Data from: The extent and meaning of hybridization and introgression between Siberian spruce (Picea obovata) and Norway spruce (P. abies): cryptic refugia as stepping stones to the west?

Boreal species were repeatedly exposed to ice ages and went through cycles of contraction and expansion while sister species alternated periods of contact and isolation. The resulting genetic structure is consequently complex, and demographic inferences are intrinsically challenging. The range of Norway spruce (Picea abies) and Siberian spruce (Picea obovata) covers most of northern Eurasia; yet their geographical limits and histories remain poorly understood. To delineate the hybrid zone between the two species and reconstruct their joint demographic history, we analysed variation at nuclear SSR and mitochondrial DNA in 102 and 88 populations, respectively. The dynamics of the hybrid zone was analysed with approximate Bayesian computation (ABC) followed by posterior predictive structure plot reconstruction and the presence of barriers across the range tested with estimated effective migration surfaces. To estimate the divergence time between the two species, nuclear sequences from two well-separated populations of each species were analysed with ABC. Two main barriers divide the range of the two species: one corresponds to the hybrid zone between them, and the other separates the southern and northern domains of Norway spruce. The hybrid zone is centred on the Urals, but the genetic impact of Siberian spruce extends further west. The joint distribution of mitochondrial and nuclear variation indicates an introgression of mitochondrial DNA from Norway spruce into Siberian spruce. Overall, our data reveal a demographic history where the two species interacted frequently and where migrants originating from the Urals and the West Siberian Plain recolonized northern Russia and Scandinavia using scattered refugial populations of Norway spruce as stepping stones towards the west.

寒带物种反复经历冰期，历经分布收缩与扩张的循环，而其姊妹物种则交替处于接触与隔离状态。由此形成的遗传结构极为复杂，种群历史推演本身极具挑战性。欧洲云杉（Picea abies）与西伯利亚云杉（Picea obovata）的分布范围覆盖了北欧亚大部分区域，但二者的地理界限与演化历史仍有待厘清。为刻画这两个物种间的杂交带并重构二者的联合种群历史，我们分别对102个种群的核简单序列重复（simple sequence repeat, SSR）标记变异与88个种群的线粒体DNA（mitochondrial DNA, mtDNA）变异展开分析。我们采用近似贝叶斯计算（approximate Bayesian computation, ABC）分析杂交带的动态特征，随后通过后验预测结构绘图重构杂交带模式，并借助估算的有效迁移表面检测研究范围内的基因流屏障分布。为估算两个物种的分化时间，我们针对每个物种的两个地理隔离种群的核序列展开近似贝叶斯计算分析。两大基因流屏障分隔了两个物种的分布范围：其一为二者间的杂交带，其二则将欧洲云杉的南部与北部分布区相隔离。该杂交带以乌拉尔山脉为核心区域，但西伯利亚云杉的遗传影响范围向西延伸更远。线粒体与核变异的联合分布模式显示，存在欧洲云杉的线粒体DNA向西伯利亚云杉的渐渗事件。综合来看，本研究的数据揭示了如下种群历史：两个物种间存在频繁的遗传交流；源自乌拉尔山脉与西西伯利亚平原的迁移种群，以零散分布的欧洲云杉冰期避难种群作为西迁踏脚石，重新拓殖了俄罗斯北部与斯堪的纳维亚半岛。