Phylogenetic Relationship And Population Genetic Structure Of Quercus Chungii And Q.championii

Quercus championii Benth.and Q.chungii F.P.Metcalf belong to Quercus section Cyclobalanopsis,Fagaceae.The two species are precious hardwood trees in southern China,and they are also the key canopy tree in regional subtropics evergreen broadleaved forests.Meanwhile,the two species are considered sister species due to the similar in morphological characteristic,but lack of molecular evidence to support them now.Therefore,understanding the historical distribution dynamics,phylogenetic relationship,population genetic patterns and evolutionary history of Q.championii and Q.chungii not only is theoretical basis for make its genetic resources protection,development and utilization strategies,but also is uesful to reveals the migration and dispersal of species in south China.In this study,we integrated(species distribution models（SDM）,Restriction site Associated DNA Sequencing（RADseq）and Simple Sequence Repeats（SSR）genotyping to reveal distribution dynamics,phylogenetic relationship,and population genetic structure of Q.championii and Q.chungii.These results were summarized below:（1）Phylogenetic relationship of Q.championii and Q.chungii,and the distributions of variations on their genomeBased RADseq data,a total of 11 species（27 samples）that including Q.championii,Q.chungii and other closely related species were used to reconstruction the phylogenetic trees using maximum likelihood and Bayesian methods.Both ML and BI trees gave the consistent tree topography showing that Q.championii and Q.chungii are not sister species,and genetic far from each other.Quercus chungii cluster with Q.austrocochinchiensis,Q.rex,Q.kerrii,Q.hypophaea and Q.delavayi;Q.championii cluster with Q.gilva and Q.sichourensis.About 80%RADseq loci can be mapped to a unique position on the 12 pseudochromosomes as well as 360 scaffolds of Q.robur.RADseq loci were widespread in genome,and the number of RADseq loci on chromosomes was positively correlated with chromosome length.The density of RADseq loci in gene region is large than non-gene region.（2）Distribution dynamics and niche differentiation of Q.championii and Q.chungiiA total of 30 and 25 occurrence sites for Q.championii and Q.chungii,respectively,were collected.The potential distributions of Q.championii and Q.chungii at present period were estimated using a maximum entropy model.Twenty random repetitive model tests all gave a higher Area Under Curve value（AUC>0.85）and lower variable coefficient for Q.championii and Q.chungii,which indicates that the model performs well.Predicted distribution is roughly consistent with the natural distribution of Q.championii and Q.chungii.Quercus chungii is widespread in Wuyi Mountain,Nanling Mountain and Xuefeng Mountain.The distribution of Q.championii is fragment distribution in the mountain region of south China.The most important restriction factor for the distribution of Q.championii is annual precipitation,and for Q.chungii is precipitation of driest month.The niches of Q.championii and Q.chungii were significantly different.（3）Population genetic structure of Q.chungiiA total of 188 individuals from 11 populations of Q.chungii were genotyped.We detected 56 alleles from selected nine SSR loci using ARLEQUIN.The A_Rand H_Evalues of populations were 2.63–3.32 and 0.46–0.67,respectively.The genetic differentiation among populations(F_ST)ranged from 0.02–0.32,and it is significantly correlated to the geographic distances（r=0.68）.Bayesian clustering analysis using STRUCTURE showed that a widespread genetic admixture in Q.chungii populations.The genetic diversity of populations from the Nanling Mountains was much higher than that from the eastern or the western regions of the species distribution.Furthermore,populations of Q.chungii in the Nanling Mountains have had suitable and steady habitats since the Last Glacial Maximum（LGM）.All these evidences suggested that Nanling Mountains and the adjacent area were a important glacial refugia of Q.chungii during the LGM period.Based on least cost path approaches,we found that the Nanling Mountains was the dispersal corridors for Q.chungii from the western to the eastern in both the present and the LGM periods.（4）Spatial genetic pattern and evolutionary history of Q.championiiA total of 56 individuals from 19 populations of Q.championii w ere genotyped using RADseq.The final datasets contained 5207 Single nucleotide polymorphism（SNP）.Four distinct lineages in Q.championii corresponding to its geographical distribution were resloved.The highest genetic admixture and genetic diversity were detected in group Hainan（HN）.Genetic differentitation among groups HN and Taiwan（TW）was highest(F_ST=0.116),while groups Southeast China（SE）and Southwest China-Northern Vietnam（SW）were the lowest(F_ST=0.034).Our DIYABC simulation inferred that Q.championii was originated from Southwest China-Northern Vietnam,then dispersed to Hainan Island and Southeast China in turn.Land bridges during glacial periods may have allowed Q.championii to colonize the islands.Climate warming during interglacial period contribute to species spread from southwest China to southeast China.Environmental variables also likely contributed to the genetic patterns observed in Q.championii.We found that isothermality was most strongly associated with genetic variation in the Q.championii populations.We identified genes regulating vegetative and reproductive organ development as important for the adaptation of Q.championii to heterogeneous environments.In summary,this study revealed that:1)Phylogenetic relationship between Q.championii and Q.chungii is not very close,and they are not sister species,and the niches of they are significantly different;2)Nanling Mountains served as dispersal corridor for the two species during the glacial period;3)Land bridges between mainland and costal islands in the Pleistocene contributed to flora assembly on the continental islands of South China.A cross province national nature reserve connecting the East to the West in Nanlin Mountain should be established,which can efficently safeguard the integrity of the vast forests in this area and enable the dispersal corridor for the regional biota.