Effects of atrazine on anuran development are altered by the presence of a nonlethal predator.

Although predator-induced stress is a common biotic factor in aquatic communities that can strongly influence anuran development, there have been no studies to date that examined the interaction between this factor and atrazine, the most widely used pesticide in the United States. The potential synergistic effects of atrazine (0, 20, or 200 microg/L) and predatory stress on the survival, growth, development, and reproductive development of Hyla versicolor (gray treefrog) tadpoles were investigated. Atrazine reduced the proportion of tadpoles reaching metamorphosis; however, this effect was modified by the presence of a nonlethal predator. The combined effects of predatory stress and exposure to 200 microg/L atrazine resulted in the lowest proportion of tadpoles reaching metamorphosis. No treatment effects were observed for mass, snout-urostyle length, or the proportion of metamorphs that were male or female. No macroscopic gonadal anomalies were observed. Many gonads were underdeveloped; however, gonadal development was more advanced in metamorphs exposed to 200 microg/L atrazine. This effect was modified by the presence of a nonlethal predator such that female gonadal development was further accelerated and male gonadal development was retarded by predatory stress. These results indicate that simplified laboratory studies may not accurately reflect the effects of atrazine on anuran development in natural communities.