Genetic structure of Saxifraga tridactylites (Saxifragaceae) from natural and man-made habitats.

In contrast to many declining plant species Saxifraga tridactylites extended its distribution range in the man- made landscape of central Europe. The species naturally colonizes rocks and calcareous grasslands, but has also spread enormously in anthropogenic habitats such as railway constructions during the last decades. To analyze the genetic structure of the species 216 individuals from 8 populations in natural and 5 populations in man-made habitats were studied using AFLPs. The molecular analysis resulted in 250 scorable fragments. Population variability, measured as Nei's gene diversity, Shannon's Information Index and percentage of polymorphic bands, was slightly but not significantly higher in populations from natural habitats and was not correlated with population size. Mantel test indicated no significant correlation between pairwise genetic (ɸPT) and geographic distances. An analysis of molecular variance revealed significant differentiation between the two habitat types. About 9% variability were observed between natural and man-made habitats, 21% among populations within these two habitats and 70% within populations. In a neighbour joining cluster analysis populations from natural and man-made habitats were clearly separated from each other. Populations of S. tridactylites from man-made habitats do, therefore, not suffer from reduced genetic diversity. The observed genetic differentiation between populations from man-made and natural habitats could be due to reduced gene flow and/or habitat specific selection. However, the results of the study clearly demonstrate human impact on the genetic structure of plant populations in man-made landscapes. [ABSTRACT FROM AUTHOR]