A comparison of the photolyase activity of three Australian tree frogs

Ultraviolet-B (UV-B) irradiation of DNA generates mutagenic photoproducts such as cyclobutane pyrimidine dimers (CPDs) which can affect the growth and development of amphibian embryos. Differential ability to repair UV-B-induced DNA damage may be responsible for differences in population stability between some amphibian species. Photoreactivation via the enzyme photolyase is a major mechanism used to remove CPDs from DNA. The aim of this study was to determine if photolyase activity differed in three sympatric Australian amphibian species; one of which has suffered marked population declines (Litoria aurea) and two whose populations do not appear to be in decline (L. dentata and L. peronii). The specific activity of photolyase was measured in each species, and compared to the hatching success of eggs of these species under unfiltered summer sunlight. The mean specific activities of photolyase were 1.10 ± 0.18 x 10¹¹, 5.76 ± 1.01 x 10¹¹, and 2.66 ± 0.15 x 10¹¹ CPDs repaired per hour per µg of egg protein extract, for L. aurea, L. dentata and L. peronii, respectively. When intrinsic differences in hatching success between species were controlled for, the relative percentage hatching success under unfiltered sunlight of L. aurea (77%) was lower than that of L. peronii (91%) and L. dentata (98%), however, these values did not differ significantly. Litoria aurea had the lowest photolyase activity of the three species and showed a non-significant trend of reduced hatching success under UV-B exposure.