Selenium:Mercury Molar Ratios in Bullfrog and Leopard Frog Tadpoles from the Northeastern United States

Abstract

Vertebrates experience adverse effects from methylmercury, largely obtained through their food. Selenium has the potential to reduce the toxic effects of methylmercury (and vice versa). In this paper, we examine the selenium:mercury molar ratios in tadpoles (Lithobates sphenocephalus, Lithobates catesbeianus (formerly Rana), and a newly documented leopard frog species currently referred to as R. sp. nov.) and fully formed leopard frog metamorphs. There were no significant differences in metal levels between the two leopard frog species, and data were therefore combined. Selenium:mercury molar ratios varied from 19 to 38 for bullfrog tadpoles, from 16 to 330 for leopard frog tadpoles, and from 7 to 17 for leopard frog metamorphs. Leopard frog tadpoles with less than 45 days exposure to field conditions had significantly higher molar ratios than other tadpoles and leopard frog metamorphs. There were significant locational differences for the molar ratios of bullfrogs, and leopard frog tadpoles with more than 45 days of field exposure. At the sites where we were able to sample both leopard frog tadpoles and leopard frog metamorphs, there were significant differences between the two distinct life stages. Most of the variation in the ratio was accounted for by selenium levels, field sites, and exposure period.

Cryptic Diversity in Metropolis: Confirmation of a New Leopard Frog Species (Anura: Ranidae) from New York City and Surrounding Atlantic Coast Regions

“…Others, however, occurred enigmatically within less-developed coastal, suburban, and semi-rural areas ( Fig. 1 ); this includes Long Island [3] , [13] , the largest island in the continental US and a former leopard frog stronghold [10] where potential causes of extirpations (e.g., disease, invasive species, and contaminants) are being assessed [83] (J. A. Feinberg and J. Burger, unpublished data).…”

Survey of mercury in boreal chorus frog (Pseudacris maculata) and wood frog (Rana sylvatica) tadpoles from wetland ponds in the Prairie Pothole Region of Canada

“…Differences in Hg concentration in the ponds were apparent for both species of tadpoles, suggesting that Hg concentration in algae and lower trophic organisms must also have been elevated because diet is the main vector of Hg in most vertebrates (Burger et al 2014). Another explanation of high values in certain ponds is that the gastrointestinal tracts (GT) of tadpoles sampled from the high Hg ponds contained sediment with an elevated Hg concentration.…”