The effect of a low iron diet and early life methylmercury exposure in Daphnia pulex

Abstract

Iron (Fe) deficiency increases risk for adverse health outcomes in humans; however little is known about the potential interaction with methylmercury (MeHg) exposure. Studies testing multiple stressor hypotheses are expensive and time consuming in mammalian model systems; therefore, determining relevance of alternative models is important. Daphnia pulex were fed standard or low-Fe diets of freshwater algae, Ankistrodesmus falcatus. MeHgCl (1600 ng/L) or vehicle was added to culture media for 24 h during early life, and the combinatorial effects of a low-Fe diet and MeHg exposure on lifespan, maturation time, and reproduction were evaluated. Lipid storage effects were measured using image analysis of Oil Red O staining and triacylglyceride quantification. Our results show a dose-dependent reduction in lifespan in D. pulex fed low Fe diets. Lipid analysis suggests an interactive effect of diet and MeHg exposure, with MeHg exposure increasing lipid storage in D. pulex fed a low-Fe diet. These findings suggest the effects of dietary iron intake and early life MeHg exposure in D. pulex may be mediated by changes in energetics that result in differential lipid storage. Therefore, lipid storage in D. pulex may be a useful screen for detecting long-term effects of multiple stressors early in life.

Importance of diet in amphibian metamorphosis‐based studies designed to assess the risk of thyroid active substances

“…ranging from daphnids (Demott & Muller-Navarra, 1997;Elendt & Bias, 1990;Gregor et al, 1991;Hudson et al, 2016) to Xenopus (Fort et al, 1999;Fort & Schlekat, 2002). Overall, the present study demonstrated that the SMN benchmark provides a good representation of feeding conditions provided by the natural habitat of X. laevis.…”

“…However, with strict consideration of studies performed in the laboratory, we hypothesize that the slower‐than‐natural rates of metamorphosis in the previously discussed laboratory‐based studies (Balch et al, 2006; Carr et al, 2003; Conners et al, 2009; DuPreez et al, 2008; Goleman et al, 2002; Goleman & Carr, 2006; Hu et al, 2006; Plowman et al, 1994; Sharma & Patiño, 2009) likely resulted from the inadequate nutritional quality of the diet. Historically, nutritional deficiencies in standard laboratory‐based populations have been identified ranging from daphnids (Demott & Muller‐Navarra, 1997; Elendt & Bias, 1990; Gregor et al, 1991; Hudson et al, 2016) to Xenopus (Fort et al, 1999; Fort & Schlekat, 2002). Overall, the present study demonstrated that the SMN benchmark provides a good representation of feeding conditions provided by the natural habitat of X. laevis .…”