Study On Population Genetics And Demographic History Of The Three Closely Related Species Of Section Aegilops Occurred In China

The genus Quercus is the largest genus in Fagaceae.This genus includes a wide variety of plants mainly distributed in Northern Hemisphere.They are common forest species and dominant species with important economic and ecological value.In addition,the boundary among the species is indistinct;interspecific hybridization or introgression occurs frequently and its evolutionary history is closely related to climate and environmental changes.Therefore,it is also considered as a model for the study of adaptive evolution or ecological species formation.In this study,596 pairs of EST-SSR primers were designed.Total genomic DNA were extracted from 759 leaf samples in 44 natural populations of three closely related species of Section Aegilops distributed in China(336 individuals in 19 Quercus variabili populations,338 individuals in 20 Quercus acutissima populations and 85 individuals in 5 Quercus chenii populations).Then,all genomic DNA were amplified using 16 pairs of highly polymorphic primers.Finally,the sizes of all amplified product fragments were counted.After the analysis about population genetics,ABC and SDMs,the research explored the genetic structure and genetic diversity of the three species and predicted their possible evolutionary history and distribution pattern in order to reveal the level of genetic variation and response patterns of the three species.The results showed that there were 206 alleles in 16 SSR loci.The average observed heterozygosity(Ho)and the average expected heterozygosity(He)were 0.348 and 0.774,respectively.Each species had high genetic diversity(Q.variabilis: He = 0.710,Ho = 0.260,PIC = 0.681;Q.acutissima: He = 0.677,Ho = 0.369,PIC = 0.645;Q.chenii: He = 0.681,Ho = 0.599,PIC = 0.743).The analysis of molecular variance(AMOVA)results showed that each species had high proportions of intra-population variation(Q.variabili: 91.03%,Q.acutissima: 78.73% and Q.chenii: 94.55%).For all species,the analysis of molecular variance(AMOVA)results showed that the proportion of intra-population variation(68.72%)accounted for the majority.However,the proportions of inter-species variation and inter-population were 19.52%(FCT = 0.195)and 11.76%(FSC = 0.146).This also indicated that there existed a strong genetic differentiation among species and a moderate genetic differentiation among populations.The result of STRUCTURE cluster analysis showed that the best K value was 3,and the three species were divided into three branches completely.However,there was still a certain degree of gene introgression between Q.chenii and Q.acutissima.The results of IBD test showed that the genetic distance and geographical distance of the three species had significant correlations(Q.variabilis: P = 0.02,R2 = 0.056;Q.acutissima: P = 0.01,R2 = 0.056;Q.chenii: P=0.05,R2 = 0.412).The analysis of historical gene flow by Migrate showed there was an asymmetric gene flow between Q.variabilis and Q.chenii.The analysis of contemporary gene flow by Bayes Ass showed that there was an asymmetric gene flow between Q.acutissima and Q.chenii.ABC analysis showed that the evolutionary model of the three species was a simple split model.The SDMs results showed that the potential distribution areas of the two widespread species(Q.variabilis and Q.acutissima)both expanded during the LIG to the LGM period,while the potential distribution areas of Q.chenii contracted.