Experimental evaluation of vitellogenin as a predictive biomarker for reproductive disruption

Vitellogenin (VTG) synthesis in male oviparous vertebrates is used as an in dicator of environmental estrogen exposure, but the relationship between el evated VTG levels and the effects of environmental estrogens on reproductiv e success are poorly understood. To examine whether altered VTG expression predicts reproductive impairment, we exposed medaka (Oryzias latipes) for 2 or 8 weeks posthatch to 0, 0.5, 1.0, 2.5, and 7.5 ppb of the environmental estrogen o,p ' -DDT. Fish were sampled 2, 4, and 8 weeks after hatch to ex amine VTG expression and gonad development. After exposure, fish were trans ferred to clean water, grown to sexual maturity, and placed in mating pairs . We collected eggs for 7 days and scored them for fecundity (number of egg s), fertility (percent fertilized), and hatching success (percent hatched). DDT had no effect on VTG expression after a 2-week exposure, whereas all d oses induced VTG after 8 weeks. At both exposure durations, the highest dos es of DDT caused a female-skewed sex ratio in adults. Gonadal feminization appeared to be progressive: some ovotestes were observed after 2- or 4-week exposure to the two highest doses, but the proportion of ovaries increased after 8 weeks. Both 2- and 8-week exposures significantly reduced fertilit y and hatching success at all doses, with lower doses having a greater effe ct after longer exposure. Fertility and hatching success were more sensitiv e, to estrogenic disruption than were gonad differentiation and vitellogeni n expression. We suggest that VTG expression may be interpreted as a warnin g of reproductive consequences, but absence of expression cannot be interpr eted as absence of consequences.