Data from: Multilocus analysis of nucleotide variation and speciation in three closely related Populus (Salicaceae) species

Historical tectonism and climate oscillations can isolate and contract the geographical distributions of many plant species, and they are even known to trigger species divergence and ultimately speciation. Here, we estimated the nucleotide variation and speciation in three closely related Populus species, Populus tremuloides, P. tremula and P. davidiana, distributed in North America and Eurasia. We analysed the sequence variation in six single-copy nuclear loci and three chloroplast (cpDNA) fragments in 497 individuals sampled from 33 populations of these three species across their geographic distributions. These three Populus species harboured relatively high levels of nucleotide diversity and showed high levels of nucleotide differentiation. Phylogenetic analysis revealed that P. tremuloides diverged earlier than the other two species. The cpDNA haplotype network result clearly illustrated the dispersal route from North America to eastern Asia and then into Europe. Molecular dating results confirmed that the divergence of these three species coincided with the sundering of the Bering land bridge in the late Miocene and a rapid uplift of the Qinghai-Tibetan Plateau around the Miocene/Pliocene boundary. Vicariance-driven successful allopatric speciation resulting from historical tectonism and climate oscillations most likely played roles in the formation of the disjunct distributions and divergence of these three Populus species.

历史构造运动与气候震荡可隔离并收缩诸多植物物种的地理分布范围，甚至已知其会引发物种分化并最终导致物种形成。本研究针对分布于北美与欧亚大陆的3个近缘杨属（Populus）物种——美洲颤杨（Populus tremuloides）、欧洲山杨（P. tremula）以及山杨（P. davidiana）——开展研究，估算其核苷酸变异与物种形成过程。我们对采自这3个物种全分布区内33个种群的497份个体样本，开展了6个单拷贝核基因座与3个叶绿体（cpDNA）片段的序列变异分析。这3个杨属物种均呈现出相对较高的核苷酸多样性水平，且核苷酸分化程度显著。系统发育分析结果显示，美洲颤杨的分化时间早于另外两个物种。叶绿体单倍型网络分析结果清晰揭示了其从北美向东亚、再向欧洲的扩散路径。分子定年结果证实，这3个物种的分化时间与中新世晚期白令陆桥的断裂，以及中新世/上新世交界时期青藏高原的快速隆升时间相吻合。由历史构造运动与气候震荡引发的、受地理分替驱动的成功异地物种形成过程，极有可能是这3个杨属物种呈现间断分布格局与物种分化的关键成因。