Comparative effects of ambient ultraviolet-B radiation on two sympatric species of Australian frogs

Declines have been observed in a number of Australian frog species, many of these at high elevations. Alpine regions in Australia are likely to be particularly subject to increases in ultraviolet-B radiation ( UV-B, 280-320 nm) because UV-B levels increase with elevation and because anthropogenic depletion of ozone has been particularly severe in the southern hemisphere. We compared survivorship of embryos and tadpoles of a declining species of frog, Litoria verreauxii alpina, with those of a sympatric nondeclining species, Crinia signifera, under three ambient UV-B treatments, unshielded, control, and UV-B-excluding. Experiments were conducted in artificial water bodies established at three different elevations (1365, 1600, and 1930 m) in the Snowy Mountains of southeastern Australia. The exclusion of UV-B significantly enhanced survival of L. v. alpina (declining species) at all elevations. Overall, the probability of dying was highest in the unshielded treatments and lowest under the UV-B-excluding treatment for both species over all elevations. The probability of dying was significantly higher in L. v. alpina than in C. signifera for a given UV-B treatment at the two highest elevations. Our results support the hypothesis that ultraviolet radiation is likely to be a contributing factor in the disappearance of L. v. alpina at high elevations in southern Australia.