Abstract
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.
Highlights
Understanding intercontinental disjunction patterns is among the main objectives of biogeography (Cox et al, 2016; Costa et al, 2020; Namgung et al, 2021)
The results indicated that all four species had typical cp genomes consisting of large single copy (LSC) and small single copy (SSC) regions and two inverted repeat (IR) copies, which are typically referred to as IRa and IRb. The pseudogene ycf 1 (IRb)
E. latifolius had a large number of base pairs in the SSC (18,581 bp), whereas the IR in E. macropterus comprised 26,709 bp (Figure 1)
Summary
Understanding intercontinental disjunction patterns is among the main objectives of biogeography (Cox et al, 2016; Costa et al, 2020; Namgung et al, 2021). Such disjunctions and fragmentations have resulted from continental drift, the formation of the Bering land bridge, the formation of deserts and lakes, and global climatic oscillations during the Cenozoic era (Ickert-Bond and Wen, 2006; Liao et al, 2007; Nie et al, 2008; Kim et al, 2015; Kim et al, 2017). Uniloculares the temperate regions of eastern North America and East Asia (Wen, 1999; Xiang et al, 2000; Wen, 2001), western North America and southern Europe (Wen and Ickert-Bond, 2009; Mao et al, 2010), and eastern and western North America (Xiang et al, 1998) have received much attention (Xiang et al, 1998; Wen, 1999; Deng et al, 2015; Kim et al, 2017; Song et al, 2020). Less emphasis has been placed on understanding the disjunction between East and West Asia (Song et al, 2020)
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