Abstract
Liriodendron is a Tertiary period relic tree genus with a typical East Asian and North American disjunction distribution pattern. As an angiosperm base group of trees, Liriodendron provides a valuable resource for the study of evolution processes. Here, we reconstruct the phylogeny and population genetic structure of Liriodendron based on the restriction site-associated DNA sequencing (RAD-Seq) of a wide collection of individuals from 16 populations. Our results reveal a clear phylogenetic break between L. chinense and L. tulipifera and obvious genetic divergence between the eastern and western populations of L. chinense, which are consistent with the patterns of geographical distributions. The phylogeographic history and long-term geographical isolation of the genus may be responsible for this pattern. Furthermore, a closer relationship was found between L. tulipifera and the eastern populations of L. chinense, indicating the ancient phylogeny of L. chinense in this area. The results of this study will aid in the development of scientific strategies for the conservation and utilization of the Liriodendron germplasm.
Highlights
East Asian and North American disjunction is a long-term concern [1,2,3,4,5]
We argue that the results of restriction site-associated DNA sequencing (RAD-Seq) may reflect a neutral evolution history of Liriodendron, and the genetic demarcations between the Eastern China (EC) and Western China (WC) L. chinense populations suggest a background genetic structure inherited from its long history
A recent study on 40 populations of L. chinense revealed an east–west split over the whole range of L. chinense using three chloroplast DNA (cpDNA) fragments [45]; this is coincidently consistent with the present results revealed by RAD-Seq data from the whole genome
Summary
East Asian and North American disjunction is a long-term concern [1,2,3,4,5]. As a relic tree genus, Liriodendron (Magnoliaceae) was once widespread in the Northern Hemisphere and comprised several species in the Cretaceous and Tertiary periods [6]. L. tulipifera is predominantly distributed in the east of the Mississippi river, from the gulf coast to southern Canada, and is a major reforestation species in the USA [6,11,12]. These two species are geographically isolated by the Pacific Ocean, they are morphologically similar and cross-fertile [13]. The Liriodendron was pivotal to the evolution of flowering plants [14] It is an ideal plant for population genetics and phylogenetic studies [15]
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