Effects of ultraviolet radiation on life-history stages of anurans from Ontario, Canada

Abstract

We tested the effects of ultraviolet-a (uv-a) and ultraviolet-b (uv-b) radiation on life-history stages of the anurans Bufo americanus, Hyla versicolor, Rana clamitans, and Rana sylvatica. No effect of uv-a was found on eggs or larvae even at exposures twice the intensity of normal outdoor levels. Only R. sylvatica was tested in the embryo stage. All embryos exposed to 30 min or more of artificially high intensity uv-b died. After exposure to artificially high intensity uv-b of 15 min or less, or at ecologically relevant levels, there was no effect on hatching success. The proportion of abnormal embryos after exposure to 10 or 15 min of artificially high intensity treatment was higher at 12 °C than at 20 °C. The jelly surrounding the ova can effectively reduce uv-b transmission through the egg mass. Of the four species tested, only larval R. clamitans showed some tolerance of artificially high uv-b levels, but development of the survivors was arrested and metamorphosis was not initiated. Ecologically relevant doses of uv-b had no effect on developmental period, duration of metamorphic climax, or mass at metamorphosis in B. americanus, H. versicolor, or R. sylvatica. Whereas all metamorphosed juvenile R. clamitans and R. sylvatica died after exposure to high-intensity uv-b, some B. americanus survived. Older B. americanus exposed for the same length of time had higher survivorship than younger animals. The role of uv radiation in presumed amphibian population declines is discussed.