A Study On The Population Genetics Of Partial Oedipodidae Populations In China

The locust of Oedipodidae is a large insect group of Acridoidea that can be found in various ecological habitats. The migratory locust, Locusta migratoria L. (Orthoptera: Acridoidea) and Oedaleus Fieber are two of the most important pests in many regions of the world. Locusta is a monotypic genus including nine subspecies, of which only three are found in China: L. m. manilensis (Meyen), L. m. migratoria (Linnaeus), and L. m. tibetensis. The oriental migratory locust, L. m. manilensis, is the most common subspecies occurred in east and south Asia and the Pacific Region including Thailand, Cambodia, Indonesia, Japan, and China. In China, L. m. manilensis is found in highly divergent ecologic habitats of almost all flora. The locust-breeding habitats can be divided into four types: the lakeshore locust area, the river flood locust area, the seacoast locust, and the inland plain flood area. L. m. manilensis mainly feeds on bulrush and gramineous plants. Due to its ability to consume large amount of crops and its remarkable adaptability to different adverse habitats, L. m. manilensis is regarded as a serious crop pest. The destructive outbreaks of the pest in China are increasing both in frequency and in scale, possibly due to the global climate alternations. In recent years, synthetic insecticides have often been used to control the locust in management programs. However, it has been noticed that chemical control of some locust populations has become increasingly difficult. To maintain effective control strategies, knowledge of genetic structure and gene flow between populations are required. Such information would give an insight into population genetic diversity and competence for the insecticide.Oedaleus Fieber is a common genus in Orthoptera, Acridoidea, and distributes broadly in the Asia, Europe, Oceania and Africa. In China, there are six documented species and most of the species are the dominant pests to agriculture, forestry and prairie. In many areas, Oedaleus asiaticus B.-Bienko and Oedaleus infernalis Saussure are the main dominant species in Oedaleus Fieber. Oedaleus asiaticus B.-Bienko is a harmful insect pest of gramineousplants in China. This locust is indigenous to North-prairie areas and mainly distributed in Hebei, Inner Mongolia, Shandong, Ningxia, Gansu, Shannxi, and Qinghai provinces in China. Oedaleus asiaticus B.-Bienko has extraordinary migratory capacity. It has been recorded the rapid migration of this locust into Beijing occurred in July 2002. Subsequently it was found again in Taiyuan, Shanxi province in August 2003. Oedaleus infernalis Saussure primarily feeds on gramineous plants and ranges throughout China and usually abundant in number.During the past several years, the studies of many species' population genetics have been carried out owing to the DNA molecular markers development and perfect. Microsatellite primer PCR (SSRP-PCR) analysis uses simple repeats as primers to initiate PCR amplification of genomic segments and produces a large number of markers, which can be resolved in a single gel. It can examine the variability and compare the genetic variation within and between populations. The amplified fragment length polymorphism (AFLP) is also a PCR-based technique that involves restriction of genomic DNA, followed by the ligation of adapters to the fragments generated and selective PCR amplification of a subset of these fragments. AFLP was initially applied for constructing linkage maps and it has been proven useful for the evolutionary and population genetic studies. It is a robust and reliable molecular marker assay and the number of polymorphisms detected per reaction is much higher than that revealed by restriction fragment linked polymorphisms (RFLP) or the PCR-based randomly amplified polymorphic DNA (RAPD) assay.In this study, we investigated the population-level genetic diversity of L. m. manilensis in China based on SSRP-PCR and AFLP markers. The locust materials used in this study were almost originally collected from northern" China. It expands upon our previous studies in both geographical origin of samples and different genetic markers for better understanding of genetic diversity and population structure within and among L. m. manilensis populations. This study also used the SSRP-PCR technique to investigate thelevels and patterns of genetic diversity in Oedaleus Fieber. This research is' also attempt to provide insights into the geographical origin and dispersal of Taiyuan population collecting at the gate of the Shanxi University through the analysis of their genetic similarity using SSRP-PCR technique. The research of this dissertation is summarized as follows:1. The genetic structure and genetic differentiation of ten oriental migratory locust populations were studied using SSRP-PCR technique. Three