Genetic Structure, Gene Flow and Reproductive Ecology in Sand-Dune Populations of Polygala Vulgaris

(1) Large populations of Polygala vulgaris occur in Oxwich and Whiteford sand-dune systems on the Gower Peninsula, South Wales. These populations are polymorphic for flower colour and in four enzyme systems detected by electrophoresis. (2) At Oxwich, several flower colour and enzyme morphs occur, but large patches, containing hundreds or thousands of plants, were monomorphic in all systems. These groups adjoin in a few places and there is evidence of recent small changes in the distribution of the morphs with a very limited amount of hybridization between them. (3) At Whiteford there is less variation in both flower colour and the enzyme systems and the plants occur in small, mainly monomorphic, patches in a mosaic pattern over the dune system. (4) Insects, mainly bumblebees, visited P. vulgaris for nectar in small numbers but many flowers must remain unvisited, and fluorescent dust applied to the anthers of thirteen inflorescences was only dispersed from two. The species is self-compatible and largely selfpollinating. (5) Seeds of P. vulgaris have an elaiosome attached to one end and were taken readily by the ant, Lasius niger, which carried the seeds into their nests, often ejecting them again after mutilating the elaiosome. The ants carried the seeds up to 2 m. No other adaptations for seed dispersal are apparent, but occasional long distance dispersal, e.g. by wind or on the feet of grazing animals, may have an important effect on the genetic structure of the populations. (6) Neighbourhood area and size are small and allow the possibility of local differentiation within each population. (7) The large monomorphic groups seem to have established at Oxwich as a result of substantial recolonization from disturbance after 1945. At Whiteford many small recolonizations must follow frequent covering with blown sand leading to a mosaic of small monomorphic patches. In both populations, genetic drift appears to have had a large effect in determining the present-day genetic structure.