The Effects of Ultraviolet Radiation on the Biology of Amphibians

SYNOPSIS. Potential causes for the global decline of amphibiansinclude habitat loss, disease, environmental contaminants andclimate changes. The diminishing ozone layer and consequentincrease of ultraviolet-B radiation reaching the earth's surfacehas been hypothesized to be a mortality factor, especially inhabitats otherwise undisturbed. We discuss the fundamental physicsof UV and types of biological damage after exposure. A deleteriouschange in DNA, especially the production of pyrimidine dimers,is a main effect of UVB exposure. Damaged DNA can be repairedby enzymes such as photolyase when organisms are irradiatedwith UVA or visible light. We review studies including laboratoryand field approaches on damage to amphibians from UVB exposure.Field studies in which embryos were exposed to natural sunlightor sunlight with UVB removed have shown conflicting results:some show increased embryonic mortality after UVB exposure,whereas others show that current levels of UVB are not detrimentalto amphibian embryos. The abiotic factors such as water depth,water color, and dissolved organic content of aquatic ovipositionsites effectively reduces UVB penetration through water andreduces exposure to UVB of all life history stages. Biotic factorssuch as jelly capsules around eggs, melanin pigmentation ofeggs, and color of larvae and metamorphosed forms further reduceeffectiveness of UVB penetration. We suggest areas of futureresearch to test the hypothesis of the causal connection betweencurrent UVB levels and amphibian decline.