Assessing the impact of xenoestrogen exposure during larval development on the reproductive potential of the amphibian Silurana tropicalis in a partial life-cycle model

Abstract

Evidence suggests that chemicals acting as endocrine disruptors can modulate amphibian sex differentiation and induce sex reversal and gonadal abnormalities. However, consequences of gonadal abnormalities such as testicular oocytes on amphibian reproductive potential remain unclear. Assessing this linkage requires suitable experimental models, such as partial life-cycle exposure, in order to correlate accessible endpoints with apical endpoints indicative of reproductive fitness. Larvae of the emerging amphibian model Silurana tropicalis were exposed to EE2 in the ng/L range from NF stage 51-52 until completion of metamorphosis, and endpoints related to the reproductive function were assessed on completion of metamorphosis and at sexual maturity. Exposure to EE2 skewed the sex ratio toward phenotypic females in the treated groups, but also affected growth and development of the tadpoles. At sexual maturity, absence of one or both oviducts was observed in some female frogs that had been exposed to EE2. Regressed testicular oocytes were observed in most males, including males from the control group. The occurrence of regressed testicular oocytes seems to be dependent on genetic background, rather than xenoestrogens exposure. Mature testicular oocytes and presence of oviduct-like ducts in frogs displaying testis were only seen in treatment groups exposed to EE2. The incidence and the severity of gonadal abnormalities observed in Silurana tropicalis males and females exposed to EE2 were dependent on the nominal dose but also dependent on parentage. No link could be made between gonadal abnormalities and the reproductive potential of the frogs. These findings suggest that further development of partial life cycle models using Silurana tropicalis may be warranted in order to support identification and characterization of endocrine disrupters in chemical safety testing, for risk assessment and registration.