Phylogeographic evidence for a link of species divergence of Ephedra in the Qinghai-Tibetan Plateau and adjacent regions to the Miocene Asian aridification.

The Qinghai-Tibetan Plateau (QTP) has become one of the hotspots for phylogeographical studies due to its high species diversity. However, most previous studies have focused on the effects of the Quaternary glaciations on phylogeographical structures and the locations of glacial refugia, and little is known about the effects of the aridization of interior Asia on plant population structure and speciation. Here the chloroplast DNA (cpDNA) trnT-trnF and trnS-trnfM sequences were used to investigate the differentiation and phylogeographical history of 14 Ephedra species from the QTP and northern China, based on a sampling of 107 populations. The phylogeographical analysis, together with phylogenetic reconstruction based on combined four cpDNA fragments (rbcL, rpl16, rps4, and trnS-trnfM), supports three main lineages (eastern QTP, southern QTP, and northern China) of these Ephedra species. Divergence of each lineage could be dated to the Middle or Late Miocene, and was very likely linked to the uplift of the QTP and the Asian aridification, given the high drought and/or cold tolerance of Ephedra. Most of the Ephedra species had low intraspecific variation and lacked a strong phylogeographical structure, which could be partially attributed to clonal reproduction and a relatively recent origin. In addition, ten of the detected 25 cpDNA haplotypes are shared among species, suggesting that a wide sampling of species is helpful to investigate the origin of observed haplotypes and make reliable phylogeographical inference. Moreover, the systematic positions of some Ephedra species are discussed.

青藏高原由于其物种多样性高，已成为系统地理学研究的热点地区之一。然而，以往的大多数研究都集中在第四纪冰川作用对系统地理结构和冰川避难所位置的影响上，而对于亚洲内陆干旱化对植物种群结构和物种形成的影响知之甚少。在此，基于对107个种群的采样，利用叶绿体DNA（cpDNA）的trnT - trnF和trnS - trnfM序列来研究青藏高原及中国北方14种麻黄属植物的分化和系统地理历史。系统地理分析以及基于四个组合的cpDNA片段（rbcL、rpl16、rps4和trnS - trnfM）的系统发育重建，支持这些麻黄属植物的三个主要谱系（青藏高原东部、青藏高原南部和中国北方）。每个谱系的分化可追溯到中新世中期或晚期，鉴于麻黄属植物具有高度的耐旱和/或耐寒性，这很可能与青藏高原的隆升和亚洲干旱化有关。大多数麻黄属植物种内变异低，缺乏明显的系统地理结构，这可能部分归因于克隆繁殖和相对较近的起源。此外，在检测到的25种cpDNA单倍型中，有10种在物种间共享，这表明广泛的物种采样有助于研究观察到的单倍型的起源，并做出可靠的系统地理推断。此外，还讨论了一些麻黄属植物的系统位置。