Differential Acute Sensitivity of Wild Rana sylvatica and Laboratory Xenopus laevis Tadpoles to the Herbicide Atrazine

Atrazine is one of the most used herbicides in the United States and has previously been implicated in local amphibian declines. The purpose of this study was to examine the influence of atrazine on 2 frog species-the amphibian model species Xenopus laevis and the wood frog Rana sylvatica. Tadpoles just before hindlimb emergence were exposed to either 1 part per billion (ppb) or 25 ppb atrazine in their water. Behavior was observed daily, and at the end of 15 days exposure the tadpoles were weighed, developmentally staged, and measured for head width and tail width. Differences were found among all of these for the X. laevis (p < 0.002), with the difference occurring only for the low dose animals (and not the high dose animals) for weight, stage, and tail width. Head width was significantly different for the X. laevis exposed to both the high and low concentrations of atrazine. No morphological differences were seen in R. sylvatica, but increased mortality and behavioral differences were seen in the R. sylvatica high dose group. These results suggest that: (1) Xenopus laevis may not be an adequate model for all anurans (2) low doses of atrazine have a greater influence than high doses in X. laevis, and (3) Rana sylvatica is more sensitive in lethal but not sublethal endpoints.