Genetic differentiation of common shrew Sorex araneus populations among different alpine valleys revealed by microsatellites

Geographical barriers may affect the genetic structure of populations by re ducing gene exchanges among them. In Switzerland, the common shrew Sorer ar aneus Linnaeus, 1758 is mostly confined to mountainous areas because of a c ompeting sister species, Millet's shrew S. coronatus Millet, 1828, which oc cupies most of the Swiss lowlands. The structure of common shrew population s found in different alpine valleys may therefore be affected by the topogr aphy. Using microsatellites, genetic structuring of seven shrew populations is investigated among four different valleys of, the Swiss Alps. Using the exact G-test, significant genetic structuring is detected between several valleys. Isolation by distance does not fully explain our results. It appea rs that high mountain ridges (> 2400 m) can significantly reduce gene flow. F- and R-statistics are estimated and compared to the exact G-tests result s. Mantel tests show that F-ST, unlike R-ST, is significantly correlated wi th differentiation. F-ST remains however low even at high differentiation l evels, while R-ST has a high variance. We discuss how these results may hav e wider implications with regards the interpretation of microsatellite data . Finally, a new microsatellite locus, L99, appears to discriminate S. aran eus of the Vaud and Cordon races from both S. araneus Valais and S. coronat us.