Imposex and novel mechanisms of reproductive failure induced by tributyltin (TBT) in the freshwater snail Pomacea canaliculata

Abstract

The effects of TBT on mortality and reproduction were studied in this invasive snail. The nominal fifty percent lethal concentration (LC50) was 9 Dg TBT/L, after 28 days. The nominal no observed effect on lethality concentration? (NOECL) was 6 Dg TBT/L after the same period. Male-female couples and females that had been group-mated but were isolated from males during the experiment (isolated females) were exposed (28 d) to either 0 or 6 Dg/L of TBT (nominal NOECL-exposed). Copulation and oviposition frequencies, egg clutch mass and percent egg fertility were recorded. Gonads (both sexes) and the seminal receptacle (females) were studied histologically at the end of the experiment. A significant decrease in copulation frequency was observed in mated-exposed females. Exposure also decreased oviposition frequency of mated exposed and isolated-exposed females, but only the latter reached significance. No differences in either egg clutch mass or percent fertility were observed at first oviposition but both parameters were drastically reduced in subsequent egg clutches of exposed females. No histological alterations were observed in gonads of TBT-exposed animals; however, sperm storage in the seminal receptacle was drastically decreased in exposed females. Imposex but no oviductal obstruction was observed in all exposed females. It is concluded that TBT induces reproductive failure in P. canaliculata by decreasing copulation frequency and by severely affecting sperm storage by the female.