The effects of ultraviolet radiation on the biology of amphibians

SYNOPSIS. Potential causes for the global decline of amphibians include habi-tat loss, disease, environmental contaminants and climate changes. The di-minishing ozone layer and consequent increase of ultraviolet-B radiation reaching the earth's surface has been hypothesized to be a mortality factor, especially in habitats otherwise undisturbed. We discuss the fundamental physics of UV and types of biological damage after exposure. A deleterious change in DNA, especially the production of pyrimidine dimers, is a main effect of UVB exposure. Damaged DNA can be repaired by enzymes such as photolyase when organisms are irradiated with UVA or visible light. We re-view studies including laboratory and field approaches on damage to amphib-ians from UVB exposure. Field studies in which embryos were exposed to natural sunlight or sunlight with UVB removed have shown conflicting re-sults: some show increased embryonic mortality after UVB exposure, whereas others show that current levels of UVB are not detrimental to amphibian em-bryos. The abiotic factors such as water depth, water color, and dissolved organic content of aquatic oviposition sites effectively reduces UVB penetra-tion through water and reduces exposure to UVB of all life history stages. Biotic factors such as jelly capsules around eggs, melanin pigmentation of eggs, and color of larvae and metamorphosed forms further reduce effective-ness of UVB penetration. We suggest areas of future research to test the hy-pothesis of the causal connection between current UVB levels and amphibian decline