Studies On Population Genetic Structure Of Houpo?a Officinalis

Genetic variation of a species is a product of long-term evolution and can reflects some special events in evolutionary history.So the studies of genetic diversity and genetic structure are the basis of biological adaptation and species formation and the core content of conservation biology.Spatial genetic structure(SGS)plays key roles in the short-term evolution.Therefore,studies on SGS may help us to know the population dynamics,as well as to develop effective strategies for conservation of endangered species.Houpo?a officinalis(Rehder&E.H.Wilson)N.H.Xia&C.Y.Wu.comb.Nov.is an endangered medical plant in China.It had a relatively wide distribution throughout South China.Because of its high medical value,H.officinalis populations have been severely destroyed and most subpopulations have become locally extinct in recent decades.As a result,H.officinalis has been categorised as CITES category 2,a species at risk in China.Twelve EST-SSR marks developed from transcriptome data were used to analyse the genetic diversity and genetic structure of 336 individuals come from 14 natural H.officinalis populations.Meanwhile,age class,distribution pattern,spatial genetic structure and gene flow of Zhejiang Suichang population were also analyzed.On this basis,endangered mechanism and protection strategy were as below:Natural distribution and current H.officinalis situation of population:According to specimen recordsfrom,the H.officinalis population is mainly distributed from 22 38?N to34 59?N,and from 98°31?E to 121°18?E.Filed investigations have indicated that the distribution area of H.officinalis has been increasingly reduced.With the community degradation and vegetation degeneration,the regeneration of the population was poor.Characteristics analysis of H.officinalis transcription and development of EST-SSR markers Illumina-Solexa Genome sequencing platform was used and the sequences were assembled.All together 109526 unigenes with an average length of 1023bp were acquired.There were 60361,39942,65535,51351 and 27310 unigenes been annotated through BLASTX against the NCBI Nr,Swiss-Prot,GO,KEGG and KOG database.A total of 25949 sequences with 27721 SSRs through transcription of H officinalis were detected,SSR sites occurred with an occurrence frequency of 23.67%.Among the total of 374 identified EST-SSRs,CT/GA and AG/TC were the dominant di-nucleotide repeat motifs,AGA/TCT and AAG/TTC were the dominant tri-nucleotide repeat motifs.A total of 180 SSR markers were randomly selected for validation,of these,104 produced reproducible amplicons and 21 were polymorphic among 14H.officinalis genotypes from diverse geographical locations in south China.Genetic diversity and population genetic structure of H.officinalis Twelve expressed sequence tag SSR(EST-SSR)markers were chosen to analyze the genetic diversity and structure of fourteen natural populations.The results indicated that moderate genetic diversity,high genetic differentiation and relative low gene flow existed in this plant(He=0.600,Fst=0.327,Nm=0.515).STRUCTURE and UPGMA analyses showed that H.officinalis populations could be divided into 3 different groups,and the west group had higher genetic diversity than the central and east groups.The historical migration rates among the groups were low and unsymmetrical,and there was no significant correlation between Nei's genetic distance and geographic distance(r=0.052,p=0.330).According to BOTTLENECK analyses,most population except YNTC?GZLP?ZJSC population did not suffer bottleneck effect,indicating negative effects of habitat fragment haven't shown out yet.Population dynamics of H.officinalis of Zhejiang Suichang population Suichang H.officinalis population was belonging to the decline populations.Static life-table and survival curves indicated that there were two stages with high mortality,the seedling stage and the juvenile.Time series prediction showed that a lack of seeding and an increase in old individuals will aggravate the declining state of the population.If there is no improvement in seeding number,the population will soon decline to almost the extinct position.The populations conformed to a poisson distribution on a small scale(25~50 m~2)and an aggregated distribution on a large scale.The suitable habitat will delay the trend of declining and make the population long-term stability development.Spatial genetic structure of Zhejiang Suichang population The genetic diversity of the Suichang population of H.officinalis was relatively high(He=0.78)and there were no significant differences among the different age classes(P>0.05).However,most locus deviated significantly from Hardy-weinberg equilibrium,Ho was lower than He with a Fixing index of0.685,and a high selfing rate existed for all age classes(Fis=0.81~0.86),which indicated an obvious deficiency in heterozygosity.All individuals in the population had significantly positive SGS with a space length less than 100 m,and significant negative SGS with a space length between 300 and 450m,while no SGS was observed other spaces.This means that patch patterns have emerged in this species.GeneAlEx and Cerves analyses showed that the seed flow of H.officinalis were 2.7~627.4 m,the pollen flow was 0~171.7 m and the gene flow was 3.91~639.04 m.The results show that habitat fragments have caused a decline in inbreeding and obviously infected SGS and the gene flow of the species.Endangerment mechanism and protection strategy of H officinalis Based on the study described above,we analysed the endangerment mechanism through breeding systems,fertility characteristics,regeneration disorders,genetic diversity,population characteristics,spatial genetic structures and the gene flow of the species and developed a corresponding protection strategy.In this protection strategy,cutting adult trees and digging seeds must be forbidden to maintain effective population size.Additionally,suitable habitats should be protected to prevent further deterioration.This strategy will create suitable living conditions for seed germination and seeding development to promote the regeneration of the population.The species has differentiated into western,central and eastern groups.They should be protected as independent ESUs.Transplants should be carried out in different populations to enhance population genetic diversity,and manual methods should be carried out to promote gene communication among different populations.These methods should be carried out in“Genetically homogeneous regions”.Pollinated insects showed be protected to enhance pollen flow,and seed dispersing birds should be protected to enhance seed flow.