Fine-Scale Spatial Genetic Structure Of An Endangered Plant Sinomanglietia Glauca (Magnoliaceae)

The studies of plant fine-scale spatial genetic structure(FSGS)can directly quantify the genetic relationships among individuals in populations,reveal the gene exchange patterns within and among populations,and provide an important reference for the protection of endangered plants.In this study,population genetic analysis was performed on two populations of Sinomanglietia glauca Z.X.Yu & Q.Y.Zheng in Yunpan Village of Yongshun County of Hunan Province(HN)and Yujing Mountain of Yichun City of Jiangxi Province(JX)using 21 polymorphic simple sequence repeat(SSR)loci.Furthermore,FSGS of the two populations and different patches of JX was further analyzed.According to its genetic background and survival status,this paper explored the factors that contribute to the endangered species and put forward feasible scientific suggestions for its conservation and management.The main results of this study are as follows:In this study,2184 SSR loci were detected from the reduced genomic sequence of S.glauca by genotyping-by-sequencing(GBS)using second-generation sequencing technology,among which tri-nucleotide and di-nucleotide repeats were dominant.The SSR markers developed by this method were found to be highly informative and polymorphic.Then,21 pairs of polymorphic SSR primers were selected for population genetic analysis in HN and JX populations.By genotyping 568 individuals(HN,N = 94;JX,N = 474)using the screened 21 SSR markers,this study found that the average genetic diversity of S.glauca was low(Shannon’s information Index,I = 0.66 and observed heterozygosity,He = 0.34).The genetic diversity of HN population(I = 0.12,He = 0.08)was much lower than that of JX population(I = 1.19,He = 0.61),which means that most of the genetic diversity of S.glauca was contributed by JX population.There were also significant differences in genetic diversity between patches and age classes in JX populations.Genetic differentiation of the two populations was high(Fst = 0.436).PCA,UPGMA phylogenetic reconstruction and STRUCTURE all showed that the two populations were genetically distinct.There was also genetic differentiation among the seven patches of the JX population.Limited gene flow(Nm = 0.323)was the main reason for the strong genetic differentiation among populations,while strong genetic drift may have occurred within populations.The results showed that there were heterozygote deficiencies in both populations,but much more serious in HN population(F = 0.162)than in JX(F = 0.017).Molecular genetic estimator(θ)was much higher in JX(θ = 11.623)than in HN(θ =1.003),which indicated that the effective population sizes of JX was much larger than that of HN.There was asymmetric historical gene flow between the two populations.The migration rate of historical gene flow from JX to HN was very strong(M = 0.185),and that from HN to JX was weak(M = 0.058).However,the migration rate of modern gene flow(m)was small between the two populations in both directions.Restricted contemporary gene flow could be the cause for high genetic differentiation in S.glauca.This study found significant fine-scale SGS in both populations,but much stronger in HN(Sp = 0.477)than in JX(Sp = 0.0617).Fin-scale SGS was also observed in different patches of JX population,except region A,and in both age classes of JX population.In particular,region G had a high fine-scale SGS(Sp = 0.8101).Compared with adult trees(Sp = 0.0594,40 m),saplings had higher SGS(Sp = 0.0878)and larger distance(120 m).The limited gene flow was the main reason for the formation of SGS in the natural population of S.glauca.Habitat fragmentation,competitions of other plant species in the same community and microhabitat all contributed the spatial genetic structure of S.glauca population.In summary,we verified the existence of more significant fine-scale spatial genetic structure in both HN and JX populations in S.glauca from multiple aspects of genetic diversity,genetic differentiation,gene flow and fine-scale spatial genetic structure.Through quantitative comparison,SGS intensity in HN population was much higher than that in JX population.Different levels of but significant SGS were found in the JX population patches and age classes.Limited gene flow was the main reason for SGS formation in the population.Differences in species biological characteristics and small-scale habitat resulted in different SGS in subpopulations.