Article

Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape

Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 05/2010; 107(21):9701-6. DOI: 10.1073/pnas.0912970107
Source: PubMed

ABSTRACT

Increasing UV-B radiation (UV-B; 290-320 nm) due to stratospheric ozone depletion has been a leading explanation for the decline in amphibians for nearly 2 decades. Yet, the likelihood that UV-B can influence amphibians at the large spatial scales relevant to population declines has not yet been evaluated. A key limitation has been in relating results from individual sites to the effect of UV-B for populations distributed across heterogeneous landscapes. We measured critical embryonic exposures to UV-B for two species of montane amphibians with contrasting physiological sensitivities, long-toed salamander (Ambystoma macrodactylum) and Cascades frog (Rana cascadae), at field sites spanning a gradient of UV-B attenuation in water. We then used these experimental results to estimate the proportion of embryos exposed to harmful UV-B across a large number of breeding sites. By combining surveys of the incubation timing, incident UV-B, optical transparency of water, and oviposition depth and light exposure of embryos at each site, we present a comprehensive assessment of the risk posed by UV-B for montane amphibians of the Pacific Northwest. We found that only 1.1% of A. macrodactylum and no R. cascadae embryos across a landscape of breeding sites are exposed to UV-B exceeding lethal levels. These results emphasize that accurately estimating the risk posed by environmental stressors requires placing experimental results in a broader ecological context that accounts for the heterogeneity experienced by populations distributed across natural landscapes.

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    • "Therefore, apoptosis works to secure genomic integrity, avoiding the segregation of the UV-affected chromosome by the elimination of damaged cells (Rastogi et al., 2010). Furthermore, choosing of oviposition sites protected from sunlight helps to reduce the exposure of embryos to UV levels below the lethal dose, thus reducing considerably the environmental risk imposed by solar UVB radiation (Palen and Schindler, 2010). This fact is reinforced by work showing that species that lay their eggs in places protected from sunlight are naturally more susceptible to UVB radiation than species that deposit the embryos on the water surface (Blaustein and Belden, 2003; Häder et al., 2007). "
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    • "One of the first studies to link physiological tolerances to behavior in a field environment revealed that because of parental oviposition behavior, the embryos of the most UV-sensitive species experienced the least UV-B radiation (Palen et al. 2005). Palen and Schindler (2010) combined surveys of the incubation timing, incident UV-B, optical transparency of water, and oviposition depth and light exposure of embryos at various sites to further reveal that exposure to lethal levels of UV-B was minimal in a natural heterogeneous landscape. Collectively, these studies suggest that maintenance of natural heterogeneous habitats is essential for providing opportunities for amphibians to avoid UV-B. "
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