Data from: Influence of northern limit range on genetic diversity and structure in a widespread North American tree, sugar maple (Acer saccharum Marshall)

Due to climate change, the ranges of many North-American tree species are expected to shift northward. Sugar maple (Acer saccharum Marshall) reaches its northern continuous distributional limit in north-eastern North America at the transition between boreal mixed-wood and temperate deciduous forests. We hypothesized that marginal fragmented northern populations from the boreal mixed-wood would have a distinct pattern of genetic structure and diversity. We analyzed 18 microsatellite loci variation in 23 populations distributed along three latitudinal transects (west, central and east) that encompass the continuous-discontinuous species range. Each transect was divided into two zones, continuous (temperate deciduous) and discontinuous (boreal mixed-wood), based on sugar maple stand abundance. Respective positive and negative relationships were found between the distance of each population to the northern limit (D north), and allelic richness (AR) and population differentiation (FST). These relations were tested for each transect separately; the pattern (discontinuous/continuous) remained significant only for the western transect. structure analysis revealed the presence of four clusters. The most northern populations of each transect were assigned to a distinct group. Asymmetrical gene flow occurred from the southern into the four northernmost populations. Southern populations in Québec may have originated from two different postglacial migration routes. No evidence was found to validate the hypothesis that northern populations were remnants of a larger population that had migrated further north of the species range after the retreat of the ice sheet. The northernmost sugar maple populations possibly originated from long distance dispersal.受气候变化影响，众多北美树种的分布范围预计将向北迁移。糖枫（Acer saccharum Marshall）在北美东北部的北方混交林与温带落叶林的过渡地带，达到其连续分布范围的北界。本研究假设：源自北方混交林的边缘碎片化北部种群，其遗传结构与遗传多样性模式将具有独特性。本研究对覆盖该物种连续-间断分布范围的3条纬度样带（西、中、东）上的23个种群的18个微卫星位点（microsatellite loci）变异进行了分析。依据糖枫林分的丰度，每条样带被划分为两个区域：连续分布区（温带落叶林）与间断分布区（北方混交林）。研究发现，种群距北界的距离（D north）分别与等位基因丰富度（allelic richness, AR）和种群分化（FST）呈正相关与负相关关系。对上述相关关系分别在每条样带中进行检验，结果显示仅西部样带的间断/连续分布区差异模式仍具有统计学显著性。群体结构分析显示存在4个遗传聚类群，每条样带最北端的种群均被归入一个独立的聚类群。存在不对称的基因流：基因从南部种群流向4个最北部种群。魁北克省的南部种群可能源自两条不同的冰后迁移路径。本研究未发现证据支持以下假说：北部种群是冰盖消退后，曾迁移至该物种分布范围以北的更大种群的遗留群体。最北部的糖枫种群可能源自长距离扩散事件。