Fragmentation of landscape as a cause for genetic subdivision in bank voles

We studied the barrier effects of various roadways on the genetic subdivisi on of bank vole (Clethrionomys glareolus) populations. Allele frequencies, genetic variability, and genetic distances of natural populations were calc ulated based on polymorphism of seven microsatellite markers. We compared b ank vole populations in control areas without such barriers with animals fr om both sides of a country road, a railway, and a highway. Using F and R st atistics, we demonstrated significant population subdivision in bank vole p opulations separated by the highway, but not in populations on either side of the other roadways or in the control area. Correlations between geograph ic and genetic distances were revealed by an extended method based on a Man tel analysis. This allowed us to measure genetic barrier effects and expres s them as additional geographic distances. For instance, statistically sign ificant differences in allele frequencies in all seven loci examined existe d among populations in southern Germany and Switzerland, which are separate d by the Rhine River and Lake Constance. The real geographic distance betwe en bank vole populations in Konstanz and those in Lengwil, Switzerland, was 6 km. According to this analysis the genetic barrier effect of the Rhine c ould be defined as an additional distance of 7.7 km. This study shows for t he first time that not only old geographic barriers but also more recent fr agmentation of landscape by, for example, highways has an important effect on gene flow and the genetic substructuring of populations, which should be considered in future environmental impact assessments.