Whole genomes reveal subpopulations and isolation-by-distance patterns in the Norwegian lemming

<h4>Background</h4>The Norwegian lemming (Lemmus lemmus) is a small rodent endemic to the Fennoscandian alpine and arctic tundra. The species is known for cyclic population outbreaks and mass movements during peak years. Previous research based on microsatellites revealed high genetic variation but a weak population structure in the Norwegian lemming.<h4>Results</h4>In this study, we revisit the population structure of the species using genome-wide data. To do this, we generated a high-quality de novo reference genome for Lemmus lemmus, and resequenced genomes to 2.5-5 × coverage, from 86 lemmings sampled across the species' entire geographic distribution. Our results reveal that the population is geographically structured into distinct subpopulations, with an overall pattern characterised by isolation-by-distance among subpopulations. Furthermore, our results are consistent with earlier work suggesting that the species survived the last ice age within a northern refugium.<h4>Conclusions</h4>Together, these findings provide a genome-wide perspective on today's population structure of the Norwegian lemming. In addition, we provide a de novo reference genome, which we believe will be a valuable resource to the research community.