Imposex
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Imposex is a descriptive term applied to some sea snails, marine gastropod mollusks which, under the toxic effects of pollutants, develop sex organs that are in contrast to their actual sex. It is a pathological condition where male sex characteristics, such as the development of male sex organs, (for example the penis and the vas deferens) form in female gastropods.
The only confirmed inducer of imposex is tributyltin,[1] which can be active in extremely low concentrations. Tributyltin is an anti-fouling agent for boats which affects females of the species Nucella lapillus (dog whelk) and more than 200 other marine gastropods. The penis growth of imposex female dog whelks blocks the oviduct, although ovule production continues. An imposex female dog whelk passes through several stages of penis growth, before it is unable to contain its constant production of ovules. Later stages of imposex can lead to the sterility and premature death of the females, affecting the entire population.
The imposex stages of female dog whelks (Nucella lapillus) and other molluscs (including Nucella lima) are used in the United Kingdom and worldwide to monitor levels of tributyltin. The RPSI (Relative Penis Size Index) of females to males, and the VDSI (Vas Deferens Sequence Index) are used to monitor levels of tributyltin in marine environments.
On September 29, 2007, the Halifax, Nova Scotia-based newspaper The Chronicle Herald featured a story on female dogwhelks on the shores of Halifax Harbour and other parts of Nova Scotia, where they live on the beach in intertidal zones. The report stated that female dogwhelks still grow penises even after a ban on tributyltin.[2]
[edit] References
- ^ Ruiz JM, Quintela M, Barreiro R (1998) Tributyltin and imposex. no uncertainty shown. Mar Ecol Prog Ser 170: 293-294
- ^ "Tiny Snail, Big Problem" The Chronicle Herald, Halifax, NS, Canada. Sat, September 29th, 2007. http://www.thechronicleherald.ca/Science/914854.html
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- Gibbs, P.E., Bryan, G.W. (1986). Reproductive failure in populations of the dog-whelk Nucella lapillus, caused by imposex induced by tributyltin from antifouling paints. J. Mar. Biol. Ass. U.K. 66: 767-777.
- "Occurrence of Imposex." Natural Resource Management. 2006.
- Wirzinger, G., Vogt, C., Bachmann, J., Hasenbank, M., Liers, C., Stark, C., Ziebard, S. & Oehlmann, J. (2007). Imposex of the netted whelk Nassarius reticulatus (Prosobranchia) in Brittany along a transect from a point source. Cah. Biol. Mar. 48(1): 85-94.
