Survival, the hormonal stress response and UV-B avoidance in Cascades Frog tadpoles ( Rana cascadae ) exposed to UV-B radiation

1. Despite the increasing occurrence of global environmental changes, including increases in ultraviolet-B radiation (UV-B; 280–320 nm), little is known about how factors such as UV-B affect animals physiologically. Amphibians provide a good model for examining physiological effects of UV-B exposure because studies documenting both lethal and sub-lethal effects have been completed on many species. 2. This study examines survival and the hormonal stress response, as measured by whole body levels of the glucocorticoid hormone corticosterone, of Cascades Frog, Rana cascadae , tadpoles exposed to ambient UV-B in the field for either 7 or 42 days. 3. There were no differences in corticosterone levels between UV-B exposed and nonexposed tadpoles at either time point. However, after 42 days, survival was significantly higher in tadpoles shielded from UV-B. 4. A stress response profile performed in the field demonstrated that young R. cascadae tadpoles are able to respond to confinement stress with increasing corticosterone. In addition, results from UV-B avoidance tests suggest that R. cascadae tadpoles do not avoid UV-B. 5. Thus, R. cascadae tadpoles may not perceive UV-B radiation, which would explain why they do not respond hormonally to exposure, despite the potential for exposure to result in mortality.