Understanding the population genetic structure of coastal species (Cakile maritima):: seed dispersal and the role of sea currents in determining population structure

The nature and extent of long-distance seed dispersal are currently poorly understood, largely due to the inherent difficulty in detecting such a phenomenon. Genetic methods provide one of the few general approaches that offer the potential to accurately address this issue. Phenotypic and allozymic approaches were applied to characterize inter-population seed dispersal of the sea rocket (Cakile maritima, Brassicaceae), a glabrous and succulent annual herb. Genetic variation was assessed on 360 individuals sampled from nine populations. Genetic diversity across populations was high, 37 % of which was represented by Qst and 16 % by Fst. When genetic distances were used to construct the UPGMA dendrogram, populations were clustered into three groups at the 90 % similarity level. The pattern of clustering can be explained by examining the direction of sea currents around Tunisian coasts. We have shown in this study that C. maritima seeds can survive up to 4 months immersion in sea water and up to I year of floating in sea water; therefore, seed dispersal between populations is possible both in terms of seed survival and current patterns.