Amphibians have suffered major population declines and extinctions worldwide with climate change and infectious disease the two leading candidates as likely causes. One theory associated with climate change suggests that increases in ultraviolet B radiation, due to ozone depletion, has had a negative impact on amphibian survival. Several studies have confirmed the sensitivity of larval amphibians to UVB, demonstrating both lethal and sublethal effects.

The detrimental effects of UVB on biological systems result from direct mutation in DNA. UVB induces adjacent thymine nucleotides to bond, distorting the DNA molecule blocking transcription and translation, leading to cell death or mutation. Many organisms have a specialised repair mechanism for UVB induced DNA damage, mediated by the enzyme photolyase. Photolyase acts to return the dimer back to the constituent nucleotides restoring the integrity of the DNA moleclule along with cellular processes.

Temperature could influce the effects of UVB on amphibians in two ways. First we might expect repair of DNA damage to be greater at warmer temperatures due to its dependence on enzymatic action. Secondly we could expect the effects on larval development to be reduced at warmer temperatures due to accelerated development reducing exposure time as larvae. Both of these mechanisms suggest that the effects of UVB will be exacerbated at low temperatures. We determined the thermal dependence of UVB effects on embryonic and larval striped marsh frogs Limnodynastes peronii. We reared embryos and larvae under low and high UVB exposure at both 20 and 30 degrees C. Exposure to high UVB reduced hatching success and retarded larval growth in L. peronii, and also reduced swimming performance and survival. These effects were greater at 20 than 30 degrees C providing strong support for our hypothesis. Our data provide some explanation as to the patterns of declines that are seen in the wild. Populations at high altitude (typically cooler climates) seem to have been hit hardest while lowland populations remain largely untouched. Our data further implicate increased UVB in amphibian population declines.