EVIDENCE FOR SPATIAL STRUCTURE AND DIRECTIONAL GENE FLOW IN A POPULATION OF AN AQUATIC PLANT, POTAMOGETON COLORATUS

Six hundred and forty-seven samples of Potamogeton coloratus from 60 d itches in the Gordano Valley, Somerset were analysed for variation at two polymorphic PGM isozyme loci using starch gel electrophoresis. A t otal of eight genotypes was detected, and a high level of partitioning of genetic variability between ditches was observed with F-ST=0.575. Genetic variability was shown to increase with distance from the head of the valley. The genetic subdivision of the population and pattern o f increasing diversity downstream and downwind were attributed to gene tic bottlenecks, associated with ditch cleaning events, and subsequent directional gene flow mediated by the prevailing wind and water curre nts.