Effects of selenium exposure on the hematology, innate immunity, and metabolic rate of yellow-bellied sliders (Trachemys scripta scripta)

Abstract

Selenium (Se) is a naturally occurring essential element that can be toxic to vertebrates at high concentrations. Despite studies that have documented that wild reptile species can accumulate copious amounts of Se, little is known regarding specific toxicologic effects of Se. In this study, 70 juvenile yellow-bellied sliders (Trachemys scripta scripta) were exposed to one of three seleno-L-methionine (SetMet) treatments (control, n = 24; 15 mg/kg, n = 23; and 30 mg/kg, n = 23) via weekly oral gavage for 5 weeks. At the conclusion of the experiment, kidney, liver, muscle, and blood samples were collected for quantitative Se analysis. Turtles in the SeMet treatment groups accumulated significantly higher amounts of Se in all tissue types relative to controls (all p < 0.001). Turtles in the 30 mg/kg SeMet group also accumulated significantly higher amounts of Se compared to the 15 mg/kg group (all p < 0.001). Although toxicity thresholds for reptiles have not been established, Se concentrations in liver tissue from both SeMet treatment groups exceeded reported avian toxicity thresholds for liver tissue. Neither oxygen consumption nor innate bactericidal capacity were impacted by SeMet exposure. However, turtles in the 30 mg/kg SeMet group exhibited anemia, which has been reported in other vertebrates exposed to Se. Furthermore, juvenile T. s. scripta in the 30 mg/kg SeMet group experienced 17% mortality compared to 0% in the 15 mg/kg treatment and control groups. To our knowledge, this study is the first to report dose-dependent Se-associated anemia and mortality in a chelonian species.

Effects of 2 Neonicotinoid Insecticides on Blood Cell Profiles and Corticosterone Concentrations of Wood Frogs ( Lithobates sylvaticus )

“…caused by chronic infections, exposure to toxins, nutritional deficiency, or damage to or inflammation of the liver or kidney, which are important sites of erythropoiesis in young amphibians (Grimes and Fry 2015). Chronic anemia can be detrimental in wild amphibians because the reduction in oxygen and carbon dioxide-carrying capacities can result in tissue damage, decreased fitness, and increased stress (Haskins et al 2017). It is unlikely that the anemia was a consequence of husbandry-related malnourishment (Cital and Goodnight 2016), given that this was only seen in the treatment, and not the control animals.…”

Experimentally Induced Selenosis in Yellow-Bellied Slider Turtles (Trachemys scripta scripta)

“…2,6 In the summer of 2015, we exposed slider turtles to selenium to examine its impact on their hematology, immune response, and metabolism. 10 Because we observed signs indicative of selenosis, we collected samples for histologic analysis to determine if selenium exposure caused changes in turtle tissues. Overall, the objective of this study was to determine if histologic changes occur in tissues from yellow-bellied slider turtles associated with experimentally induced selenosis.…”

“…In our primary experiment, slider turtles treated with the highest dose of SeMet exhibited multiple signs of selenosis, including negative hematologic effects (eg, reduced lymphocyte counts, increased heterophil counts, and hemolytic anemia), sloughing of claws, and mortality. 10 Selenium-treated turtles from which tissues were collected for histopathology all had tissue selenium levels that surpassed "level of concern" thresholds established for avian species. 10 10 All 4 tissues examined had changes that were either not seen in the controls (claw and kidney) or were more severe than in the controls (muscle and liver) ( Table 1).…”

“…10 Selenium-treated turtles from which tissues were collected for histopathology all had tissue selenium levels that surpassed "level of concern" thresholds established for avian species. 10 10 All 4 tissues examined had changes that were either not seen in the controls (claw and kidney) or were more severe than in the controls (muscle and liver) ( Table 1).…”

“…Selenium blood and liver content in our sliders from this study are comparable with levels found in wild sliders in coal-contaminated environments. 10 However, more research is needed to determine if exposure in the wild results in similar histopathologic abnormalities in slider turtles. Figure 6.…”