Data from: Spatial patterns of immunogenetic and neutral variation underscore the conservation value of small, isolated American badger populations

Small and isolated populations often exhibit low genetic diversity due to drift and inbreeding, but may simultaneously harbour adaptive variation. We investigate spatial distributions of immunogenetic variation in American badger subspecies (Taxidea taxus), as a proxy for evaluating their evolutionary potential across the northern extent of the species’ range. We compared genetic structure of 20 microsatellites and the Major histocompatibility complex (MHC) to evaluate if small isolated populations show low adaptive polymorphism relative to large and well-connected populations. Our results suggest that gene flow plays a prominent role in shaping MHC polymorphism across large spatial scales, while the interplay between gene flow and selection was stronger towards the northern peripheries. The similarity of MHC alleles within subspecies relative to their neutral genetic differentiation suggests that adaptive divergence among subspecies can be maintained despite ongoing gene flow along subspecies boundaries. Neutral genetic diversity were low in small relative to large populations, but MHC diversity within individuals was high in small populations. Despite reduced neutral genetic variation, small isolated populations harbour functional variation that likely contribute to the species evolutionary potential at the northern range. Our findings suggest that conservation approaches should focus on managing adaptive variation across the species range rather than protecting subspecies per se.

受遗传漂变与近交影响，小型孤立种群通常遗传多样性偏低，但同时可能携带有适应性变异。本研究以美洲獾（Taxidea taxus）亚种的免疫遗传变异空间分布作为替代指标，以此评估该物种分布北界范围内的演化潜力。我们对比了20个微卫星位点与主要组织相容性复合体（Major histocompatibility complex, MHC）的遗传结构，旨在探究相较于大型连通种群，小型孤立种群是否表现出更低的适应性多态性。研究结果表明，基因流在大空间尺度上对MHC多态性的塑造发挥着关键作用，而在物种分布的北部边缘区域，基因流与选择的交互作用更为强烈。相较于中性遗传分化，亚种内部的MHC等位基因相似性表明，尽管亚种边界沿线存在持续的基因流，亚种间的适应性分化仍可得以维持。小型种群的中性遗传多样性低于大型种群，但小型种群的个体内MHC多样性却更高。尽管中性遗传变异水平有所降低，小型孤立种群仍携带有功能性变异，这些变异或有助于该物种在北部分布区的演化潜力。本研究结果提示，保护策略应聚焦于在物种全分布范围内管理适应性变异，而非单纯保护亚种本身。