LAUSR

Standard ecological risk assessment practices often rely on larval and juvenile fish toxicity data as representative of the amphibian aquatic phase. Empirical evidence suggests that endpoints measured in fish early life stage tests are often sufficient to protect larval amphibians. However, the process of amphibian metamorphosis relies on endocrine cues that affect development and morphological restructuring and are not represented by these test endpoints. This study compares developmental endpoints for zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis), two standard test species, exposed to the herbicide trifluralin throughout the larval period. D. rerio were more sensitive and demonstrated a reduction in growth measurements with increasing trifluralin exposure. Size of X. laevis at metamorphosis was not correlated with exposure concentration; however, time to metamorphosis was delayed relative to trifluralin concentration. Gene expression patterns indicate discrepancies in response by D. rerio and X. laevis, and dose-dependent metabolic activity suggests that trifluralin exposure perturbed biological pathways differently within the two species. While many metabolites were correlated with exposure concentration in D. rerio, non-targeted hepatic metabolomics identified a subset of metabolites that exhibited a non-monotonic response to trifluralin exposure in X. laevis. Linking taxonomic distinctions in cellular-level response with ecologically relevant endpoints will refine assumptions used in inter-species extrapolation of standard test effects and improve assessment of sublethal impacts on amphibian populations. This article is protected by copyright. All rights reserved.