of abnormal hind limb pathology (ectromelia, ectrodactyly) identical to that observed in organisms exposed to UV radiation in the laboratory. Owing to uncertainties in dose extrapolation, for example, in the context of animal behavior, the potential significance of our results in terms of explaining adverse effects in amphibians from the field is as yet unclear.
