Table_4_Disjunction and Vicariance Between East and West Asia: A Case Study on Euonymus sect. Uniloculares Based on Plastid Genome Analysis.DOCX

Scientists have long been captivated by biogeographic disjunctions, and disjunctions between East Asia and North America have been particularly well-studied at the genus and family levels. By contrast, disjunctions between eastern and western Asia have received less attention. Euonymus L. is taxonomically divided into two sections based on the number of cells in anthers as follows: E. sect. Uniloculares has one-celled anthers and occurs mainly in Asia, whereas E. sect. Biloculares has two-celled anthers and is distributed globally. We used Illumina sequencing to investigate the genomes of four species in sect. Uniloculares. The chloroplast (cp) genomes are highly conserved (157,290–158,094 bp). Pseudogenisation of ndhF and intron loss in rps16 was detected. Based on the cp genomes of the four species of E. sect. Uniloculares, we propose a novel hypothesis of disjunction between eastern and western Asia. Biogeographic reconstruction and molecular dating revealed that sect. Uniloculares separated from its sect. Biloculares forebears 4.0 Mya during the Pliocene era. The radial diversification of sect. Uniloculares from East Asia and the establishment of the western Asian clade during the Pleistocene era (1.9 Mya) were the results of both dispersal and vicariance, making the section the youngest diverged clade conforming to age estimation. The centre of origin of sect. Uniloculares was determined to be in East Asia. Disjunctions and diversification between eastern and western Asia in sect. Uniloculares are thought to have been caused by changes in monsoon patterns, temperature variations, and the emergence of the Gobi Desert.

长期以来，科学家们一直对生物地理间断分布（biogeographic disjunctions）现象着迷，其中东亚与北美的间断分布模式在属和科的分类层级上得到了尤为深入的研究。相比之下，东亚与西亚之间的间断分布却较少受到关注。卫矛属（Euonymus L.）可根据花药的细胞数目被划分为两个组，具体如下：单室卫矛组（E. sect. Uniloculares）具单室花药，主要分布于亚洲；双室卫矛组（E. sect. Biloculares）具双室花药，全球范围内均有分布。本研究采用Illumina测序技术，对单室卫矛组的4个物种的基因组展开了分析。该类群的叶绿体（chloroplast, cp）基因组高度保守，长度介于157290至158094碱基对（bp）之间。研究检测到ndhF基因发生假基因化（pseudogenisation），以及rps16基因出现内含子丢失（intron loss）现象。基于单室卫矛组4个物种的叶绿体基因组数据，我们提出了关于东亚与西亚间断分布的全新假说。生物地理重建（biogeographic reconstruction）与分子年代测定（molecular dating）结果显示，单室卫矛组与其双室卫矛组的祖先类群在400万年前的上新世（Pliocene era）发生分化。单室卫矛组从东亚出发的辐射分化，以及更新世（Pleistocene era，190万年前）西亚支系（western Asian clade）的形成，均为扩散（dispersal）与隔离分化（vicariance）共同作用的结果，该组也成为符合年代估算结果的最年轻分化支系。单室卫矛组的起源中心被确定为东亚地区。单室卫矛组东亚与西亚之间的间断分布与分化，被认为是由季风模式改变、温度波动以及戈壁沙漠的形成共同驱动的。