Evolutionary history of the land snail Helix aspersa in the Western Mediterranean: preliminary results inferred from mitochondrial DNA sequences

Intraspecific phylogeographic methods provide a means of examining the hist ory of genetic exchange among populations. As part of a study of the histor y of Helix aspersa in the Western Mediterranean, we performed a phylogeneti c analysis based on partial sequences of the mitochondrial large ribosomal subunit (16S) gene. Our samples include 31 H. a. aspersa populations from N orth Africa previously investigated for anatomical and biochemical characte rs. To clarify subspecific relationships, three individuals of the subspeci es H. a. maxima were also studied. The molecular phylogeny inferred agrees largely with previous results, in splitting H. a. aspersa haplotypes into a n eastern and a western group. H. a. maxima haplotypes form a third lineage arising before the H. a. aspersa groups. Divergence times estimated betwee n the lineages suggest that dispersal during Pleistocene glaciation and vic ariance events due to Pliocene geological changes in the western Mediterran ean may both have played a significant part in the establishment of the pre sent range of H aspersa.