Species relationships and population structure of Littorina saxatilis Olivi and L. tenebrosa Montagu in Ireland using single-strand conformational polymorphisms (SSCPs) of cytochrome b fragments

Littorina saxatilis is a ubiquitous snail of intertidal habitats in the Nor th Atlantic. Shell type in littorinids is extremely polymorphic and defined by habitat. Taxonomy based upon shell type has been revised in the light o f anatomic and genetic information, but uncertainties remain. In this study , the population structure of L. saxatilis and L. tenebrosa was studied at 11 sites in Ireland using single-strand conformational polymorphisms of a 3 75-bp portion of the cytochrome b gene, and the status of L. tenebrosa, the small, fragile-shelled, brackish water type, was considered. The genetic p atterns among L. saxatilis and L. tenebrosa populations were examined over varying distances and L. tenebrosa was compared with adjacent L. saxatilis populations at four sites on the west coast of Ireland and one site on the east coast. Haplotype diversity was high with 32 haplotypes present among 9 95 individuals. Pairwise tests suggest gene flow over small scales among an d between habitat types and may reflect the stochastic legacy of postglacia l recolonization over larger scales. In AMOVA tests, geography explained ne arly twice as much of the variance (30%) as habitat type (18%), indicating that gene now is more restricted by distance than by habitat type, and supp orting the status of L. tenebrosa as an ecotype of L. saxatilis rather than a separate species.