Phylogeography of Quercus glauca (Fagaceae), a dominant tree of East Asian subtropical evergreen forests, based on three chloroplast DNA interspace sequences

Historical geoclimatic events have shaped the distribution patterns and intraspecific divergence of plants. Numerous phylogeographical studies in China have focused on the Qinghai-Tibetan Plateau and surrounding areas due to the complex topography and high species diversity, but the impact of Neogene events and Quaternary climatic change on the flora of subtropical China remains poorly understood. Quercus glauca, a widespread tree of East Asian subtropical evergreen forests, has rich fossil records dating back to the Neogene, and it provides a good model to explore the impact of paleogeoclimate changes on East Asian subtropical forests. We used three chloroplast DNA (cpDNA) intergenic spacer regions and ecological niche modeling (ENM) to analyze the divergence pattern and demographic history of Q. glauca in China and Japan. A total of 33 haplotypes were detected. The phylogenetic analysis revealed two major haplotype lineages (Southwest China vs. Southeast China and East China Sea). The limited dispersal ability of seeds and complex topography resulted in the high total, inter- and intrapopulation haplotype diversity. The fossil-constrained BEAST analysis revealed a lineage diversification in the late Miocene-Pliocene. The formation of complex topography changes since Miocene in east Himalaya and adjacent area might be the key factor that triggered the intraspecific divergence of Q. glauca. Haplotype spatial distribution, ENM, mismatch distribution, and neutrality tests suggest that Q. glauca in Southeast China experiences expansion, and the current distribution in region III might be shaped by southward expansion from regions I and II after last glacial maximum (LGM). Regions I and II were the potential glacial refugia of Q. glauca.