Inference On The Origin, Colonization Routes And Dispersal Patterns Of The Oriental Friut Fly, Bactrocera Dorsalis(Hendel), Based On Molecular Markers

The oriental fruit fly, Bactrocera dorsalis (Diptera:Tephritidae), being highly polyphagous, seriously threats the production of fruit and vegetable. It is useful for revealing the factors contributed to successful invasion and designing control strategies to reconstruction the invasion history of the B.dorsalis. However, researches concerning the invasion history of the B.dorsalis are limited because of the lack of sampling locations and the simplex analysis methods. Hence, following four researches were carried out:1. infered the origin region and invasion routes of the B.dorsalis used coxl of mtDNA,2. analyzed the dispersal patterns of the B.dorsalis in China Mainland jointly used nadl, nad5and cytb genes,3. revealed the genetic structure of the B.dorsalis populations invading in Chongqing, China in recent years,4. researched the influence on the genetic structure of the B.dorsalis populations after host transformed. Following are the results and conclusions.1. Inferred the origin region and invasion routes of the B.dorsalis. A total of552oriental fruit flies from35populations were used in the analysis, including256B.dorsalis adults collected from14locations in China and one in Pakistan. Information from these locations was completed with296additional sequences obtained from GenBank that together cover20locations in eight countries and constitute a reasonably complete coverage of the distributional range of the species.A total of125polymorphic sites were found in the505bp coxl sequences,83of those sites were parsimony-informative. A total of217unique haplotypes were identified, just47of those were shared haplotypes. Eight haplotypes of Taiwan population were shared by18populations of Inland China, Southeast China and Southeast Asia. Almost no shared haplotypes were found between populations of Southeast China and Southeast Asia beside the haplotypes shared with Taiwan populations. Populations of Inland China shared haplotypes with populations of Southeast China and Southeast Asia contemporarily. The Honolulu population of Hawaii, USA did not shared any haplotypes with Asia populations and the Lahore population of Pakistan just shared one haplotypes with Panzhihua population. The genetic diversities of the two populations were low, while high genetic diversities were observed in other33populations. The genetic diversities of the populations established recently were high than populations established for a long time. The marginal populations like Lahore and Honolulu were genetic difference from other33populations significantly. Based the locations of the35populations and previous researches, seven populations were defined. The FST values between two population groups increased along with the increase of the geographic distances. The demographic history of the7population groups indicated that Taiwan group had experienced population expansion, and had the longed expansion time. The increased trend of the expansion time from Taiwan west-ward was also observed. The N.J phylogenetic tree of the35B.dorsalis population showed two main clades, and populations from Southeast China and Southeast Asia were belong to the two claeds respectively, while populations from Inland China distributed on the two clades randomly. The situation that two population groups of Asia and Hawaii defined by SAMOVA indicated that the Pacific Ocean might be the main barrier of gene flow between populations in Asia and Hawaii. AMOVA results showed that29.28%of genetic variance occurred between the two population groups. MJ networks of haplotypes showed that almost all of the haploptypes of Hawaii group clustered together except haplotype of H208. Estimation of asymmetric migration rates between pairwise populations found limited gene flows between populations of Hawaii and others.Based on the history records and genetic data, Taiwan Island was inferred as the origin region of the B.dorsalis. After originated from Taiwan, the B.dorsalis might colonize along two main routes. One was Taiwan to Southeast China and another was Taiwan to Southeast Asia. The fronts of the two routes might be coinciding in Inland China. The resource of the B.dorsalis in Pakistan was puzzle. While, the B.dorsalis in Hawaii might be introduced in by human after the Second World War. High genetic differentiation between Hawaii population and Asia populations may due to the isolation by the Pacific Ocean and the strict quarantine measures implemented in Hawaii. Based on the genetic data, control strategies were proposed.2. Dispersal patterns of the B.dorsalis in Mainland China. The polymorphic sites of nadl, nad5and cytb were101,129and186, respectively. Collapsing of individual sequences led to the identification of132,142and143unique haplotypes for genes nadl, nad5and cytb, respectively. The haplotypes constitution of the12populations showed that the proportions of shared haplotypes were relatively