Rapid Intraspecific Diversification of the Alpine Species Saxifraga sinomontana (Saxifragaceae) in the Qinghai-Tibetan Plateau and Himalayas.

Yan Li,Shi-Long Chen,Qing-Bo Gao,Zhuo-Ma Gengji,Zhi-Hua Wang,Liu-Kun Jia

doi:10.3389/fgene.2018.00381

Abstract

An increasing number of phylogeographic studies have been conducted for plant species in the Qinghai-Tibetan Plateau (QTP) and its flanking mountains. However, these studies have mainly focused on the determination of glacial refugia and routes of inter-/post-glacial expansions. Rapid intraspecific diversification of plants in this region have not been thoroughly discussed. Herein, we investigate the effects of the Quaternary climate changes on population genetic structure and diversifications of a herbaceous alpine species, Saxifraga sinomontana, which may have an evolutionary time scale <5 million years in the QTP and Himalayan regions. Using a total of 350 individuals from 29 populations, we studied the evolutionary history of S. sinomontana by analyzing cpDNA trnL-trnF, rpl16 and nrDNA ITS sequences. A total of 89 haplotypes and 158 genotypes were detected for cpDNA and ITS sequences, respectively. Only a few haplotypes/genotypes were widespread, while an extremely large number of haplotypes/genotypes were restricted to single populations, which were scattered throughout the current geographical range of S. sinomontana. This suggests the existence of microrefugia of this species during the Quaternary glaciations. In addition, the relationships of the haplotypes/genotypes were almost completely not resolved by phylogenetic reconstruction. Combining characteristics in terms of high haplotype richness, large proportion of private haplotypes, and shallow haplotype divergence, we speculate that recent intraspecific diversification has occurred in S. sinomontana. Molecular clock analysis estimated that the onset diversification within S. sinomontana to be 1.09 Ma (95% HPD = 0.80–1.45), coinciding with the extensive Quaternary glaciations on the QTP which started ca. 1.17 Ma. The Quaternary climatic oscillations may have triggered rapid intraspecific diversification in this QTP-Himalayan species. However, large niche breadth, as well as introgression/hybridization between the studied species and its closely related sympatric saxifrages, may also played a role to some extent on the current genetic structure of S. sinomontana, which need to be further studied.

Highlights

Evolutionary diversifications are usually considered as one of the main mechanisms that accumulate high levels of plant biodiversity in mountainous regions (Hughes and Eastwood, 2006; Pennington et al, 2010; Hughes and Atchison, 2015)
An increasing number of plant phylogeographic studies have been conducted in the Qinghai-Tibetan Plateau (QTP) and its flanking mountains (e.g., Zhang et al, 2005; Meng et al, 2007; Wang L. et al, 2009; Opgenoorth et al, 2010; Wang et al, 2010; see review by Qiu et al, 2011)
The aims of these studies mainly focused on the determination of glacial refugia and routes of inter-/postglacial expansions

Summary

Introduction

Evolutionary diversifications are usually considered as one of the main mechanisms that accumulate high levels of plant biodiversity in mountainous regions (Hughes and Eastwood, 2006; Pennington et al, 2010; Hughes and Atchison, 2015). The driving factors that have triggered such diversifications could be extrinsic (e.g., orogeny and climate change) (Hoorn et al, 2010), intrinsic (e.g., innovation of novel traits, polyploidization, hybridization, and niche shifts), or a combination (Ebersbach et al, 2017b) Among these factors, orogenic events are proposed to have played a disproportionate contribution to plant diversifications in the QTP and HHM at generic, even higher taxonomic levels (e.g., Liu et al, 2006; Wang Y.-J. et al, 2009; Zhang et al, 2012, 2014; Favre et al, 2015, 2016; Ebersbach et al, 2017a,b; Xing and Ree, 2017).

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