Blaustein A R, Hoffman P D, Hokit D G, Kiesecker J M, Walls S C, Hays J B
Department of Zoology, Oregon State University, Corvallis 97331.
Proc Natl Acad Sci U S A. 1994 Mar 1;91(5):1791-5. doi: 10.1073/pnas.91.5.1791.
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.
许多两栖动物物种分布在广泛分散的栖息地，其种群数量似乎在急剧下降；而其他两栖动物则没有出现这种下降情况。目前尚不清楚导致种群数量下降的单一原因，但它们分布广泛这一情况表明可能涉及全球因素，例如紫外线B辐射增加。我们探讨了物种对紫外线辐射的不同敏感性导致这些种群数量下降的假设。我们重点研究了不同物种的卵修复紫外线对DNA造成损伤的能力差异，以及在自然产卵地暴露于太阳辐射下的胚胎孵化成功率差异。对10种两栖动物的卵母细胞和卵中一种关键的紫外线损伤特异性修复酶——光解酶的活性进行定量比较，结果表明，对于给定物种，其活性具有可重复性特征，但不同物种之间的活性差异超过80倍。光解酶的水平通常与卵预期接受的阳光照射量相关。在所研究的青蛙和蟾蜍物种中，太平洋树蛙（雨蛙属）的光解酶活性最高，其种群数量目前尚未出现下降。种群数量显著下降的西部蟾蜍（北美蟾蜍）和喀斯喀特蛙（喀斯喀特林蛙）的光解酶水平则明显较低。在野外实验中，暴露于紫外线辐射下的雨蛙属胚胎的孵化成功率显著高于喀斯喀特林蛙和北美蟾蜍。此外，与允许紫外线辐射的环境相比，在免受紫外线辐射的环境中，喀斯喀特林蛙和北美蟾蜍的孵化成功率更高。因此，这些观察结果与紫外线敏感性假设一致。
