A. R. Blaustein1, Peter D. Hoffman1, D. Grant Hokit1, Joseph M. Kiesecker1, Susan C. Walls1, J B Hays1
1Department of Zoology, Oregon State University,
Corvallis 97331.
Tóm tắt
The populations of many amphibian species, in
widely scattered habitats, appear to be in severe decline; other amphibians show
no such declines. There is no known single cause for the declines, but their
widespread distribution suggests involvement of global agents--increased UV-B
radiation, for example. We addressed the hypothesis that differential
sensitivity among species to UV radiation contributes to these population
declines. We focused on species-specific differences in the abilities of eggs to
repair UV radiation damage to DNA and differential hatching success of embryos
exposed to solar radiation at natural oviposition sites. Quantitative
comparisons of activities of a key UV-damage-specific repair enzyme, photolyase,
among oocytes and eggs from 10 amphibian species were reproducibly
characteristic for a given species but varied > 80-fold among the species.
Levels of photolyase generally correlated with expected exposure of eggs to
sunlight. Among the frog and toad species studied, the highest activity was
shown by the Pacific treefrog (Hyla regilla), whose populations are not known to
be in decline. The Western toad (Bufo boreas) and the Cascades frog (Rana
cascadae), whose populations have declined markedly, showed significantly lower
photolyase levels. In field experiments, the hatching success of embryos exposed
to UV radiation was significantly greater in H. regilla than in R. cascadae and
B. boreas. Moreover, in R. cascadae and B. boreas, hatching success was greater
in regimes shielded from UV radiation compared with regimes that allowed UV
radiation. These observations are thus consistent with the UV-sensitivity
hypothesis.
