Elevational differences in UV-B response by the long-toed salamander (Ambystoma macrodactylum) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/w0892d64b

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  • Global amphibian declines have been attributed to numerous and often synergistic causes, such as invasive species, pathogens, and ultraviolet-B (UV-B) radiation. The effects of these stressors are context dependent and can vary with location, species, and populations. As sensitivity to UV-B has shown inconsistencies across amphibian taxa, it can be expected that variation also occurs between populations of a single species. High elevation populations of the long-toed salamander (Ambystoma macrodactylum) face exponentially higher UV-B radiation levels relative to low elevation populations and these levels are predicted to increase in conjunction with continued ozone depletion. We hypothesized that breeding long-toed salamander females at high elevations have modified oviposition behavior to better protect embryos from UV-B induced damage. In addition, we hypothesized that long-toed salamander embryos at high elevation would exhibit elevated photolyase activity, a photo-reactivating enzyme that repairs UV-B radiation-induced damage to DNA. We predicted that this behavioral defense strategy would be employed together with an elevated physiological response as a correlated defense response to increased levels of UV-B radiation in high elevation populations. We surveyed high and low elevation long-toed salamander breeding sites throughout Oregon to quantify oviposition site characteristics and associated UV-B profiles. We simultaneously collected embryos for quantification of photolyase activity in a bacterial transformation assay. We found significant differences in oviposition behavior across elevations, with high elevation breeding females ovipositing in deeper water and using UV-B protective refugia. Oviposition sites at low elevations, however, were most often found in UV-B exposed microhabitats located at the surface of the water. This population difference in oviposition behavior resulted in a standardization of UV-B and temperature conditions for long-toed salamander embryos across elevation. In contrast, we found no population differentiation in photolyase activity between high and low elevation breeding sites. This indicates that behavioral selection for UV-B protected oviposition substrates may either be negating the need for increased photolyase activity in long-toed salamander embryos, or that populations lack the capacity to adapt a heightened physiological response to UV-B at high elevations. Together, these results show how trade-offs in physiology and behavior are a unique adaptation to a significant environmental stressor. Further research into the susceptibility of amphibian species to changing environmental conditions may help to demonstrate the effectiveness of correlated trait responses and plasticity in behavior, and species persistence under changing climate regimes.
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