Reduced Fitness of Daphnia magna Fed a Bt-Transgenic Maize Variety

Abstract

Genetically modified (GM) maize expressing the Bt-toxin Cry1Ab (Bt-maize) was tested for effects on survival, growth, and reproduction of the water flea Daphnia magna, a crustacean arthropod commonly used as a model organism in ecotoxicological studies. In three repeated experiments, D. magna were fed 100% ground maize in suspension, using either GM or isogenic unmodified (UM) maize. D. magna fed GM-maize showed a significantly reduced fitness performance: The mortality was higher, a lower proportion of females reached sexual maturation, and the overall egg production was lower compared to D. magna fed UM isogenic maize. We conclude that the tested variety of Bt-maize and its UM counterpart do not have the same quality as food sources for this widely used model organism. The combination of a reduced fitness performance combined with earlier onset of reproduction of D. magna fed Bt-maize indicates a toxic effect rather than a lower nutritional value of the GMmaize.

Chronic Responses ofDaphnia magnaUnder Dietary Exposure to Leaves of a Transgenic (Event MON810) Bt–Maize Hybrid and its Conventional Near-Isoline

“…In contrast with these results, Bøhn et al (2008) observed an earlier onset of reproduction and reduced survival in D. magna fed MON810 Bt-maize kernels of a different hybrid, suggesting a weak adverse effect of rCry1Ab, for which the concentration was approximately 30-fold lower than in leaf feed used in this study. This apparent discrepancy seems to indicate the absence of a toxic effect of the MON810 rCry1Ab in D. magna, but one needs to bear in mind that the influence of rCry1Ab (or any other toxin) might be modulated by food quantity and quality (Heugens et al, 2006;Chandini, 1989).…”

“…This includes (i) delayed reproduction and reduced clutch size and total fecundity at low toxin concentrations, with additional negative effects on body size and survival at high toxin concentrations (Villarroel et al, 2003;Heugens et al, 2006); (ii) severely impaired growth, reproduction, and survival (high toxicity); and (iii) early-life fecundity compensation at the expense of later growth and survival (low toxicity) (Bøhn et al, 2008).…”

“…2. The truncated, readily active rCry1Ab toxin expressed in MON810 maize and/ or the detected rCry1Ab-related proteins/ fragments (the existence of which in fact constitutes unintended effects) might exert a low toxic effect in D. magna (Bøhn et al, 2008), through an as yet unknown mode of action. In addition, inside MON810 maize, rCry1Ab may undergo posttranslational modifications that otherwise would not happen in bacteria, and thus also influence toxicity (Franck-Oberaspach and Keller, 1997).…”

“…In contrast, negative nontarget effects of Bt-maize were found in certain cases, particularly for aquatic organisms, such as Trichoptera larvae fed Bt-maize leaves (Rosi-Marshall et al, 2007;Chambers et al, 2010), and Daphnia magna fed ground Bt-maize kernels (Bøhn et al, 2008(Bøhn et al, , 2010. Significant effects of MON810 maize were recently noted in salmon (Salmo salar) (Gu et al 2013(Gu et al , 2014, but were considered to be of minor biological significance because the overall development and health of the animals was not affected.…”

Are Ready for Market Genetically Modified, Conventional and Organic Soybeans Substantially Equivalent as Food and Feed?

“…Previous studies in D. magna D. magna has been used as an ecotoxicological model for testing GM crop plants in short-term studies (Mendelson et al 2003;Raybould and Vlachos 2011) and over the full life-cycle (Bøhn et al 2008), and for testing combinatorial effects of Bt toxins and predation risk (Bøhn et al 2010). Cuhra and co-workers tested chronic effects of glyphosate and Roundup and showed that environmental concentrations of 0.05-0.45 mg/l (active ingredient) cause negative effects on D. magna offspring size and reproduction (Cuhra et al 2013).…”