Study On Genetic Structure Of Laodelphax Striatellus Populations Based On DdRAD-Seq Technology

The small brown planthopper(SBPH),Laodelphax striatellus(Fallen)which belongs to Hemiptera,Delphacidae,is an important rice pest and distributed in the world.Due to its ability to ovcrwinter through diapause,SBPH is generally considered to have no long-distance migration habit.However,in recent years,more and more evidences show that SBPH has the habit of long-distance migration,but the migration route is still unclear.In this study,ddRAD technology was used to construct a simplified genome library of SBPH,and compare the ability that genome-level SNP and microsatellite markers reveal the genetic structure of SBPH;the relationship between Chinese and Japanese population was studied by SNP.The following results are obtained.1)We successfully constructed the library for four geographic populations of SBPH using ddRAD method.The bases of these libraries are evenly distributed,the average Q20 and Q30 of all reads obtained by sequencing were 97.3%and 93.4%,indicating that the library constructed was of good quality.A total of 5,535 SNPs was obtained under the condition that the minimum sequencing depth was 10 and 80%of individuals in each population had these sites.After the SNPs were filtered,583 SNPs were retained with the conditions of a minimum allele frequency(MAF)>=0.05 and r2<=0.2.2)The results of population genetic structure research show that DAPC analysis based on SNP data can clearly distinguish SBPH from the four geographic populations,while the ability of microsatellite data to distinguish different populations is low,indicating that SNP markers are indeed more advantageous than microsatellite markers in revealing the population genetic structure with low genetic differentiation level.We then studied nine populations in China and six populations in Japan using the ddRAD method,and found the mainly significant differentiation between populations in two countries and Japan.The two coastal populations of Japan were not significantly differentiated from the populations in Jiangsu province(Lianyungang,Yancheng)and Shandong province(Jining),and these populations had close relation,which provides molecular evidence for that SBPH can migrate from mainland in China across the ocean to Japan.The results are as follows:1)The observed heterozygosity(HO)was between 0.5248 and 0.5823 in China and Japan populations,and the nucleotide diversity(π)was between 0.3337 and 0.362,which indicate that the genetic diversity of all groups of SBPH is no obvious difference.2)The most geographic populations of SBPH in Japan were significantly differentiated from those in China,but there was no significant differentiation between the two coastal populations of Japan near China and populations from Jiangsu province and Shandong province in China.Except for the northernmost population from Yanshou prefecture,the differentiation among the other populations was not significant in China.And except that Hokkaido and Saitama populations,Kagoshima and Shimane,Niigata and Saitama populations were not significantly differentiated,other populations were significantly differentiated in Japan.3)DAPC clustering results show that different individuals can cluster together according to the sampling site.The results of bayesian clustering show that these populations can be roughly divided into Chinese population and Japanese population,and there are mixed models between these two populations,suggesting that there is gene exchange between the SBPH populations in China and Japan.However,because of the strong gene exchange between the populations,STRUCTURE could not reveal the specific genetic structure between geographical populations.