New insight into the phylogeographic pattern ofLiriodendron chinense(Magnoliaceae) revealed by chloroplast DNA: east–west lineage split and genetic mixture within western subtropical China

Aihong Yang,Yongda Zhong,Yanqiang Li,Shujuan Liu,Faxin Yu,Lipan Liu,Tengyun Liu

doi:10.7717/peerj.6355

Abstract

BackgroundSubtropical China is a global center of biodiversity and one of the most important refugia worldwide. Mountains play an important role in conserving the genetic resources of species. Liriodendron chinense is a Tertiary relict tree largely endemic to subtropical China. In this study, we aimed to achieve a better understanding of the phylogeographical pattern of L. chinense and to explore the role of mountains in the conservation of L. chinense genetic resources.MethodsThree chloroplast regions (psbJ-petA, rpl32-ndhF, and trnK5’-matK) were sequenced in 40 populations of L. chinense for phylogeographical analyses. Relationships among chloroplast DNA (cpDNA) haplotypes were determined using median-joining networks, and genetic structure was examined by spatial analysis of molecular variance (SAMOVA). The ancestral area of the species was reconstructed using the Bayesian binary Markov Chain Monte Carlo (BBM) method according to its geographic distribution and a maximum parsimony (MP) tree based on Bayesian methods.ResultsObvious phylogeographic structure was found in L. chinense. SAMOVA revealed seven groups matching the major landscape features of the L. chinense distribution area. The haplotype network showed three clades distributed in the eastern, southwestern, and northwestern regions. Separate northern and southern refugia were found in the Wu Mountains and Yungui Plateau, with genetic admixture in the Dalou Mountains and Wuling Mountains. BBM revealed a more ancient origin of L. chinense in the eastern region, with a west–east split most likely having occurred during the Mindel glacial stage.DiscussionThe clear geographical distributions of haplotypes suggested multiple mountainous refugia of L. chinense. The east–west lineage split was most likely a process of gradual genetic isolation and allopatric lineage divergence when the Nanling corridor was frequently occupied by evergreen or coniferous forest during Late Quaternary oscillations. Hotspots of haplotype diversity in the Dalou Mountains and Wuling Mountains likely benefited from gene flow from the Wu Mountains and Yungui Plateau. Collectively, these results indicate that mountain regions should be the main units for conserving and collecting genetic resources of L. chinense and other similar species in subtropical China.

Highlights

Climate oscillations during the Late Tertiary and Quaternary are believed to have had profound influences on species variation and extinction and to have shaped the population structures of relict species (Hewitt, 2000, 2004)
Thirty-seven haplotypes were found in L. chinense, and six haplotypes were identified in L. tulipifera
East–west lineage split and the role of the Nanling Mountains By investigating chloroplast DNA (cpDNA) sequence variation, an obvious west–east lineage split across subtropical China was found for L. chinense, and this L. chinense west–east genetic divergence was further shown by the phenotypic divergence between the eastern and western regions, such as divergence in petal color and lobed leaf number (Hao et al, 1995)

Summary

Introduction

Climate oscillations during the Late Tertiary and Quaternary are believed to have had profound influences on species variation and extinction and to have shaped the population structures of relict species (Hewitt, 2000, 2004). 34 °N) and the tropical south (≤22 °N) and between 99 °E and 123 °E, is characterized by evergreen broad-leaved forests (Wu & Wu, 1998; Wang, Kent & Fang, 2007) This area consists mainly of hills and low mountains, many of which have been identified as Chinese centers of plant endemism (López-Pujol et al, 2011), and it has provided important refugia for terrestrial tree species that were not available in other regions at the same latitude. The subtropical region in southern Europe and eastern North America was largely occupied by the Mediterranean Sea (Taberlet et al, 1998) and the Gulf of Mexico (Guo, Ricklefs & Cody, 1998), respectively, and mountains have played an important role in conserving the genetic resources of species and have served as refugia for paleoendemic species (Hewitt, 2000; López-Pujol et al, 2011).

Objectives

Methods

Results

Discussion

Conclusion