Graduate Thesis Or Dissertation
 

The lethal response of the roughskin newt, Taricha granulosa (Skilton), to ultraviolet-B radiation at three fluence rates

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  • Roughskin newts, Taricha granulosa (Skilton), were exposed to UV-B (280-320nm), UV-A (321-380 nm), and visible radiation from fluorescent sunlamps (Westinghouse FS40) that were filtered with cellulose acetate film. UV-B controls were exposed to irradiation from sunlamps that were filtered with Mylar-D, a polyester film that effectively absorbed UV-B radiation while allowing the penetration of UV-A and visible wavelengths. UV controls were irradiated with Vita-Lite lamps (Duro-Test Co., North Bergen, NJ) that produce relatively high intensity visible radiation, but only minimal amounts of UV-A and UV-B. The effects of total accumulated UV-B fluences between 300 and 1300 kJm⁻² were examined at three fluence rates (0.337, 0.646, and 1.179 Wm⁻² UV-B). Lethality was found to be a dose-dependent phenomenon that occurred at total accumulated UV-B fluences above a threshold dose of approx. Exposure at all three fluence rates resulted in mortality. Thus, even the lowest fluence rate was above the fluence rate threshold for Taricha. A dose rate effect appears to exist, with respect to LD50 and threshold lethal dose, between the low and intermediate fluence rates. In addition to the lethal effect, UV-B exposure resulted in excessive skin sloughing, blanching, and ulceration of the dorsal skin and the development of a darkly pigmented mid-dorsal stripe in some individuals. At the microscopic level, UV-B irradiated skin showed edematous changes and cytopathology. It is proposed that UV-B induced skin damage in Taricha leads to a deficiency in cutaneous respiration that may ultimately result in death. Other potentially lethal systemic effects, that may result from a breakdown in skin integrity, include infection and osmoregulatory dysfunction.
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