Phylogeography Of Ribes Meyeri (Saxifragaceae) Based On CpDNA Sequences

The climatic oscillations and geological events have seriously affected the range distribution andcurrent diversity of all plants occurring over the world especially those in the temperate regions.Phylogeography was developed to elucidate these patterns, processes and factors based on the molecularsignals, for example, identifying the glacial refugia and tracing the postglacial recolonizations. In this study,to investigate the genetic diversity and influence of climate oscillations on evolutionary processes oforganisms in northwest China, we selected Ribes meyeri and examined the phylogeographic structure andthe response to the Quaternary climatic oscillations of this species. Using two chloroplast DNA (cpDNA)intergenic spacers (psbA-trnH and psbK-psbI), a phylogeographical study of Ribes meyeri with237individuals from30populations was performed to assess whether the geographical pattern and geneticvariation correspond to the climate fluctuations and deserts expansion during the Pleistocene innorthwestern China.A total of20haplotypes were identified on the basis of nucleotide variation, and it reveals high geneticdiversity (HT=0.857) and significant phylogeographical signals (GST=0.613, NST=0.855). Geneticdifferentiation among populations within groups was high, suggesting that there was restricted gene flowamong populations in groups. In this study, two geographical regions were defined:(1) Western region (theAltai and Tianshan Mountains), and (2) Eastern region (the Qilian and Helan Mountains). The dominanthaplotypes, located at internal nodes and derived from an extinct ancestral haplotype in the network, werefound to be distinct between Western and Eastern population groups of the species. According to our IMaresult, the split of these groups occurred at approximately495ka BP, coincident with the Pleistocenemaximum glacial stage in this area. We speculate that the climatic oscillations during the Quaternary, weredetermining factors contributing to the lineage split. Unimodal mismatch distributions were obtained forboth of the groups, suggesting postglacial range expansions were identified for these phylogeographiclineages. In consideration of their relatively moist habitat conditions and high levels of genetic diversity,the populations of BEJ and ZS are inferred to have been refugial locations for the Western group duringglacial cold-dry conditions. Similarly, the populations of YC and YZ within the eastern group are alsoindicated as likely refugia.