Morphological and molecular differentiation of invasive freshwater speciesof the genus Corbicula (Bivalvia, Corbiculidea) suggest the presence of three taxa in French rivers

Asiatic Clams are common in brackish and fresh water in Asia, and they were introduced into North America in 1924 and have now spread throughout the c ontinent. During the last two decades they have been reported in Europe, bu t the number of species here is uncertain. Populations of Corbicula from Fr ance and the Netherlands were analysed morphologically and genetically to q uantify the degree of species and/or population differentiation. The morpho logical and genetic data, based on allozymes and mitochondrial sequences, w ere in full agreement. They indicate that there are two distinct species, i dentified as C. fluminalis and C. fluminea, in the two countries. Analyses of the mitochondrial COI gene revealed an unexpected divergent population o f Corbicula in the Rhone. All these individuals were morphologically identi fied as C. fluminea, but had a COI sequence different from the two previous species. This population may, therefore, be a more ancient population, or a distinct species introduced via a different colonization route.