UV-B Induced Skin Darkening in Larval Salamanders Does Not Prevent Sublethal Effects of Exposure on Growth

Interspecific differences in sensitivity to ultraviolet-B radiation (UV-B; 280–315 nm) are well documented for amphibians. However, few studies have addressed physiological mechanisms underlying differential species survival to such exposure. One potential mechanism that might protect amphibians from damaging UV-B involves melanin production and resultant skin darkening. In this study, we examined (1) the darkening response in salamander larvae exposed to UV-B and (2) whether darker larvae have a higher survival rate than lighter larvae when exposed to UVB. After five days of relatively low UV-B exposure in the laboratory, larval roughskin newts, Taricha granulosa, and Northwestern salamanders, Ambystoma gracile, showed a significant darkening of the skin, as compared to controls exposed to full-spectrum lighting without UV-B. In addition, long-toed salamanders, Ambystoma macrodactylum, showed the same trend for darkening, although it was not statistically significant. To investigate whether survival might be higher for darker larvae exposed to UV-B, we manipulated the skin color of A. gracile and A. macrodactylum larvae by placing them on black or white backgrounds during UV-B exposure. Larvae exposed to UV-B were smaller after three weeks, regardless of background coloration. Background coloration effectively controlled skin color, with larvae on white backgrounds consistently lighter than larvae on black backgrounds. No survival differences were observed between treatments; thus, it remains unclear whether skin darkening provides protection from UV-B damage.