Beschreibung:
<p>Heightened concern over endocrine-disrupting chemicals is driven by the hypothesis that they could reduce reproductive success and affect wildlife populations, but there is little evidence for this expectation. The pharmaceutical ethynylestradiol ( EE<sub>2</sub>) is a potent endocrine modulator and is present in the aquatic environment at biologically active concentrations. To investigate impacts on reproductive success and mechanisms of disruption, we exposed breeding populations (n = 12) of zebrafish (Danio rerio) over multiple generations to environmentally relevant concentrations of EE<sub>2</sub>. Life-long exposure to 5 ng/ L EE<sub>2</sub>in the F<sub>1</sub>generation caused a 56% reduction in fecundity and complete population failure with no fertilization. Conversely, the same level of exposure for up to 40 days in mature adults in the parental F<sub>0</sub>generation had no impact on reproductive success. Infertility in the F<sub>1</sub>generation after life-long exposure to 5 ng/ L EE<sub>2</sub>was due to disturbed sexual differentiation, with males having no functional testes and either undifferentiated or intersex gonads. These F<sub>1</sub>males also showed a reduced vitellogenic response when compared with F<sub>0</sub>males, indicating an acclimation to EE<sub>2</sub>exposure. Depuration studies found only a partial recovery in reproductive capacity after 5 months. Significantly, even though the F<sub>1</sub>males lacked functional testes, they showed male-pattern reproductive behavior, inducing the spawning act and competing with healthy males to disrupt fertilization. Endocrine disruption is therefore likely to affect breeding dynamics and reproductive success in group-spawning fish. Our findings raise major concerns about the population-level impacts for wildlife of long-term exposure to low concentrations of estrogenic endocrine disruptors.</p>