Is aphallic vas deferens development in females related to the distance from organotin sources? A study with Stramonita haemastoma.

Imposex, a syndrome characterized by the appearance of a penis and/or vas deferens in female gastropods due the presence of organotins in environment, is still observed in Brazilian gastropod populations, as in other countries, even after the tributyltin (TBT) ban. Nevertheless, the progressive controls on the use of organotins in antifouling systems at national and international levels and the consequent reduction of their environmental concentrations have led to changes in the characteristics of imposex development observed in Stramonita haemastoma. Populations of this species were analyzed on the coast of Rio de Janeiro (Brazil) between 2007 and 2008, and the developmental pathways associated with the syndrome were identified. Compared with previous works, it was noted that imposex expression was reduced in most of Guanabara Bay. Aphallic imposex development, on the other hand, showed a marked increase. The pathways of imposex development were also evaluated in a temporal data series from a fixed sampling station at Vermelha beach, and the incidence of aphallic imposex development was found to show a marked increase from 1998 onward. Furthermore, the observation of either the presence or absence of a penis in imposex-affected females may indicate that penis development is related to the contaminant exposure level and that the decreasing TBT concentrations in the local environment result in the predominance of an aphallic route of imposex development. These findings support the idea that imposex female aphally in this species could be a dose-dependent response, rather than a genetic anomaly.