Phylogeography and evolution of two closely related oak species (Quercus) from north and northeast China

Orographic and climatic influences during the Pleistocene have had a crucial role on interspecific divergence and population demography during speciation. However, associations between demographic histories of closely related species and related climatic events, especially in north and northeast China, are still underexplored. Genetic analyses with four chloroplast DNA and two nuclear genes and species distribution modeling were used for two closely related oak species (Quercus liaotungensis and Quercus mongolica) to test if their interspecific divergence and phylogeographical histories were possibly related to the Pleistocene-era climatic events. Potential divergence of the two oak species was estimated at about 0.92-2.15 Ma. Species distribution models and genetic data showed varying phylogeographical histories and spatial population structures between the two oaks, leading to different patterns of interspecific gene flow between the chloroplast and nuclear genes. The results indicate that speciation event between the two species is recent and may have been triggered by geological and climatic fluctuations linked to the upheavals of the Qinghai-Tibetan Plateau at the Pliocene/Pleistocene boundary. The two closely related oaks possess varying population demography during the interglacial-glacial climatic oscillations of the Quaternary, probably due to the various niche adaptations among different distribution ranges across their species trajectories.