Phylogeographic History of Atraphaxis Plants in Arid Northern China and the Origin of A. bracteata in the Loess Plateau.

Zhe Xu,Ming-Li Zhang,James I Cohen,Dusan Gomory

doi:10.1371/journal.pone.0163243

Abstract

In China, species of Atraphaxis (Polygonaceae) primarily inhabit arid zones across temperate steppe and desert regions. The complex geologic history (e.g., expansion of deserts) and extreme climate shifts of the region appear to have played an important role in shaping the phylogeography of Atraphaxis. The present study focuses on species-level phylogeographic patterns of Atraphaxis in China, with the goal of determining the impact of past environmental changes, in northern China, on the evolutionary history of the genus. Five hundred and sixty-four individuals distributed among 71 populations of 11 species of Atraphaxis from across the geographic range of the genus were studied using sequence data from two plastid spacers, psbK-psbI and psbB-psbH. The results demonstrate that most chloroplast haplotypes are species-specific, except for some present among widespread species. The phylogeny of Atraphaxis was well structured, and molecular dating analyses suggest that the main divergence events occurred during the late Pliocene and Pleistocene (5.73–0.03 million years ago). The statistical dispersal-vicariance analysis (S-DIVA) results provide evidence that phylogeographic patterns for the genus were characterized by both vicariance events and regional dispersal. The presented data suggest that the rapid expansion of deserts and climatic changes in northern China during the late Pliocene and Pleistocene have driven the diversification and spread of Atraphaxis in the region. The expansion of the Tengger Desert provided appropriate conditions for the origin of A. bracteata. Additionally, a contact zone in the north of the Hexi Corridor was identified as having played a significant role as a migratory route for species in adjacent areas.

Highlights

The Pleistocene was characterized by extensive oscillations of the global climate that strongly affected the evolution and geographic distributions of organisms and communities [1,2]
Past climatic changes in northern China have resulted in modified ecosystems and species distributions [22]
The phylogeographic patterns of Atraphaxis are congruent with those previously described for other arid shrubs and small herbs, previous studies primarily focused on a single species and a particular geographic area in the arid regions of northern China [7,59,60]

Summary

Introduction

The Pleistocene was characterized by extensive oscillations of the global climate that strongly affected the evolution and geographic distributions of organisms and communities [1,2]. The eastern sandlands of this region are part of the “Mongolia Flora” and species that inhabit the sandlands are hypothesized to have primarily migrated from Mongolia and East Asia [18] Both increased aridification and range contraction and isolation during dry/cold episodes in glacial cycles might have played a major role in promoting population divergence and speciation in arid northern China. The present study aims to investigate these patterns, with the goal of providing a more comprehensive historical perspective on both the biota and geological evolution of species in the arid northern China To tackle this project, we employed cpDNA sequence data to infer genetic patterns and population responses of species of Atraphaxis to past environmental changes throughout arid northern China. This information will help determine the impact of past environmental changes, in northern China, on species of Atraphaxis

Material and Methods

Results

Discussion