microsatellite primers generated a total number of 67 SSRP-PCR profiles for 10 migratory locust populations, of which 66 (98.5%) were polymorphic. Each primer generated a variable number of bands;multiple bands varying in size from 300 bp to 2 kb in almost all populations. The total number of scorable bands amplified from three primers ranged from 12 ((CAC)s) to 32 ((GATA) 4) among the ten populations, with an average of 22.3.As observed previously, migratory locust had a high level of polymorphism by allozyme technology. SSRP-PCR study revealed a higher level of polymorphism, proportion of polymorphic loci (P) of all populations exceeded 80% and WD population was highest. In the ten migratory locust populations, genetic diversity level estimated by Shannon Index (/) and Nei's gene diversity (H) was 0.286 and 0.171 respectively. The Nei's gene diversity (H) within these ten natural populations of Locusta migratoria L. ranged, from 0.092 to 0.144. Although the order of the populations for polymorphic loci is not the same orders for Shannon Index (I) and Nei's gene diversity (H), there is a tendency for a population that has high genetic diversity also have a higher number of polymorphic loci, but the genetic diversity of these 10 populations are not significantly different in our research.The coefficient of genetic differentiations was 0.267. This indicated the 26.7% of total genetic diversity existed among populations, while 73.3% existed within populations. Cluster analysis based on the Nei's genetic distance and Mantel test (r=0.3907) suggest that geographic distances don't have any clear effect on genetic differentiation. Analysis of molecular variance (AMOVA) corroborated the assessment of population structure. Ofthe total genetic diversity, we found that only 4.71% could be explained by the variance for different breeding habitats.2. The AFLP technique was used to investigate the levels and patterns of genetic diversity in 8 migratory locust populations in China. The four AFLP primer combinations produced a total of 232 clear fragments. The positions of AFLP bands within a readable range of 50-500 bp were considered with an average of 58 bands per primer pair. For the entire sample set, the number of polymorphic loci was variable among these populations (between 53 and 150). The largest average of the number of bands was 150 for LY population and smallest was 53 for PS population. The number of observed AFLP bands per primer pair varied between 56 and 63. Based on the proportion of polymorphic fragment (i*=98.28%), all populations exhibited similar levels of variability. There was no significant difference between these populations as determined by the percentage of polymorphic bands ranging from 98.32% to 100%. The PS population displayed the smallest number of polymorphic loci, whatever the primer combination used.Genetic differentiations by Nei's index within and among populations were 0.886 and 0.114, respectively. These results suggest that the variation of the locust was mainly contributed by 'within population' variation. To ensure this suggestion, the variance component was calculated for each group. As expected, portioning of 'within population' variation was much more than that of 'among population' for Locusta migratoria Linnaeus. Variance component analysis indicated that almost 90% of variation was caused by individuals 'within population' variation, only 9.69% was due to 'among populations' and 0.71% was contributed by 'group' variation. These results also implied the low level of population divergence among these L. m. manilensis populations.A phenetic tree showed a consensus tree to show the relationship of each individual. Basically, all individuals didn't cluster according to their geographical populations and placed within the wrong geographical populations. The AFLP based dendrogram revealed many minor groupspresented in each population. These results indicated that the divergence among these populations was incomplete, implying that genetic mixture or introgression among the populations in these subspecies. At the population level of clustering analysis, visual inspection of fingerprints placed the populations into two distinct groups. One cluster consisted of the four populations from ZM, HLD, PS, and HH;the second consisted of the four populations from YJ, LY, BDG, and PX.3. We investigated the population-level genetic diversity in eight L. m. manilensis populations in China based on contemporary use of SSRP-PCR and AFLP markers. Seven AFLP and SSRP primers produced a total of 299 bands of which 295 were polymorphic (98.7%). The proportion of polymorphic fragment was relatively high {P =95.5-98.8%), indicating that there was no significant difference between these populations and all populations exhibited a similar level of variability.Shannon Index (I) and Nei's gene diversity (H) were used as estimates of the level of polymorphism with the seven SSRP and AFLP primers among these eight populations. The gene diversity was higher within populations (Hs=0.