Dietary Selenomethionine Administration in the American Alligator (Alligator mississippiensis): Hepatic and Renal Se Accumulation and Its Effects on Growth and Body Condition
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Selenium (Se) is an essential trace nutrient, but in excess, it can induce toxicity. Incomplete combustion of coal produces coal combustion wastes, which are enriched in Se and often disposed of in aquatic basins. While a multitude of studies have investigated Se accumulation in vertebrates, few studies have examined its effects on longer-lived top trophic carnivores, such as the American alligator (Alligator mississippiensis). In this study, alligators were fed one of three Dietary Treatments: mice injected with water (controls) or water supplemented with 1000 or 2000 ppm selenomethionine (SeMet). Dietary Treatment significantly affected Se levels in both the liver (p < 0.0001; raw mean ± SE: 1000 ppm group, 35.20 ± 6.32 ppm; 2000 ppm group, 49.97 ± 4.00 ppm) and kidney (p < 0.0001; raw mean ± SE: 1000 ppm group, 101.60 ± 8.64 ppm; 2000 ppm, 96.38 ± 5.81 ppm), which were significantly higher in alligators fed SeMet than in controls. Post-treatment head length, used to control for size variation, was negatively related to both kidney (p = 0.0142) and liver (p = 0.0010) Se concentrations. Dietary treatment with SeMet significantly reduced body condition (1000 ppm, p < 0.0029; 2000 ppm, p = 0.0075), but it significantly increased growth (1000 ppm, p < 0.0001; 2000 ppm, p = 0.0316). Body condition and growth remained unchanged in control alligators (p > 0.05). Our results demonstrate alligators are capable of accumulating high levels of Se through trophic transfer. The positive effects of accumulation on growth may demonstrate Se essentiality, whereas the negative effects on condition may demonstrate toxicity. Accumulation also was associated with mortality, further demonstrating toxicity. Future studies should further investigate the physiological effects of Se accumulation in long-lived, top-trophic carnivores.
KeywordsDietary Treatment SeMet Control Alligator Coal Combustion Waste Savannah River Site
We would like extend a special thanks to Ruth Elsey and her staff at Rockefeller Wildlife Refuge for providing alligators used in this study. Sharon L. Finger assisted in transport of alligators from LA to SC. William Hopkins (Virginia Tech) provided insight on dosage regimens. John Seaman and his lab at SREL analyzed Se concentrations in blood and tissues. Bess Harris, Nicole White, Nick Bossenbroak (NB), and Caitlin Kupar assisted in feeding. Megan Winzeler, Daniel Quinn, Sam Dean, and David Haskins helped with alligator blood sampling and dissections. NB also assisted with processing samples for digestions and trace element analysis. Meghan D. Kelley helped with statistical analysis. JWF was funded by the Department of Environmental Health Science and the Interdisciplinary Toxicology Program. MTH was funded by a grant from the Area Closures Project to TDT. Support for this work was provided in part by Award No. DE-FC09-07SR22506 from Department of Energy to the University of Georgia Research Foundation. All experimental protocols were approved by the Institutional Animal Care and Use Committee at the University of Georgia (Approval No. A2014 01-030-Y1-A3).
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