Diversity Of The Endosymbiont Wolbachia In Thysanoptera And Its Affection On Host Mitochondrial COI Gene

Thysanoptera is generally called Thrips. There have been 7400 species on record as yet. In China there are 336 species on record, in which some species are invasive species. Some thrips are serious pests in agriculture, especially in green house. Endosymbiotic bacteria of the genus Wolbachia infect a lot of arthropod and nematode extensively. The classification of the genus Wolbachia is not definite. Presently, the Wolbachia is classified into eight (A-K)"supergroup". Wolbachia could manipulate host's reproduction by Cytoplasmic Incompatibility (CI), Arthenogenesis Induction (PI), Male Killing (MK), Feminization and new species forming by reproductive isolation.Both mtDNA and Wolbachia are in cytoplasm. Wolbachia is a kind of intracellular bacterium, and it is matrilinear inheritance as mtDNA. In cytoplasm, mtDNA and Wolbachia may be correlated in a long time. In many Wolbachia infected hosts, mtDNA's diversity has changed, althongh not with the same pattern. Accordingly, we presume that thrips'parthenogenesis is related to Wolbachia infection and Wolbachia may affect thrips'mtDNA.In this thesis, 496 individuals from 50 thrips species (representing 2 suborders, 3 families) were studied by molecular method. COI is selected used as a molecular marker for molecular identification, gatB, coxA, hcpA, ftsZ, fbpA and wsp are used to detect the infection of Wolbachia and for the Wolbachia classification. The effection of Wolbachia infection on the diversity of mitochondrial COI diversity was analyzed. The main results are as following:(1) We compared molecular and morphological methods on the identification of 50 thrips species in 496 individuals. The results showed that these two methods are consistent in most species except for four species in two pairs, i.e. Odontothrips loti and Odontothrips meliloti, Thrips physapus and Thrips pelikani. The genetic distance between each pair is 0.1% and 0.3% respectively. Then the nuclear marker ITS2 is used for further analysis. We found that the ITS2 sequences of O. loti and O. meliloti are identical completely. Furthermore, the 6 genes in Wolbachia of the two species are almost the same.(2) In all the 50 species, 25 thrips species are infected by Wolbachia with infection ratio from 6% to 100%, in which two species are multiple infection. Suborder Terebrantia has higher infection ratio than suborder Terebrantia. The infection is related with what thrips feed. The three species, showing predacity at least in some developmenatal stages, are all infected and the infection frequency is higher than others. The infection statuses in different populations also show discrepancy.(3) Totally, 135 coxA,134 gatB,135 ftsZ,135 fbpA,133 hcpA sequences and 135 wsp were sequenced from 135 thrips specimens. Three kinds of sequences were used to analyze Wolbachia supergroups: only wsp, only ftsZ and concatenated gatB, coxA, hcpA, ftsZ and fbpA genes. The wsp gene sugguests most Wolbachia belong to supergroup A and B, except 2 sequenses are similar with supergrorup G, but not belong to any supergroup. The ftsZ and concatenated genes indicate that all the infected Wolbachia in thrips belong to supergroup A and B. Our results showed that the taxonomy system of Wolbachia should construct anew.(4) The analysis showed that there is frequent recombination in wsp but no recombination in coxA, fbpA, gatB, hcpA, ftsZ. With 2 special seqences, we presume G supergroup really is the recombination result of suopergroup A and B. This result raises doubt to the usage of wsp for Wolbachia classification. Wolbachia classification system requires further researches in choosing the appropriate gene markers. We also found predatory thrips has higher recombination ratio than other thrips. We presume the Wolbachia recombination status may be related with the food containing Wolbachia. So these are valuable resource for studying Wolbachia and its interactions with host.(5)COI sequense analysis indicated that Wolbachia may influence the host's mtDNA. We test the mtDNA nucleotide diversity and genetic distance. The relation is that the infected groups of thrips has fewer COI haplotypes than uninfected one; in the same genus, the average value of genetic distance between infected species is smaller than that in uninfected thrips species. The average genetic distance between infected and uninfected species is bigger than both within infected and uninfected species. All the results support the known presume that Wolbachia makes its host's mtDNA diversity decrease. The experiment result is very helpful for research in evolution of thrips and Wolbachia. On the one hand Wolbachia decreases the host's evolution to make its existence steadily,on the other hand makes the host depart the neutral evolution.Our research suggests the morphological and molecular identification are needed in precise species taxonomy, which affords keys and evidence for many research aspects. The relation between Wolbachia infection and host'biological characters and the special characters of wsp make Wolbachia research more comprehensive. The affection of Wolbachia on host'mtDNA is valuable for exploring how Wolbachia realizes its manipulation to host. Wolbachia taxonomy and evolution is complex, but it deserves our further researches.