High gene flow in the American badger overrides habitat preferences and limits broadscale genetic structure

Habitat associations are a function of habitat preferences and dispersal capabilities, both of which can influence how species responded to Quaternary climatic changes and contemporary habitat heterogeneity. Predicting resultant genetic structure is not always straightforward, especially in species where high dispersal potential and habitat preferences yield opposing predictions. The American badger has high dispersal capabilities that predict widespread panmixia, but avoids closed-canopy forests and clay soils, which could restrict gene flow and create ecologically based population genetic structure. We used mitochondrial sequence and microsatellite data sets to characterize how these opposing forces contribute to genetic structure in badgers at a continent-wide scale. Our data revealed an overall lack of ecologically based population genetic structure, suggesting that high dispersal capabilities were sufficiently realized to overcome most habitat-based genetic structure. At a broadscale, badger gene flow is limited only by geographic distance (isolation by distance) and large water barriers (Lake Michigan and the Mississippi River). The absence of genetic structure in a species with strong avoidance of unsuitable habitats advances our understanding of when and how genetic structure emerges in widespread, highly mobile species.

栖息地关联是栖息地偏好与扩散能力共同作用的结果，二者均可影响物种对第四纪气候变化以及当代生境异质性的响应模式。预测由此产生的种群遗传结构往往并非易事，尤其当高扩散潜力与栖息地偏好得出相互对立的预测结果时，这一难题更为突出。美洲獾（American badger）具备极强的扩散能力，理论上应形成广泛的泛交（panmixia）种群，但该物种会避开郁闭林与黏质土壤，这类生境或可限制种群间的基因交流，进而催生基于生态差异的种群遗传结构。本研究借助线粒体序列（mitochondrial sequence）与微卫星数据集（microsatellite data sets），在大陆尺度上解析了这两种对立演化压力如何共同塑造美洲獾的种群遗传结构。研究结果显示，整体上未观测到基于生态差异的种群遗传结构，表明美洲獾的高扩散能力足以抵消绝大多数由生境差异引发的遗传分化。在大空间尺度下，美洲獾的基因交流仅受地理距离（距离隔离，isolation by distance）与大型水域屏障（密歇根湖（Lake Michigan）、密西西比河（Mississippi River））的限制。对于这类具备强烈不适生境规避偏好却未显现明显遗传结构的物种而言，本研究结果深化了我们对广布性、高移动性物种的种群遗传结构形成时机与作用机制的认知。