Nuclear DNA restriction site polymorphisms and the phylogeny and population structure of an intertidal snail species complex (Littorina)

Primers for amplification of four novel, unlinked nuclear DNA loci, the first reported for the rough periwinkles of the genus Littorina, are described. Patterns of restriction site polymorphism for these loci are detailed within the rough periwinkles. RFLPs are not found to be diagnostic for any of the currently accepted species within this group, nor for any of the contentious subspecies, or forms, whose taxonomic status is uncertain. However, there are important differences in allele frequencies between these taxa and certain of these mirror differences detected in a previous study of the mitochondrial DNA. These allele frequency data are used to construct a phylogeny in which groupings of the three recognised species are obvious when either Nei's genetic distances or Reynold's distances are clustered. Contentious forms (L. neglecta, L. saxatilis 'b' and L. tenebrosa) do not cluster as distinct taxa, although populations of L. neglecta have important allele frequency differences from L. saxatilis. These four loci have confirmed the consensus view of Littorina phylogeny and provided important information on population structure-however four loci is insufficient for reaching definitive conclusions. Since analysis of nuclear DNA polymorphisms such as these is invaluable for analysis of phylogeny, population structure and phylogeography, identification of additional loci is considered imperative.