Effect of exposure of ultraviolet B radiation on two anuran species, Polypedates cruciger and Duttaphrynus melanostictus under empirical conditions

Abstract

Increase in ultraviolet (UV)-B radiation has been identified as a suspect in amphibian deformities and decline. Eggs of two amphibian species, Polypedates cruciger and Duttaphrynus melanostictus were exposed to UV-B radiation (312 nm) to receive erythemal dose (0.08 relative response) of the action spectra under laboratory conditions. Biologically estimated doses were calculated to match 50% (high), 25% (medium) and 10% (low) of the average daily irradiance given for the Asian region (17.92 × 10 -3 Wm -2). Hatching success of the eggs and survival, growth of tadpoles and development of malformations were recorded until metamorphosis. Although the exposure had no effect on the hatching success of the eggs of the two species, the survival of tadpoles of both species was significantly reduced compared to the tadpoles coming from unexposed eggs in the control. Tadpoles of both species experienced growth retardations due to UV-B exposure. Exposed individuals were smaller at metamorphosis and they took longer to metamorphose. In addition, malformations such as ulcers, edemas, abnormally pigmented skin were common among the exposed tadpoles. Species-specific differences in the growth were observed between D. melanostictus and P. cruciger but not in the other measured parameters. This study shows that the two anuran species are highly sensitive to levels of UV-B radiation that is present in their natural environment and suffered both lethal and sub-lethal effects.