Abstract
The synthetic 17α-ethinylestradiol (EE2) is a common estrogenic pollutant that has been suspected to affect the demography of river-dwelling salmonids. One possibility is that exposure to EE2 tips the balance during initial steps of sex differentiation, so that male genotypes show female-specific gene expression and gonad formation. Here we study EE2 effects on gene expression around the onset of sex differentiation in a population of European grayling (Thymallus thymallus) that suffers from sex ratio distortions. We exposed singly-raised embryos to one dose of 1 ng/L EE2, studied gene expression 10 days before hatching, at the day of hatching, and around the end of the yolk-sac stage, and related it to genetic sex (sdY genotype). We found that exposure to EE2 affects expression of a large number of genes, especially around hatching. These effects were strongly sex-dependent. We then raised fish for several months after hatching and found no evidence of sex reversal in the EE2-exposed fish. We conclude that ecologically relevant (i.e. low) levels of EE2 pollution do not cause sex reversal by simply tipping the balance at early stages of sex differentiation, but that they interfere with sex-specific gene expression.
Highlights
Endocrine-disrupting chemicals are common pollutants that typically enter the environment after wastewater treatment
Genetic males displayed no significantly altered expression at a false discovery rate (FDR) of 15%; yet there was a weak signal of expression change for more than 10,000 genes at 25% FDR (Table 1b, Additional file 1: Figure S5c and Table S2)
From what is known about possible EE2 effects on fish in general, we expected that this common pollutant may (i) affect sex determination of grayling by influencing the few initial triggers that start the canalized developmental process of gonad formation, and (ii) be toxic to the embryos and juveniles because it interferes with different types of physiological processes, especially those that are endocrinologically regulated
Summary
Endocrine-disrupting chemicals are common pollutants that typically enter the environment after wastewater treatment. One of the most potent of these pollutants is the synthetic 17-alpha-ethinylestradiol (EE2) that is used in oral contraceptives and hormone replacement therapies, and that is more stable and persistent than the natural estrogen it mimics [1]. EE2 concentrations of 1 ng/L and higher have been found in river or lake surface waters [2], in lake sediments [3], and even in groundwater [4]. Concentrations around 1 ng/L have ecological relevance. Exposure to 1 or a few ng/L EE2 can be damaging to fish at various developmental stages. Embryos and early larvae can suffer from increased mortality, reduced
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