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


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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Available from: Daniel E Schindler
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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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    ABSTRACT: The increased incidence of solar ultraviolet B (UVB) radiation has been proposed as an environmental stressor, which may help to explain the enigmatic decline of amphibian populations worldwide. Despite growing knowledge regarding the UV-induced biological effects in several amphibian models, little is known about the efficacy of DNA repair pathways. In addition, little attention has been given to the interplay between these molecular mechanisms with other physiological strategies that avoid the damage induced by sunlight. Here, DNA lesions induced by environmental doses of solar UVB and UVA radiation were detected in genomic DNA samples of treefrog tadpoles (Hypsiboas pulchellus) and their DNA repair activity was evaluated. These data were complemented by monitoring the induction of apoptosis in blood cells and tadpole survival. Furthermore, the tadpoles' ability to perceive and escape from UV wavelengths was evaluated as an additional strategy of photoprotection. The results show that tadpoles are very sensitive to UVB light, which could be explained by the slow DNA repair rates for both cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6,4) pyrimidone photoproducts (6,4PPs). However, they were resistant to UVA, probably as a result of the activation of photolyases during UVA irradiation. Surprisingly, a sensory mechanism that triggers their escape from UVB and UVA light avoids the generation of DNA damage and helps to maintain the genomic integrity. This work demonstrates the genotoxic impact of both UVB and UVA radiation on tadpoles and emphasizes the importance of the interplay between molecular and sensory mechanisms to minimize the damage caused by sunlight.
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    • "The attenuation of global amphibian populations has become a serious problem worldwide. The decline in the number of amphibian species has been widely reported (Palen and Schindlerb, 2010; Stuart et al., 2004) and it has a major impact on other biological organisms because amphibians are an important part of the ecosystem (Wu and Li, 2004). In vitro studies have shown that spermatogenic Sertoli cells of Rana nigromaculata treated with 1 µg/L MC-LR shows typical ultrastructural changes such as swelling of the mitochondria and endoplasmic reticulum which are associated with necrosis (Zhang et al., 2013). "
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    ABSTRACT: The worldwide occurrence of cyanobacterial blooms due to water eutrophication evokes extreme concerns. These blooms produce cyanotoxins which are hazardous to living organisms. So far among these toxins, Microcystin-LR (MC-LR) is the most toxic and the most frequently encountered toxin produced by the cyanobacteria in the contaminated aquatic environment. Microcystin-LR is a potential carcinogen for animals and humans, and the International Agency for Research on Cancer has classified Microcystin-LR as a possible human carcinogen. After liver, testis has been considered as one of the most important target organs of Microcystin-LR toxicity. Microcystin-LR crosses the blood-testis barrier and interferes with DNA damage repair pathway and also increases expression of the proto-oncogenes, genes involved in the response to DNA damage, cell cycle arrest, and apoptosis in testis. Toxicity of MC-LR disrupts the motility and morphology of sperm and also affects the hormone levels of male reproductive system. MC-LR treated mice exhibit oxidative stress in testis through the alteration of antioxidant enzyme activity and also affect the histopathology of male reproductive system. In the present review, an attempt has been made to comprehensively address the impact of MC-LR toxicity on testis.
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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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