Do effects of mercury in larval amphibians persist after metamorphosis?
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Despite widespread concern about the role of environmental contaminants in global amphibian declines, and evidence that post-metamorphic life stages contribute disproportionately to amphibian population dynamics, most studies in amphibian ecotoxicology focus on larval life stages. Studies that focus solely on early life stages may miss important effects of contaminant exposure, such as latent effects that manifest some time after previous exposure. Moreover, it is often assumed that effects observed in amphibian larvae will persist to affect survival or reproduction later in life. We used terrestrial enclosures to determine whether exposure to mercury (Hg) through maternal transfer and/or larval diet had any adverse effects in post-metamorphic American toads (Bufo americanus). We found a 5% difference in size at metamorphosis that was attributed to maternal Hg exposure persisted for 1 year in the terrestrial environment, resulting in a 7% difference at the conclusion of the study. Although patterns of survival differed among treatments through time, we found no overall difference in survival after 1 year. We also found no evidence of emergent latent effects in the terrestrial toads that could be attributed to earlier exposure. Our results indicate that adverse effects of maternal Hg exposure that were observed in larval amphibians may persist to affect later terrestrial life stages but that no novel adverse effects developed when animals were raised in a semi-natural environment. Moreover, we found no evidence of persistent effects of dietary Hg exposure in larvae, highlighting a need for greater focus on maternal effects in amphibian ecotoxicology. Finally, we suggest an increase in the use of longitudinal studies to better understand contaminant impacts to amphibian populations via effects in both aquatic and terrestrial life stages.
KeywordsAmphibian declines Carryover effects Latent effects Maternal effects Population models
We thank the landowners long the South River and the Waynesboro Parks and Recreation Department for access to sampling locations, J. Schmerfeld, D. Cristol, K. Carlson-Drexler, A. Condon, M. Howie, C. Ramos, J. Burke, J. Callihan, S. DuRant, M.K. McCaleb, J. McPherson, and H. Wada for their support, field and/or laboratory assistance, and C. Shade of Quicksilver Scientific for MMHg analysis. Collection of animals was in conformance with appropriate permits, and sample methods were in compliance with Virginia Polytechnic and State University’s animal care and use protocols. Financial support was provided by E. I. DuPont de Nemours, the National Science Foundation (NSF # IOB-0615361), and a US EPA STAR Graduate Fellowship (FP-9170040-1) to CMB. EPA has not officially endorsed this publication and the views expressed herein may not reflect the views of the EPA. Research was completed with oversight from the South River Science Team which is a collaboration of state and federal agencies, academic institutions, and environmental interests.
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