AUTHOR=Zhao Yu-Juan , Yin Gen-Shen , Pan Yue-Zhi , Tian Bo , Gong Xun 

TITLE=Climatic Refugia and Geographical Isolation Contribute to the Speciation and Genetic Divergence in Himalayan-Hengduan Tree Peonies (Paeonia delavayi and Paeonia ludlowii)

JOURNAL=Frontiers in Genetics

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2020.595334

DOI=10.3389/fgene.2020.595334

ISSN=1664-8021

ABSTRACT=<p>Himalaya and Hengduan Mountains (HHM) is a biodiversity hotspot, and very rich in endemic species. Previous phylogeographical studies proposed different hypotheses (vicariance and climate-driven speciation) in explaining diversification and the observed pattern of extant biodiversity, but it is likely that taxa are forming in this area in species-specific ways. Here, we reexplored the phylogenetic relationship and tested the corresponding hypotheses within <italic>Paeonia</italic> subsect. <italic>Delavayanae</italic> composed of one widespread species (<italic>Paeonia delavayi</italic>) and the other geographically confined species (<italic>Paeonia ludlowii</italic>). We gathered genetic variation data at three chloroplast DNA fragments and one nuclear gene from 335 individuals of 34 populations sampled from HHM. We performed a combination of population genetic summary statistics, isolation-with-migration divergence models, isolation by environment, and demographic history analyses. We found evidence for the current taxonomic treatment that <italic>P</italic>. <italic>ludlowii</italic> and <italic>P</italic>. <italic>delavayi</italic> are two different species with significant genetic differentiation. The significant isolation by environment was revealed within all sampled populations but genetic distances only explained by geographical distances within <italic>P</italic>. <italic>delavayi</italic> populations. The results of population divergence models and demographic history analyses indicated a progenitor–derivative relationship and the Late Quaternary divergence without gene flow between them. The coalescence of all sampled cpDNA haplotypes could date to the Late Miocene, and <italic>P</italic>. <italic>delavayi</italic> populations probably underwent a severe bottleneck in population size during the last glacial period. Genetic variation in <italic>Paeonia</italic> subsect. <italic>Delavayanae</italic> is associated with geographical and environmental distances. These findings point to the importance of geological and climatic changes as causes of the speciation event and lineage diversification within <italic>Paeonia</italic> subsect. <italic>Delavayanae</italic>.</p>