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Population genetics of Aedes albopictus (Diptera; Culicidae): molecular markers in the nuclear host and Wolbachia genomes


Aedes albopictus is a Asia native mosquito, it was identified in Brazil in 1986. This species is the primary vector of dengue fever (DF) in Asia. Studies have not showed an association of these mosquitoes with transmission of DF in Brazil, despite the laboratory studies have shown that Ae. albopictus is competent to transmit the serotypes of DF viruses. Due to incompatibility and the potential competence, this species is of great concern to human health as a marker to inferences about natural infection of arboviruses. Some investigators examined the levels of genetic variation in field populations of Ae. albopictus, as well as the genetic structure of this populations. Knowledge of the genetic structure of the vector populations is required to maintain effective vector control strategies. Analyses of allozymic patterns in Ae. albopictus populations have revealed relatively high levels of genetic variation. However, studies have showed absence of variation in mitochondrial sequences among the populations. An hypothesis to explain the contrasting levels of nuclear and mitochondrial diversity has been related the infection Ae. albopictus by Wolbachia. Wolbachia are endosymbionts of arthropods, especially insects. The only survey of genetic variation using allozymes in Ae. albopictus from Brazil was conducted among closely located populations. Three samples were collected between 1987/88, few years ago of introduction into Brazil. Actually, this mosquito is found in another 17 brazilian states, it has been reported in urban and rural localities. Ae. albopictus seems to be competing with Ae. aegypti in some parts of the city. Our experiments have indicated the absence of variation in mitochondrial DNA of Ae. albopictus when contrasted with Ae. aegypti. Thus, due to these results, the purpose this study is to estimate the variability of natural populations of these mosquitoes. Such comparative analysis of genetic structure of closely related populations will be studied using protein polymorphisms and the diversity of Wolbachia infection in mosquito. Therefore, the results expected in the present study may reflect the new dispersal of populations: the distribution of the polymorphism and alleles distinctly fixed in these populations may be significantly different. We have recently sampled populations of Ae. albopictus from the natural habitats. Some samples were collected within the urban perimeter of Mogi das Cruzes City (SP). Assays for Wolbachia infection were performed by PCR amplification of the 16S rDNA gene, utilizing the 16S specific primers for Wolbachia gene. We found that all females, eggs and larvae sampled from sites were infected with Wolbachia. Wolbachia can be typed into different groups or strains. We have used PCR amplification of the wsp gene for the two Wolbachia strain wAlbA and wAlbB known to occur in Ae. albopictus. The wsp gene is the most variable Wolbachia gene characterized to date. Our results have identified populations infected with only a single strain of Wolbachia (wAlbA). Other primers are available that can be used to distinguish strains and variants of endosymbionts. Wolbachia infections in Ae. albopictus cause a reproductive effect known as cytoplasmatic incompatibility, which results in reproductive isolation with uninfected and infected or between different strains. Thus, the Wolbachia infection through the host populations can be used as a molecular marker to study inferences about gene flow, effective population size, the geographic origin of invasive population and the number of invasion events by Ae. albopictus. This kind of information has important implications for the success of programs to control mosquitoes populations. The ability of Wolbachia to spread through populations has generated an applied interest in using the symbiont as a mechanism to drive introduced transgenic traits into vector populations to control mosquito-borne diseases. (AU)

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