Changes in the Distribution of "Acris crepitans blanchardi", with Studies of Nesting Microhabitat and the Possible Impact of Ultraviolet-B Radiation

Abstract

Field surveys were completed to determine the current distribution of "Acris crepitans blanchardi" (cricket frog) in lowa, Minnesota, and South Dakota. These field surveys were unable to locate any populations of cricket frogs in Minnesota, South Dakota, or the northernmost tier of lowa counties. This suggests that the range of the cricket frog has been reduced by approximately seventy miles from its northern extreme. The possible impact of ultraviolet (UV) radiation was tested on six species of amphibian eggs as a possible cause for this decline. These included "Acris crepitans", "Ambystoma", "Bufo americanus", "Hyla versicolor complex", "Pseudacris triseriata", and "Rana pipiens". The eggs were subjected to three different light treatments, allowing full transmittance of light, blocking out UV-B and lower wavelengths, and blocking out lower than UV-B wavelengths. "Acris crepitans", "Ambystoma", and "Rana pipiens" showed significantly greater susceptibility to these light treatments. Four factors contribute to radiation-linked destruction of cricket frog eggs. They are among the most susceptible to UV radiation. They are unprotected by large egg masses, egg sheaths, or pigment. They are laid closer to the water surface than other species studied. Finally, they are laid later in the year and are therefore exposed to a longer period of solar radiation than are the other frogs.