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Population Genetic Structure Of Oxya Chinensis From Northern China And The Relationship Among Allozyme Genotypes And Malathion Acute Toxicity

Posted on:2005-12-23Degree:MasterType:Thesis
Country:ChinaCandidate:F P LuFull Text:PDF
GTID:2133360122488626Subject:Zoology
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The massive outbreaks of Oxya chinensis had become increasingly serious in recently years along with the changes of the agricultural practices, ecological environments and the global climatic conditions. It is commonly believed that insect populations have different characters as a result of adaptation to each geographic ecological and environment, implying that the population control may vary depending on the target population genetic structure. Such knowledge can provide useful information for the insect swarming prevention and overall pest management. Previous studies have related differential malathion acute lethal effects on allozyme genotypes of Oxya chinensis, suggesting that the allozyme genotypes may be a potential indicator to evaluate resistance of Oxya chinensis to malathion toxicity. The terrestrial grasshopper of Oxya chinensis heavily depends on water in its habitats. A moderate geographical barrier might significantly restrict the gene exchange among populations, which may result in the accumulation of local genetic diversity within population and the development of genetic divergence among various populations. The existence of the population genetic differentiation implies that the monitoring of resistance to pesticides are needed thorough such differences and the control practices are dependent on local conditions with the consideration of population's genetic background.This thesis studied the genetic structure of three populations of Oxya chinensis from Shanxi and Shaanxi province and estimated the level of genetic divergence. The LC50 values of the samples from each population were then measured. 276 to 533 individuals of Oxya chinensis in each population were injected with malathion at a concentration of corresponding LC50 values. The survivor and the dead individuals were then assayed using allozyme analysis to individually examine the genotypes. Five polymorphic loci were selected as molecule genetic marker to explore the possible correlation between allozyme genotypes and malathion lethal effects. When the significant allozyme effects on the moralities were observed, the pairs of individuals of each genotype were either defined as the resistance or sensitive genotypes according to the mortality difference. Therefore, the genotype may be useful as a marker to survey the population resistance level.The allozyme analysis of thirteen loci (Adk, Ck, -Gpdh, Hex-1, Hex-2, Idh-1, Idh-2, Ldh, Me, Mdh-1, Mdh-2, Pgi and Pgm) demonstrated that the genetic variation within a population and among all the three populations. Loci of Ck, Idh-1 and Mdh-2 were found monmorphic in all three populations whereas more than one alleles were observed at the rest loci. A clinal tendency in allele frequency was observed at the locus of Ldh. From north to south the frequency of Ldh-a was 0.631 in YM population (Yangmingbu, Dai county, Shanxi), 0.720 in JY population (Jinyuan district, Taiyuan, Shanxi), and 0.852 in YQ population (Yangqiao, Chang'an County, Shaanxi) The three Oxya chinensis populations showed relatively high percentage of polymorphic loci (53.8% to 61.5%), the mean number of alleles per locus (A=2.1~2.7) and observed heterozygosity (Ho=0.176-0.181). The genotype frequency at most loci significantly deviated from Hardy-Weinberg expectations except for Ldh and Pgi in all the three populations. Me and Pgmwere significantly deviated from Hardy-Weinberg equilibrium in all the three populations. Although Fst in nine loci were significantly deviated from Hardy-Weinberg equilibrium, the overall Fst was not deviated from Hardy-Weinberg equilibrium (overall Fst=0.037, P>0.05). Nei's genetic identity were high (0.990 to 0.996) and showing the less divergence level among the three populations inspite of the obvious geographic isolations. In cluster analysis based on Roger's genetic distance, the geographically closer populations of YM and JY grouped first and then grouped with YQ population. This may imply that the genetic distance was positively correlated with geographic distance. However more pop...
Keywords/Search Tags:Oxya chinensis, Population genetic structure, Differentiation, Malathion acute toxicity, Selective lethal effect, Allozyme genotype
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