Data from: 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 equivalent distances, the southern sub-regions were genetically more similar to each other than those in the north, which indicates that the prolonged periods of interrupted lemming cyclicity recorded in the northern parts of Fennoscandia have led to increased isolation and population differentiation. In summary, we propose that mass movements during peak years act as pulses of gene flow between mountain tundra areas, and that these help to maintain genetic variation and counteract differentiation over vast geographic distances.

挪威特有旅鼠（Lemmus lemmus）是种群周期性波动物种的标志性代表，自中世纪起便因其大规模种群暴发与集体迁徙行为闻名于世。尽管学界已针对该周期性波动的驱动机制开展了大量深入研究，但对于种群高峰期间的长距离扩散究竟能在多大程度上促成山地苔原区域间的基因流，目前仍几乎一无所知。本研究采用9个微卫星标记（microsatellite markers）解决这一科学问题，对芬诺斯坎迪亚各亚区的全域遗传多样性及种群分化水平进行了分析。研究结果显示，该物种具有较高的遗传变异水平，种群结构分化程度却异常微弱，这与体型更大的哺乳动物的种群遗传结构特征相似。种群分化整体呈现为沿物种全分布范围的遗传渐变群，空间自相关分析结果表明，基因流发生的频率足够高，可形成100公里的遗传斑块尺度。此外，研究发现，在地理距离相当的前提下，芬诺斯坎迪亚南部亚区的种群遗传相似性高于北部亚区，这表明芬诺斯坎迪亚北部地区记录到的旅鼠周期性波动长期中断的现象，已导致种群隔离程度加剧与种群分化水平提升。综上，本研究提出，种群暴发年份的集体迁徙行为可作为山地苔原区域间的基因流脉冲，助力维持大范围地理尺度下的遗传多样性，并抵消种群分化进程。