OVIDUCT MALFORMATION AS A STERILIZING EFFECT OF TRIBUTYLTIN (TBT)-INDUCED IMPOSEX IN OCENEBRA-ERINACEA (GASTROPODA, MURICIDAE)

In populations subject to high tributyltin (TBT) pollution, females of the neogastropod Ocenebra erinacea exhibit a characteristic malformat ion of the oviduct as an effect of advanced imposex. This abnormality is a longitudinal split of the oviduct wall, causing the bursa copulat rix and capsule gland to open directly into the pallial (mantle) cavit y. When first discovered it was assumed such a gross malformation woul d preclude sperm transfer and capsule formation. Field evidence in ter ms of a general paucity of juveniles in affected populations supported this idea but direct evidence of a sterilising effect was lacking. La boratory spawning experiments using normal and affected females have n ow been carried out. No capsule was produced by any female having a sp lit oviduct. Thus, it is concluded that the net effect of the conditio n is sterilisation. The larvae of O. erinacea escape from capsules as veligers that assume a planktonic existence lasting for up to 5 days. The duration of this swimming phase is sufficient to permit extensive dispersion and subsequent colonisation over a wide area, including con taminated localities. Populations close to TBT sources could therefore be sustained by a supply of recruits from less-contaminated areas and their nonbreeding status thus masked. Juvenile females reared to one- year-old in water with a mean TBT concentration of 3 ng Sn 1(-1) exhib ited the split oviduct condition seen in adults at contaminated sites, whereas those reared similarly at TBT levels of 0.2-0.3 ng Sn 1(-1) a ppeared normal. The disruption of the early ontogeny of the female rep roductive tract, which leads to adult sterility, can be interpreted as an subtle effect of masculinization induced by TBT exposure.