Evolutionary And Historical Demography Of Oak Species Of Group Ilex Occurred In China

Quercus species are widely distributed in the world,they are common forest species and dominant species,which have important economic and ecological values.The species boundaries within oak species are undistinguished,and hybridization and/or introgression are frequent within these species.Furthermore,due to their evolutionary history is closely related to climate and environmental changes,they have been considered as model species for studying adaptive or local evolution and ecological speciation.Studies about oak species have been carried out very early in Europe and North America,especially in phylogeography and landscape genetics.Up to date,there are lots of researches about these two fields which utilized different kinds of molecular markers to speculate the different demographic history and patterns of genetic variation between oak species have been reported there.Although China has been considered as one of distribution centers of oak species in the world,there are few studies about oak species.In the present study,in order to demonstrate the impact of uplifting of Qinghai-Tibet Plateau and climate changes since Neogene on evolutionary history and patterns of genetic strcucture of oak species belong to Group Ilex,we used different kinds of molecular markers(including chloroplast DNA fragments,ITS and nuclear microsatellite loci)to indicate the evolutionary and population demography of oak species(including Quercus spinosa,Quercus aquifolioides,and Quercus rehderiana)occurred in East Himalaya-Hengduan mountains and adjacent regions.In addition,in order to test the phylogeographical hypothesis based on the results of temperate deciduous forests whether could be applied for depicting the results of evergreen tree species occurred in subtropical China,we also use a multidisciplinary approach to indicate the phylogeography and evolutionary history of Quercus spinosa occurred in this area.Our results and main conclusions are as follows:1.We determined the genetic structure and evolutionary history of alpine oak species(including Quercus spinosa,Quercus aquifolioides,and Quercus rehderiana)using both cytoplasmic-nuclear markers and ecological niche models(ENMs),and elucidated the impacts of climate oscillations and environmental heterogeneity on their population demography.Our results indicate there were mixed genetic structure and asymmetric contemporary gene flow within them.The ENMs revealed a similar demographic history for the three species expanded their ranges from the last interglacial(LIG)to the last glacial maximum(LGM),which was consistent with effective population sizes changes.Effects of genetic drift and fragmentation of habitats were responsible for the high differentiation and the lack of phylogeographic structure.Our results support that geological and climatic factors since Miocene triggered the differentiation,evolutionary origin and range shifts of the three oak species in the studied area and also emphasize that a multidisciplinary approach combining molecular markers,ENMs and population genetics can yield deep insights into diversification and evolutionary dynamics of species.2.The complex geography and climatic changes occurring in subtropical China during the Tertiary and Quaternary might have provided substantial opportunities for allopatric speciation.To gain further insight into these processes,we reconstruct the evolutionary history of Quercus spinosa,a common evergreen tree species mainly distributed in this area.Forty-six populations were genotyped using four chloroplast DNA regions and 12 nuclear microsatellite loci to assess genetic structure and diversity,which was supplemented by divergence time and diversification rate analyses,environmental factor analysis,and ecological niche modeling of the species distributions in the past and at present.The genetic data consistently identified two lineages: the western Eastern Himalaya-Hengduan Mountains lineage and the eastern Central-Eastern China lineage,mostly maintained by populations’ environmental adaptation.These lineages diverged through climate/orogeny-induced vicariance during the Neogene and remained separated thereafter.Genetic data strongly supported the multiple refugia(per se,interglacial refugia)or refugia within refugia hypotheses to explain Q.spinosa phylogeography in subtropical China.Quercus spinosa population structure highlighted the importance of complex geography and climatic changes occurring in subtropical China during the Neogene in providing substantial opportunities for allopatric divergence.