Run to the hills: gene flow among mountain areas leads to low genetic differentiation in the Norwegian lemming

The endemic Norwegian lemming (Lemmus lemmus) is an icon for cyclic species, famous since the Middle Ages for its enormous population outbreaks and mass movements. Although the drivers behind this cyclicity have been intensively investigated, virtually nothing is known about the extent to which long-distance dispersal during population peaks actually lead to gene flow among mountain tundra areas. In this article, we use nine microsatellite markers to address this question and analyse range-wide genetic diversity and differentiation between Fennoscandian sub-regions. The results revealed a high genetic variation with a surprisingly weak population structure, comparable to that of much larger mammals. The differentiation was mainly characterized as a genetic cline across the species' entire distribution, and results from spatial autocorrelation analyses suggested that gene flow occurs with sufficiently high frequency to create a genetic patch size of 100 km. Further, we found that for the...