Gene flow and mode of pollination in a dry-grassland species, Filipendula vulgaris (Rosaceae)

Filipendula vulgaris is a characteristic species of dry nonacidic grassland s in Denmark. This habitat type occurs only on marginal areas not suitable for agriculture or urbanization and that are by their nature fragmented. Th e population genetic structure of F. vulgaris was investigated in 17 popula tions within two regions of Denmark, using isozyme electrophoresis. Small p opulations were found to have significantly fewer polymorphic loci than lar ger populations, but all populations maintained the same common allelic var iants. The degree of isolation of individual populations did not affect the amount of genetic variation. Offspring arrays revealed a very high outcros sing rate (0.96). The field study demonstrated a very high level of gene fl ow between populations considering that small insects are thought to be the main pollinators of this species. An experiment to verify whether pollen t ransport by wind could explain the results from the field study demonstrate d long-distance transport from isolated plants to bagged plants. Filipendul a vulgaris pollen grains are very small and this explains why outcrossed pr ogeny were found using pollination bags with small pore sizes. We conclude that wind pollination is indeed possible and together with insect pollinati on is causing the observed patterns of genetic variation. The substantial g ene flow between populations may be reducing the effects of genetic drift i n the small fragmented populations of F. vulgaris.