Chloroplast phylogeographic patterns of Calligonum Sect. Pterococcus (Polygonaceae) in arid Northwest China
3 June 2015
WEN, Zhibin; Xu, Zhe; Zhang, Hongxiang; Feng, YingTo understand the impacts of past climatic change and geological events on the evolutionary history of Calligonum Sect. Pterococcus, including C. aphyllum, C. rubicundum and C. leucocladum, a total of 128 individuals from 14 populations mainly in arid Northwest China, were sampled. Two cpDNA intergenic spacer regions (rpl32-trnL and ycf6-psbM) were sequenced and 11 haplotypes were identified. The low levels of genetic differentiation for C. rubicundum (FST = 0.54317, p < 0.001) and C. aphyllum (FST = 0.55795), whereas that for C. leucocladum (FST = 0.95800, p < 0.001) was high, suggesting that varied geographic distributions and habitats among them. Analysis of molecular variance (AMOVA) revealed that most of the total genetic variations occurred among species (72.97%). Among eleven identified haplotypes, only H1 and H2 were shared between C. aphyllum and C. rubicundum, while nine were private among the three species. The eleven identified haplotypes were split into two major clades, but they did not yield three species-specific lineages. Calligonum Sect. Pterococcus were therefore not reciprocally monophyletic, more likely due to incomplete lineage sorting than hybridization. Mismatch distribution analysis suggested that only C. aphyllum experienced recent demographic expansion. Divergence time among the 11 haplotypes was estimated at between 2.84 Ma and 0.06 Ma. Within the two clades, haplotype divergence began in early Pleistocene and mainly occurred during the middle to late Pleistocene which was most likely triggered by Quaternary climatic oscillations and the enhancement of aridity.