Microsatellites Isolation And Population Genetic Structure Analysis Of Sogatella Furcifera And Laodelphax Striatellus In China

The white-backed planthopper (WBPH),Sogatella furcifera (Horvath) and the small brown planthopper (SBPH), Laodelphax striatellus (Fallen), which belong to Hemiptera, Delphacidae, are two serious rice pests in China. The white-backed planthopper was considered as an insect with long-distance dispersal ability. However, the exact primary source and migration routines are still in debate. Meanwhile, the molecular methods involved in the study of the SBPH had been done scarcely. Therefore, it is highly necessary to develop efficient molecular markers to investigate the possible routes, the population structure and the dynamics during these two pests migrate. Currently, microsatellites and mitochondrial DNA are the most popular markers for ecological applications since they provide more accurate information about dispersal, population diversity, and population structure, and so on so forth. Therefore, in this paper, we developed a series of SSRs for both insects. With the help of the newly developed SSRs and a fragment of mtDNA, we did a preliminary research on the population genetics of WBPH and SBPH separately.In the study based on microsatellite markers, we developed some new microsatellite markers for WBPH and for SBPH. We also demonstrate the utility of the new markers by conducting a preliminary population structure study on five WBPH geographic populations and three SBPH populations. The high polymorphism and ease of use of these loci suggest they will be powerful tools for population genetic and dispersal studies in the future. The main results are as follows:(1) We first downloaded the WBPH and SBPH transcriptome data from the NCBI Short Read Archive database. By splicing and further processing of the transcriptome data, PCR primers were designed and validated, and ultimately we developed 19 polymorphic microsatellites of the white-backed planthopper and 7 new SSRs for the small brown planthopper. These microsatellites markers can be used for population genetic sturcture and genetic diversity reseach.(2) According to the 19 microsatellite loci which we have been developed. And with the help of Multiplex Manager 1.0 software, we then screened 19 microsatellite loci, fluorescently labeled multiplex PCR system and optimized the reaction conditions, and finally put the 19 microsatellites into four different sets of multiplex PCR combination. Within each set, it contains 4-7 SSR. The genotyping efficiency had been greatly improved when the combination of multiplex PCR microsatellite loci is involved.(3) The results of the microsatellites implied that the five WBPH populations had moderate levels of genetic diversity and low levels of population differentiation. The results of each locus alleles with 3 to 14, average 6.8 were detected. In total, we found 156 alleles. The observed and expected heterozygosities range from 0.105 to 0.766 and 0.099 to 0.783 respectively. Population genetic structure analyses revealed that the 5 WBPH populations had a low level of population differentiation. Pairwise estimates of FST calculated between pairs of populations were very low, ranging from-0.0015 to 0.0073, with an average FST of 0.003. This indicated that long-distance migration of this pest allowed genetic mixing between populations from remote geographical origins. In future, these new microsatellite markers will be powerful tools for population genetics studies of S. furcifera.In the study of mtDNA involved SBPH population analysis, we studied the population structure of 26 L. striatellus populations in China based on a COII gene fragment. We conclude these results:(1) 1144 individuals from 26 Chinese populations were amplified and sequenced for a fragment of mitochondrial gene COII. The 650bp fragment length amplified from COII sequence had 42 variable sites,13 of which were parsimony information sites, and 27 were singleton sites. It indicated no insertion or deletion found in all sequences. The A+T contents were considerably higher than G+C contents. The overall haplotype diversity and nucleotide diversity of COII gene were 0.596 and 0.132% respectively. Analysis of haplotypes composition displayed 46 haplotypes in COII gene,11 of which were shared among populations, and the other 35 were private haplotypes.(2) The results of AMOVA suggest the population divergence mainly exist within groups. Pairwise estimates of FST are non-significant between most populations which indicate the difference between populations is very low. But there is a case worth noticing: the populations group form the northeast of China had more significant FST with other populations in the study, the value of FsT ranged from 0.1 to 0.4, indicating these populations had genetic difference to other populations. The results of neutrality tests found the value of Tajima's D was negative and significant when all the populations were considered as one group and the Fu and Li's D test showed the same pattern. Meanwhile, the mismatch distribution were unimodal which indicates a recent population expansion may occurred in all populations.