RAPD analyses of hybridization events in Cardamine (Brassicaceae)

Recent hybrid speciation events between the diploid Cardamine rivularis and the diploid C. amara leading to the triploid C. xinsueta were investigated with random amplified polymorphic DNA (RAPD). The hybrid nature of C. xinsueta was confirmed by the additivity of RAPD markers which discriminate the parent species. An unexpectedly high level of genetic variation within C. xinsueta argues for several hybridization events and/or backcrossing with C. rivularis. A low number of nonparental bands in C. xinsueta indicates the younger age of this taxon. In contrast to the situation in C. xinsueta, low variability was observed in the hexaploid C. schulzii, a derivative species of C. xinsueta. C. schulzii probably originated recently by a single autopolyploidization event. The higher number of non-parental bands in C. schulzii is explained by the changing genetic variability of the parental populations. Evidence for potential gene flow across the ploidy levels is also provided.