Study On Population Genetics Structure And Phylogeography Of Quercus Serrata And Q. Serrata Var. Brevipetiolata (Quercus)

Oak become a model species to study evolution and global ecological climate change with diverse variety and widely distribution in recent years. Quercus serrata and Quercus serrata var. brevipetiolata are important forest tree species belonging to Quercus (Fagaceae). They have their own centralized distribution area and the overlapping area with the possibility of interspecific hybridization, are good materials to study genetic variation and differentiation between species. This study focused on the population genetic structure and phylogeography of 45 populations (8 Q. serrata and 37 Q. serrata var. brevipetiolata) from across the geographic range of the plants to probe into the genetic diversity and genetic structure, to research the relationship between them, and to suggest the potential of glacial refuges. The main conclusions are as follows:(1) Q. serrata and Q. serrata var. brevipetiolata populations (45 populations) with 433 individuals were analyzed based on three cpDNA (ycfl, psbA-trnH, matK). The genetic results indicated rich genetic diversity of them, Hd= 0.902 and π= 0.00170 were all high. Haplotype diversity of Q. serrata (Hd= 0.733) is lower than Q. serrata var. brevipetiolata (Hd = 0.874), while nucleotide diversity of Q. serrata (π= 0.00213) is higher than Q. serrata var. brevipetiolata (π= 0.00149).22 haplotype were found based on cpDNA, in which H1, H4, H5 is shared. H5 and H6 were widely distributed in the range. At the same time, H2 and H3 is unique to Q. serrata. The rest of the haplotype (H6-H22) is unique to Q. serrata var. brevipetiolata. AMOVA showed that the genetic differentiation is very high (Q. serrata:Fst= 0.995; Q. serrata var.brevipetiolata:FST= 0.942). Most of the genetic variation (Q. serrata accounted for 99.470%; Q. serrata var. brevipetiolata accounted for 94.230%) existed among populations. In addition, NETWORK analysis and the distribution of haplotype showed the Qinling mountains with much unique haplotypes and high haplotype diversity may be possible refuges during the glacial period. The border area of Zhejiang, Anhui and Jiangsu provinces in East China with ancient haplotype (H5 and H6) and unique haplotype (H8, H12 and H13) may be another possible refuges for Q. serrata var. brevipetiolata. Besides, northwest of Hunan and west of Hubei maybe another refuges for Q. serrata var. brevipetiolata.(2) A total of 757 individuals of Q. serrata and Q. serrata var. brevipetiolata were investigated to analyze the genetic diversity and genetic structure based on eight nSSR markers. The genetic results indicated rich genetic diversity, He= 0.465,I= 0.730, PPL= 83.89% for all populations. Q. serrata:He= 0.380, Ho= 0.334,I= 0.788, PPL= 95.31%; Q. serrata var. brevipetiolata:He= 0.348, Ho= 0.290,I= 0.718, PPL= 81.42%). Analysis of molecular variance (AMOVA) showed that genetic variation mainly existed within populations (Q. serrata account for 86.170%; Q. serrata var. brevipetiolata account for 77.580%). The two species were plotted based on the Bayesian clustering analysis (Structure), and gene flow existed among these populations (Nm= 1.031). No correlation was found between the genetic distance and geographical distance (Q. serrata:P= 0.196; Q. serrata var. brevipetiolata:P= 0.814). The rich genetic diversity and genetic structure of Q. serrata and Q. serrata var. brevipetiolata based on the nSSR markers, which were related to complex population dynamics, anemophilous characteristics and its habitat conditions. The genetic structure of Q. serrata and Q. serrata var. brevipetiolata were probably derive from the heterogeneity of species habitats and fragmented environments caused by current human influences.(3) Combined with cpDNA and SSR markers, we get different geographical patterns of phylogeography. The cpDNA showed greater genetic differentiation between the two species with less haplotype sharing and different distribution of haplotype respective. We hypothesized that it is consist with refuges in the late glacial period and population dynamics postglacial. SSR results showed that the more gene flow between the two species together with low genetic differentiation showed that neutral nuclear gene flow mediated by pollen influenced by reproductive isolation is small, and the two species did not form a complete reproductive isolation.