Data from: Phylogeography of Sophora moorcroftiana supports Wu’s hypothesis on the origin of Tibetan alpine flora

Wu hypothesized that the Tibetan flora originated mostly from the paleotropical Tertiary flora in the Hengduan Mountains by adapting to the cold and arid environments associated with the strong uplift of the Qinghai-Tibet Plateau (QTP). Here, we combine the phylogeographic history of Sophora moorcroftiana with that of S. davidii to explore the speciation of S. moorcroftiana to test this hypothesis. We collected 151 individuals from 17 populations and sequenced two chloroplast fragments and the internal transcribed spacer of rDNA. Five chlorotypes and nine ribotypes were detected but no significant phylogeographic structure was revealed. The integrated results of phylogeographic studies of these two species clearly support the progenitor-derivative relationship between them. We infer that the western peripheral population of S. davidii migrated westwards from the Hengduan Mountains to the middle reaches of the Yarlung Zangbo River and differentiated from its ancestor in the process of adaptation to increasingly cold and arid environments with the uplift of the QTP and finally evolved into S. moorcroftiana during the Late Pliocene. In addition, our findings shed light on the idea that natural selection, as imposed by climate differentiation (especially mean diurnal range and precipitation seasonality), directly drove this peripatric speciation event after geographic isolation. The speciation of S. moorcroftiana is a strong case supporting Wu’s hypothesis about the origin of Tibet’s flora.

吴提出假说，藏区植物区系主要起源于横断山区的古热带第三纪植物区系，类群通过适应伴随青藏高原（Qinghai-Tibet Plateau, QTP）强烈隆升所形成的寒冷干旱环境得以演化。本研究结合砂生槐（Sophora moorcroftiana）与苦参（Sophora davidii）的谱系地理学历史，旨在探讨砂生槐的物种形成过程，以验证上述假说。本研究从17个种群中共采集151份个体样本，对两段叶绿体片段以及核糖体DNA内转录间隔区（internal transcribed spacer of rDNA）进行了测序。研究共检测到5种叶绿体单倍型（chlorotype）与9种核糖体单倍型（ribotype），但未发现显著的谱系地理学结构。对这两个物种的整合谱系地理学分析结果，明确支持二者之间的祖先-衍生类群关系。本研究推断，苦参的西部边缘种群从横断山区向西迁移至雅鲁藏布江中游流域，在伴随青藏高原隆升、逐步适应寒冷干旱环境的过程中与其祖先类群产生分化，并最终于上新世晚期演化形成砂生槐。此外，本研究结果佐证了如下观点：地理隔离形成后，气候分异（尤其是昼夜温差均值与降水季节性）所施加的自然选择，直接驱动了此次边域成种事件。砂生槐的物种形成过程，为验证吴提出的藏区植物区系起源假说提供了强有力的实证支持。