Phylogeography Of Nitraria Roborowskii Based On CpDNA Sequences

Since Pleistocene, the global climate became cold and experienced periodic glacial period and post-placial period. This ancient climatic events could affect the distribution pattern of species. This impact could leave traces on the genetic structure of plants. Palynology data indicate that northwestern China experienced several periodic warm/moist to cold/dry cycles during the Quaternary. In addition, geomagnetism evidences suggest that desert in northwestern China has undergone violent expansion since the late Tertiary period. To understand the influence of climate oscillations and desert expansion on evolutionary processes of organisms in arid northwestern China, we selected Nitraria roborowskii to resolve it by examining the phylogeographic structure and demographic history. Through the field collection, we obtained total of 21 populations and 243 individuals cover almost N. roborowskii's sranges. Finally, we selected two chloroplast DNA(cpDNA) intergenic spacers(pabA-trn H and rpl32-trn L) to study the genetic structure and demographic history of N. roborowskii and assess whether the geographical pattern and genetic variation correspond to the climate fluctuations and deserts expansion during the Pleistocene in northwestern China.A total of 20 haplotypes were indentified on the variation of pabA-trnH and rpl32-trnL. High levels of genetic diversity and significant phylogeographical signals were detected. We suggest the desert expansion caused fragmentation distribution of N. roborowskii and resulted in restricted gene flow among populations. And the result of demographic history revealed population expansion after glacial period. Through the genetic analysis, we suggested that N. roborowskii origined from the Tarim Basin and migrated to the Alxa Desert though the Hexi Corridor, and we speculated Shandan Country as the refugium or center of genetic diversity of N. roborowskii.