AUTHOR=Li MinJie , Xie DengFeng , Xie Chuan , Deng YiQi , Zhong Yan , Yu Yan , He XingJin 

TITLE=A Phytogeographic Divide Along the 500 mm Isohyet in the Qinghai-Tibet Plateau: Insights From the Phylogeographic Evidence of Chinese Alliums (Amaryllidaceae)

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00149

DOI=10.3389/fpls.2019.00149

ISSN=1664-462X

ABSTRACT=<p>The Qinghai-Tibet Plateau (QTP) has been biogeographically divided into the eastern monsoonal and the western continental climatic zones along the 500 mm isohyet. However, this biogeographic hypothesis has been rarely tested using a phylogeographic approach. The members of the genus <italic>Allium</italic> subgenus <italic>Cyathophora</italic> coincidentally distribute across this biogeographical divide. Intriguingly, <italic>Allium fasciculatum</italic> of subgenus <italic>Amerallium</italic> co-occurs in the distribution range of subgenus <italic>Cyathophora</italic>. To illuminate the role of this biogeographic divide on the genetic divergence, we genotyped 466 individuals of 52 populations of subgenus <italic>Cyathophora</italic> and 110 individuals of 19 populations of <italic>A. fasciculatum</italic> using three chloroplast DNA fragments, whole nrITS and nine nuclear microsatellite loci, supplemented with the present environmental space and paleo-distribution modeling. Our phylogeographical evidence recovered the concordant east–west genetic breaks both for subgenus <italic>Cyathophora</italic> and <italic>A</italic>. <italic>fasciculatum</italic> along the 500 mm isohyet. The divergence time estimations and environmental niche differentiations suggested this east–west genetic breaks could have been triggered by the climatic-induced vicariance during the early Pleistocene. Noticeably, this split within subgenus <italic>Cyathophora</italic> could have been deepened by the morphological vicariance from the eastern umbel to the western spicate, while that within <italic>A. fasciculatum</italic> could have been obscured due to the pollen flows from the east to west caused by the postglacial expansion. The genetic structures and ecological niche modelings (ENMs) recovered the distinct responses to the Quaternary climatic oscillations for species constricted to different climatic zones, further highlighting the profound effect of the climatic differences and tectonic uplifts on the genetic diversification. Overall, our findings offer strong evidence for the existence of a biogeographic divide between the eastern monsoonal and the west continental climatic zones of the QTP nearly along the 500 mm isohyet.</p>