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Although considerable research has addressed effects of elevated ultraviolet-B (UV-8) radiation on vegetative plant structures and processes, the reproductive biology and patterns of inheritance of UV-B tolerance have received much less attention. I examined the effects of UV-B radiation on pollen of 34 taxa. I also addressed questions concerning the patterns of inheritance of UV-B tolerance in Arabidopsis thaliana and examined potential cumulative carryover effects of UV-B exposure through multiple generations of this species. In the first study, a significant reduction in pollen germination occurred in only five species, but pollen tube growth in more than half of the species exhibited significant reductions . Proportionate to their numbers in this survey of 34 taxa: Monocotyledonous species were more sensitive to UV-8 than the dicotyledonous species, wild species were more sensitive than cultivated species, and pollen from plants growing in the field was somewhat more sensitive than pollen from plants grown in the greenhouse. The results also suggested a possible adaptation to UV-8 radiation during the course of the season. The second study probed patterns of inheritance of UV-8 tolerance. General combining ability and specific combining ability were both significant for several traits in Arabidopsis. This suggests that plant breeders may develop UV-8 tolerant strains of plant species both in the form of pure lines and hybrids. In the third experiment, I found that a significant carryover effect of UV-B exposure through multiple generations Arabidopsis thaliana was evident in a subsequent generation, in either the presence or absence of UV-B, once differences in the reactions of different ecotypes were taken into account. However, instead of an expected accumulation of UV-B effect as a greater number of generations were exposed to the radiation, there was an apparent reversion of the cumulative, carryover effect. This was evident in that plants exposed to seven generations of UV-B exhibited much less carryover effect than did plants exposed for only three generations.

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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. / Graduation date: 2012