DECLINING GENETIC DIVERSITY AND INCREASING GENETIC ISOLATION TOWARD THE RANGE PERIPHERY OF STIPA PENNATA, A EURASIAN FEATHER GRASS

A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species' geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata, by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic bands = 21.2%) and moderately high genetic differentiation among them (mean Phi(ST) = 0.29). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic differentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral populations may experience higher genetic drift and lower gene flow than their central counterparts, possibly because of smaller population sizes, spatial isolation, and a more complex landscape structure. In addition, historic range fluctuations and the mixed breeding system could have enhanced the observed patterns in our study species.