Genetic Diversity And Structure Of Codling Moth,the Cydia Pomonella (L.)，Populations In China Inferred From Microsatellite Markers

Cydia pomonella (L.)(Lepidoptera:Tortricidae), the codling moth, is the destructive fruit pest in fruit orchard and also the notorious invasive species, spreading to nearly all the apple growing areas over71countries or regions. Host plants for codling moth include many kinds of pome fruits. As a notoriously invasive pest, the codling moth has caused a great deal of damage to production of pomes. The first reported sightings of the Chinese codling moth were in1957in Xinjiang. It has now been observed throughout Xinjiang, Hexi Corridor in Gansu Zhongwei city of Ningxia, Alxa of Inner Mongolia and southeastern Heilongjiang.The successful adaption of codling moth to different habitats and climates by forming various populations which may differ with physiological and biological traits enforces its local fitness and makes it more difficult to control. So, the understanding of the micro-evolutionary processes and the reasons caused population variation after successful invasion of codling moth in China, and also the investigation of invasive history are necessary in order to develop effective pest management and interception strategies. Furthermore, speciation primarily results from the population differentiation. For populations established over long period of time, the genetic equilibrium of drift and gene flow forms the population structuring and patterns of variation. In contrast, in newly established populations, the population genetic diversity and structure are often determined by the historical events, such as bottleneck effects (or founder effects), vicariance events and dispersal history. Studies of the micro-evolutionary of codling moth in such a newly invaded ecosystem in China has a significance for understanding the process of molecular evolution.This dissertation deals with the genetic variations of12C. pomonella populations collected from the mainly distributed regions (Xinjiang, Gansu and Heilongjiang) in China and compared them with one German and one Swiss population using eight microsatellite loci. We deeply investigates the population genetic diversity and structure of14selected population based on many parameters of genetic variation, analysis of molecular variance, Bayesian clustering analysis and phylogenetic relationship. The results and conclusions of this dissertation are as follow:1) We amplified the allelic sequences of eight microsatellite loci of339individuals from14populations, covering the potential distributions of codling moth in China. All of the eight selected loci were polymorphic and the number of alleles of each population per locus ranged from4.17to12.23, observed heterozygosity ranged from0.201to0.550.21.9%disequilibrium was found in392pairs of loci. The frequency of null alleles ranged from0.010 to0.203that is typical for lepidopteran. Four of the14populations revealed significant departures from HWE, together with high mean values of inbreeding index ranging from0.097to0.486, indicating the existence of heterozygote deficiencies.2) A west-east and north-south gradient in genetic diversity was observed based on mean allele richness and level of heterozygosity. This result can be explained by the colonization of new areas via sequential founder populations or with bottleneck effects. However, the BOTTLENECK analysis revealed no clear genetic evidence for bottleneck effect in any of the studied populations. The lack of a bottleneck effect may be determined by the recent invasion history and successful colonisation by large numbers of migrants. Moreover, the two populations from Heilongjiang showed highest genetic diversities among the studied populations, which may result from the new invasion event from different genetic resources. Taking together the higher genetic diversity and distinct genetic structure revealing by cluster analysis, we can deduce that C. pomonella of Heilongjiang were not seeded by invasion populations from western China. Furthermore, the codling moth populations from Germany and Switzerland displayed a higher level of genetic diversity compared with that of populations from northwestern China. This result supports that the codling moth in China has relatively shorter history than that in southeastern Europe, the documented origin.3) There was strong genetic structuring in14populations based on Bayesian clustering approach, AMOVA and pairwise FST. The values of pairwise FST ranged from0.040to0.337. Sixty-eight comparisons out of ninety-one showed high or very high genetic differentiations (P<0.05). AMOVA results indicated that9.64%of overall variation was explained by geographic locations which were arbitrarily grouped according to the collected regions including Xinjiang, Gansu, Heilongjiang and western Europe. Bayesian clustering analysis showed that Ili, Jinghe and Kuytun populations from northern Xinjiang had similar genetic structure (average membership coefficient, cluster red, Ili0.526, Jin0.896, Kuy0.577). The results linking to relatively higher genetic diversity estimates of the three populations suggests these three populations were established by individuals belonging to the same maternal lineage. Genetic diversity of C. pomonella population from Ili was highest among populations from northwestern China (a=9.16, Ho=0.356), suggests that Ili region is most likely to be the origin center of codling moth in northwestern China. Bayesian clustering analysis also indicated that the populations from Zhangye and Korla had similar genetic structures (average membership coefficient, cluster yellow, Kor0.760, Zha0.805), together with the results of low pairwise FST, the analysis of NJ phylogenetic tree and the records of seeding transport, suggesting that similarity of genetic structures is due to human activity associated with the movement of nursery material. The level of genetic differentiation between populations from northeastern and northwestern China was great (FST=0.157～0.324,P<0.05). The results further supports the hypothesis that the invasion of codling moth in China from at least two different path ways. In the present study, the result of Mantel test (r=0.164,P=0.176) indicated that the pattern of variation was weakly associated with geographic distance among populations from northwestern China. The weak flight capacity and the human-aided dispersal improve the differentiation of geographic populations.4) Phylogenetic analysis based on NJ tree indicated that the Jinghe, Ili and Kuytun populations form northern Xinjiang had a close phylogenetic relationship. This result is consistent with the result of Bayesian clustering analysis. The close phylogenetic relationship between populations from Zhangye and Korla further confirms the probability of human-aided dispersal over large geographic distance. We also found the populations from Heilongjiang had similar genetic structure with those of western European populations. A phylogenetic study based on a greater number of collection sites is necessary to clarify the relationship between C. pomonella populations from Eropean countries before precise conclusions can be drawn, especially the phylogenetic relationship of populations from western Europe and far east region of Russia, the latter is close to Heilongjiang and was documented as distributed region of codling moth. The neighbor joining tree did not show distinct phylogenetic relationship associated with geographic distribution, which can be explained by relatively short history or passive dispersal by anthropic factors.