Data from: Lack of spatial immunogenetic structure among wolverine (Gulo gulo) populations suggestive of broad scale balancing selection

Elucidating the adaptive genetic potential of wildlife populations to environmental selective pressures is fundamental for species conservation. Genes of the major histocompatibility complex (MHC) are highly polymorphic, and play a key role in the adaptive immune response against pathogens. MHC polymorphism has been linked to balancing selection or heterogeneous selection promoting local adaptation. However, spatial patterns of MHC polymorphism are also influenced by gene flow and drift. Wolverines are highly vagile, inhabiting varied ecoregions that include boreal forest, taiga, tundra, and high alpine ecosystems. Here, we investigated the immunogenetic variation of wolverines in Canada as a surrogate for identifying local adaptation by contrasting the genetic structure at MHC relative to the structure at 11 neutral microsatellites to account for gene flow and drift. Evidence of historical positive selection was detected at MHC using maximum likelihood codon-based methods. Bayesian and multivariate cluster analyses revealed weaker population genetic differentiation at MHC relative to the increasing microsatellite genetic structure towards the eastern wolverine distribution. Mantel correlations of MHC against geographical distances showed no pattern of isolation by distance (IBD: r = -0.03, p = 0.9), whereas for microsatellites we found a relatively strong and significant IBD (r = 0.54, p = 0.01). Moreover, we found a significant correlation between microsatellite allelic richness and the mean number of MHC alleles, but we did not observe low MHC diversity in small populations. Overall these results suggest that MHC polymorphism has been influenced primarily by balancing selection and to a lesser extent by neutral processes such as genetic drift, with no clear evidence for local adaptation. This study contributes to our understanding of how vulnerable populations of wolverines may respond to selective pressures across their range.阐明野生动物种群应对环境选择压力的适应性遗传潜力，对于物种保护而言至关重要。主要组织相容性复合体（major histocompatibility complex, MHC）基因具有高度多态性，在宿主针对病原体的适应性免疫应答中发挥关键作用。MHC多态性与促进本地适应的平衡选择或异质选择密切相关。然而，MHC多态性的空间分布格局同时受到基因流与遗传漂变的影响。狼獾具有极强的扩散能力，栖息于包括北方针叶林、泰加林、苔原以及高海拔高山生态系统在内的多样生态区域。本研究以加拿大境内的狼獾种群为研究材料，通过对比MHC与11个中性微卫星标记的遗传结构以控制基因流与遗传漂变的影响，将其作为识别本地适应的替代策略，对狼獾的免疫遗传变异展开探究。本研究基于密码子的最大似然法，在MHC基因中检测到历史正向选择的信号。贝叶斯聚类与多变量聚类分析结果显示，相较于随狼獾分布区东扩而逐渐增强的微卫星遗传结构，MHC位点的种群遗传分化程度更低。MHC与地理距离的曼特尔相关性分析未显示出距离隔离（Isolation by Distance, IBD）模式（r=-0.03，p=0.9）；而微卫星标记则呈现出较强且显著的距离隔离信号（r=0.54，p=0.01）。此外，本研究发现微卫星等位基因丰富度与MHC等位基因平均数量之间存在显著相关性，但并未在小型种群中观察到MHC多样性降低的现象。综合来看，上述结果表明MHC多态性主要受到平衡选择的影响，仅在较小程度上受到遗传漂变等中性进化过程的作用，未发现本地适应的明确证据。本研究有助于加深我们对狼獾脆弱种群如何应对其分布范围内各类选择压力的认知。