Anatomical And Histological Studies On Imposex Of Marine Gastropods

Anatomical and histological studies on imposex of marine gastropodsOrganotin compounds, especially tributyltin (TBT), are widely used as biocidal additives in antifouling paints because of their effectiveness. However, they also cause severe damages to non-target organisms while they kill fouling organisms. For example, TBT has been reported to induce imposex in gonochoristic gastropods, that is, imposition of male sexual organs such as penis and vas deferens on female sexual organs.The present thesis evaluated 10 species of marine gastropods of families Muricidae, Buccinidae, Conidae and Cypreaidae that are widely distributed along the Southeast Coast Waters of China, and found that all of them are imposex species. The specific objectives are to describe anatomical and histological structure of male, female and imposex genital system, and to investigate annual reproduction cycle and developmental process of egg capsules in Thais clavigera, which is considered as an ideal species for biomonitoring organotin contamination along Southeast China Sea.Interspecific similarities and differences were found in the development of the genital systems of males and females and the male sex organs of imposexes. In general, morphological and histological structures of penis and vas deferens of imposexes were similar to those of normal males, but differences were also observed in a few imposexed females. Despite their similarities in the development and structure between the imposexed female and normal male, the imposex individuals may have the potential to perform the function of male sex organs, but could not function as males. In the present study, sterile imposexed females caused by the rupture of capsule gland were found in 4 species of 3 families, and sterile imposexed females without the rupture of capsule gland were found in 2 species of 2 families. In addition, the development of ovary in 2 species was restrained due to imposex.Anatomical observations were found in good agreement with histological studies on the periodic development of reproductive gonad, suggesting anatomical observation would be an effective, sufficient and simpler tool to evaluate the gonad maturity of T. clavigera. Although percentage of imposex as high as 100% in T. clavigera was found in Beishan Bay of Shantou, its sex ratio remained as normal. Because the length of penis of male T.clavigera varied with its gonad maturity, the variation of penis length along with the gonad cycle should be taken into account when the RPSI and RPLI are used as bio-indicators for organotin contamination.The reproductive failure in imposexed females may pose severe threat on the population succession of marine gastropods, however, there is no evidence existed indicating that territorial population extinction have occurred for the 10 species investigated in the present study. Instead of using T. clavigera alone, a combination of imposexed T. clavigera, Babylonia sp. and Chicoreus sp. was suggested to form a complete bio-monitoring system for organotin pollution along the Southeastern China Sea. Endocrine disrupting chemicals (EDCs) such as organotin compounds may threaten human health through the amplification of food chains, the present paper intends to provoke our government to support and fund more extensive investigations and research on the ecological effects of EDCs.