Genetic structure of Euphrasia stricta on the Baltic island of Gotland, Sweden

摘要

Genetic differentiation between and within five varieties of Euphrasia stricta (var. brevipila, var. gotlandica, var. stricta, var. suecica and var. tenuis) on Gotland was investigated, using amplified fragment length polymorphism, AFLP. The varieties are described in the literature by morphology and association to habitat type. We wanted to investigate whether the varieties are locally adapted populations to the typical habitat type for each variety or if they are preadapted to certain habitat types and have colonized Gotland in their present form.A constrained principal coordinate analysis revealed three genetically differentiated subunits within the species. The two early-flowering varieties suecica and tenuis each formed a distinct group, while the three late-flowering varieties brevipila, gotlandica and stricta together formed the third group. A phylogenetic tree confirms the partitioning into three groups. Within the group containing the late-flowering varieties there are populations that pair as each other's closest relatives, but belong to different varieties. These pairs are also geographically adjacent.The phylogenetic tree had a "star-like" appearance indicating a stronger divergence between populations than between varieties. The same pattern was seen in the partitioning of genetic diversity, with a lower amount of genetic variation occurring between varieties, F-ST=0.14, than between populations within the varieties, F-ST ranging from 0.26 to 0.60.In Euphrasia stricta the varieties suecica and tenuis and the group containing the varieties stricta/gotlandica/brevipila are likely to have a phylogeographical history outside Gotland, or an ancient and concealed local origin on the island. Within the group stricta/gotlandica/brevipila local evolutionary events seem to determine the variety identity, probably through local adaptation.