Molecular variation in Leymus species and populations

Icelandic populations of European lymegrass [Leymus arenarius (L.) Hochst.] were examined using amplified fragment length polymorphism (AFLP) and rest riction fragment length polymorphism (RFLP) of the major ribosomal genes (1 8S-5.8S-26S rDNA), in comparison with Alaskan populations of its closely re lated species L. mollis (Trin.) Pilger. The AFLP profiles emerged as two di stinct entities, clearly separating the two species, and based on species-s pecific bands it was simple to distinguish these two morphologically simila r species. The rDNA-RFLPs also differentiated the species. Within species, the Icelandic L. arenarius was more homogeneous than the Alaskan L. mollis, and its variation was dispersed over geographically different populations, suggesting a common gene pool. The variation among the Alaskan L. mollis w as more extensive and its interrupted pattern may be the result of gene int rogression at subspecies level. Within a 40-year-old population of L. molli s established in Iceland from Alaskan material, the molecular profiles sepa rated old and new genotypes. Both AFLP and rDNA revealed the new genotypes to be extremely similar. This rapid change in allele frequency is thought t o be the result of adaptation to a new environment.