\07) than that among populations (pst=HrHs=0.0\&), and the coefficient of gene differentiation among populations was 14.5% (average Gst). These results suggested that the variation of L. m. manilensis was mainly contributed by 'within population' variation. A total of 14.5% variability was detected among the different populations. The Nei's gene diversity (H) within the eight natural populations of L. migratoria ranged from 0.054 to 0.148. Although the order of the populations for polymorphic loci is not the same orders for Shannon Index (/) and Nei's gene diversity (H), there is a tendency for a population that has high genetic diversity to also have a higher number of polymorphic loci, but the genetic diversity of the eight populations are not significantly different from each other in our research. Therefore, there was a higher genetic variation within a population and a low level of genetic differentiation among populations. In this study, quite a level of genetic variation within a population was detected in these populations. The presentstudy demonstrated that each of the migratory locust populations had remarkable genetic variations within populations. The number of polymorphic loci (P), Nei's gene diversity (H), and Shannon index (7) based on the SSRP and AFLP markers showed a low polymorphism in the PS population, whatever the primer used, which is consistent with the data from allozyme assay. The lower genetic diversity noted in the PS populations by these three markers compared with other seven populations may stem from the result of a population bottleneck event which result in a reduction in levels of genetic variation.4. Six populations were analyzed by microsatellite primer PCP, (SSRP-PCR) technique to investigate the levels and patterns of genetic diversity in Oedaleus Fieber and to provide insights into the geographical origin of Taiyuan population. Satisfactory products of each primer yielded were chosen for analysis. A total number of 58 SSRP-PCR profiles with three primers for six populations were utilized, each primer generated a variable number of bands ranging from 8 to 18, multiple bands varying in size from 300 bp to 2 kb. For Oedaleus asiaticus B. -Bienko, twelve loci were amplified with primer 33.15 core sequences, 14 with (CAC) 5 and 18 with (GATA)4. Amplification products (CAC) 5-1200bp, 1400 bp were fixed in JQ and TY (1) populations but absent in ZH population. Other loci for (GATA) 4-700 bp, 650 bp, 600 bp, 500 bp, 400 bp, and 350 bp were used to differentiate TY population from JQ and ZH. For Oedaleus infernalis Saussure, 16 loci were amplified with primer 33.15 core sequences, 8 with (CAC) 5, and 12 with (GATA)4. SSRP-PCR study revealed a higher level of polymorphism, proportion of polymorphic loci (P) of three Oedaleus asiaticus B. -Bienko populations exceeded 80% and ZH population was highest. Compared with Oedaleus asiaticus B.-Bienko, SSRP-PCR study revealed a low level of polymorphism among three Oedaleus infernalis Saussure populations;proportion of polymorphism loci (P) was 89.7% (YMG), 88.6% (YP) and 69.4% (TY) respectively. Shannon Index (I) and Nei's gene diversity (H) used as estimate of the level of polymorphismamong three populations in Oedaleus asiaticus B. -Bienko showed a similar trend. Although the order of the populations for polymorphic loci is not the same orders for Shannon Index (I) and Nei's gene diversity (H), there is a tendency for a population that has high genetic diversity also have a higher number of polymorphic loci, but the genetic diversity of these 10 populations are not significantly different in our research. The coefficient of gene differentiation (GJf=0.188) among the three populations in Oedaleus asiaticus B.-Bienko was 0.188. This indicated that 18.8% of the total genetic diversity existed among populations while 81.2% existed within populations, which reflected the high variation within population and low genetic differentiation among populations. While for Oedaleus infernalis Saussure (G^=0.251), it appeared that the species has short-distance migratory ability, and the effects of gene exchange between populations might be insignificant.The UPGMA dendrogram showed that two populations (JQ and TY) were heterogenous as far as the genetic composition was concerned, but that a certain grouping pattern could also be traced. Population from ZH was genetically distinct from other two populations. The TY population, collected in the Shanxi University, was more similar to the geographically distant population from JQ. SSRP-PCR data (Nei's 7=0.030) and dendrogram suggested the lack of genetic divergence, implied that the two populations appear to be each other from a part of a large population.