high in Fuzhou and Guanzhou populations, while populations established recently were mainly constituted by rare haplotypes. Genetic diversities were high for each population based on concatenated sequences as well as each of the three genes independently. Furthermore, genetic diversities of populations recently established were higher than populations established for several decades. Not significant genetic differentiations were observed between populations of Southeast China and Inland China. Mantel tests suggested that the genetic differentiation between populations was not caused by geographic isolation. Three population groups of the12populations were defined by SAMOVA, however, no significant genetic differentiations were found among the three groups. AMOVA results showed that only10%genetic variances were among different groups. Traditional haplotype phylogenetic trees plus MJ networks for each gene indicated weak genetic structures. Most migration rates between pairwise populations were symmetric, asymmetric migration rates were observed between Gangzhou population to Fuzhou, Wenchang, Wuhan, Jiangjin, Xiushan and Wanzhou. Significant or highly significant values of Tajiama's D and Fu's Fs, contemporarily with unimodal mismatch distribution suggested that the B.dorsalis in China had experienced significant population expansion, and the expansion mainly occurred in Inland China. Ratios of effective population size between before and after expansion indicated big population growth.Based on the genetic data, we inferred that:1. the B.dorsalis experienced significant population expansion accompanied with big population growth in Inland China,2. multiple invasions of the B.dorsalis counteracted the bottleneck effect in population establishment stage,3. the Southeast China might be the bridgehead of the B. dorsalis colonized in inland.3. The genetic structure of the B.dorsalis in Chongqing region. The researches were implemented using eight highly polymorphic SSR sites. A total of51alleles were found in the6B.dorsalis populations from Chongqing. MS4site had the most alleles, whereas3.2B site had few alleles. Shannon's and Nei's index suggested that the genetic diversities of the6populations were high. Test of bottleneck effect using I.A.M and T.P.M hypothesis models did not show recent bottleneck of the6B.dorsalis populations. Low observed heterozygosity of the6population lead deviation of Hardy-weinberg equilibrium on most SSR sites. Estimations of fixed index showed high intra-population inbreeding coefficient and total inbreeding coefficient indicated, and low genetic differentiation coefficient. High level gene flows and low genetic distance among populations also reflected the low level genetic differentiation. Two clades of the6populations were clustered by Structure. The results showed that the constitution of individuals of Wulong population was somehow different from other five populations. NJ population trees demonstrated the results above.We could infer that:1. the B.dorsalis might colonize in Chongqing along two different routes,2. multiple invasions leaded the high population genetic diversities and overcame the bottleneck effect in population establishment stage,3. the intra-population inbreeding resulted from limited population size might lead heterozygosity lack and deviation from Hardy-Weinberg equilibrium.4. Influence of the host transform on population genetic differentiation. The researched populations were obtained through transformed partial B.dorsalis individuals subcultured with banana to navel orange, then subcultured with the two host fruit. Four pairs of SSR primers with relatively high polymorphic on laboratory strain were used. All of the6laboratory populations (JF5, CF5, JF10, CF10, JF15, CF15) showed low genetic diversities, furthermore, the genetic diversities of the navel orange populations declined along with increase of generations. Hardy-Weinberg equilibrium changed from deviation to equilibrium along with increase of generations of the two host populations. Very limited gene flows were found among the6populations. The Nei's standard genetic distances between two host populations of same generations were low at first, then, increased with cultured generations. Genetic distances between banana and navel orange populations of same generations were lower than that between different generations of banana or orange populations. AMOVA results based on generation groups and host groups, respectively, also demonstrated that genetic variance among generations was bigger than that between two host populations.Above results might be due to:1. isolation and selection mainly contributed to low genetic diversities of the laboratory populations and to genetic differentiation between two host populations,2. more intense effect of genetic drift than selection leaded bigger genetic differentiation among generations than that between two host populations,3. population size growth and adaption to host saved the populations from Hardy-Weinberg equilibrium deviation.