Genetic variation in the clonal bryophyte Hylocomium splendens at hierarchical geographic scales in Scandinavia.

The widespread bryophyte Hylocomium splendens was sampled in a hierarchical fashion from populations representing four Scandinavian vegetation zones. Allozyme electrophoresis revealed variation at 11 out of 13 screened loci, allowing accurate identification of genotypes. From a total sample of 298 shoots 79 genotypes could be detected, giving the proportion of distinguishable genotypes (PD) of 0.265. The total allelic diversity (HT) based on polymorphic loci was 0.274. The relative differentiation among populations was low (GST=0.073), indicating a high level of gene flow. Differences in population structuring occurred between a subarctic-alpine site vs. three lowland sites. The subarctic-alpine population had one widespread clone, which appeared to be propagated by dispersal of vegetative fragments. That population also comprised many rare genotypes, often occurring together within 10´10 cm patches. The lowland populations had genotypes that were locally common and often dominant within the patches. When identical genotypes were observed in multiple patches within these populations, it was usually statistically highly probable that they had arisen by independent sexual recombinations.