Aquatic and terrestrial stressors in amphibians: a test of the double jeopardy hypothesis based on maternally and trophically derived contaminants.

Amphibians with biphasic life histories occupy aquatic and terrestrial habitats at different times in their lives, leading to a double jeopardy of contaminant risk in both habitats. The present study examines individual and interactive effects of mercury exposure to terrestrial adults and aquatic larvae on fitness-related traits of American toads, Bufo americanus. Eggs from reference mothers or contaminated mothers were allowed to hatch and larvae were fed diets of either no added Hg or 2.5 or 10 µg/g total Hg (dry wt). Both dietary and maternal Hg had adverse effects on developing larvae, but there was no interaction between these factors. Dietary Hg had a marginal effect of decreased survival with increasing Hg in the diet. Animals from Hg-exposed mothers weighed 14% less than those from reference mothers, and size at metamorphosis was directly correlated with hopping performance. Animals from Hg-exposed mothers also took longer to complete metamorphosis and had 2.5 times the prevalence of spinal malformations compared with those from reference mothers. Results of the present study demonstrate that amphibians do indeed face a double jeopardy of contaminant exposure stemming from terrestrial and aquatic environments, because both exposure pathways adversely affected developing offspring. The present study also demonstrates that all possible routes of exposure over an organism's life history must be examined to provide a comprehensive picture of the ecological consequences of habitat contamination.