Declines and extinctions of amphibians in well-protected habitats suggest that global atmospheric factors may be responsible. We tested effects of field exposures of ultraviolet radiation (UV-B) on embryo hatching success and time to hatching in three anurans that inhabit high elevation areas of the Sierra Nevada in California, USA. While few obvious environmental impacts have occurred in the high elevation area of the Sierra Nevada, two of the three most common anurans, the Yosemite Toad (Bufo canorus) and the Southern Mountain Yellow-legged Frog (Rana muscosa), have suffered severe population declines while the sympatric Pacific Treefrog (Pseudacris regilla) has remained relatively abundant. Previous studies have shown that hatching of P. regilla embryos at lower elevations are not affected negatively by UV-B radiation. We hypothesized that differences in UV sensitivity may help explain why P. regilla remain abundant while B. canorus and R. muscosa have declined sharply. We conducted field experiments at two remote sites above 3030 m elevation over two years. No effect of UV-B was found on hatching success or rate of development in embryos of B. canorus, P. regilla, or R. muscosa, except for a small, context-dependent increase in time to hatching in R. muscosa. We recommend that research efforts on these species in the Sierra Nevada concentrate on post-hatching effects of UV-B, or on other decline hypotheses.
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Vol. 2010 • No. 3