Molecular phylogenetic relationships in the aquatic snail genus Lymnaea, the intermediate host of the causative agent of fascioliasis: insights from broader taxon sampling.

Phylogenetic analyses were performed on partial mitochondrial (16S) gene sequences that included new 16S data for 23 exemplars of the freshwater pulmonate snail genus Lymnaea sensu lato and putative outgroup species. This procedure yielded relatively congruent patterns of evolutionary divergence and phylogenetic affinities, and greater resolution and support for many lineages at different levels of divergence than from a previous work based on fewer samples. It has also clarified the relationships between key taxa. Molecular differentiation was evident among genera. Lymnaeids with n=16 chromosomes are a distinct, well-supported monophyletic group of recent origin. The genus Radix appears to be paraphyletic. Among the indigenous North American lymnaeids, a closer alliance was found between Fossaria spp. and Stagnicola caperata, a member of the subgenus Hinkleyia, than between the latter species and members of the subgenus Stagnicola s.str. The North American population of Lymnaea stagnalis is likely to be of European origin as it clustered with its European counterparts. The relevance of the molecular findings to efforts aimed at controlling snail-transmitted trematode diseases is discussed.