Variabilidade genética em populações de Aedes aegypti (Díptera: Culicidae) da Região Meio Norte do Brasil

Abstract

The Aedes aegypti mosquito is a vector of great epidemiological importance for it transmits viruses which cause the yellow fever, dengue and the chikungunya fever. This study analyzed the genetic variability and the population dynamics of Ae. aegypti at the mid-northern region of Brazil using mitochondrial (NADH4) and nuclear (microsatellites) DNA sequences. Samples of larvae and pupae were collected in four states of the mid-northern region (Pará, Piauí, Maranhão and Tocantins), and sampling was accompanied by an endemism agent. Traps to collect eggs were placed at the vicinity of the visited houses, where they were left for five days. The collected material was transported to the laboratory Genética e Biologia Molecular of the Centro de Estudos Superiores de Caxias CESC/UEMA, where laboratory procedures for DNA extraction and PCR were performed. The NADH4 genes were sequenced using 119 specimens of 11 populations from the state of Maranhão. One fragment of 337 bp, nine haplotypes, 12 informative sites, h= 0.673 and π= 0.01628, were obtained. The AMOVA indicated that the largest variation occurred within populations (67.46% - FST = 0.325), with significant P (<0.001). The paired FST values indicated that the gene flow between populations is restricted. The phylogenetic analyzes grouped the haplotypes found in this study with the haplotypes found in other studies from Brazil and worldwide into two clades, which were supported by 99% bootstrap, indicating the presence of two lineages in the state of Maranhão. Variable number of alleles (18, nine, 19) were obtained from three microsatellite loci (T3A7, 3472, C2A8, respectively), by genotyping 237 specimens from 11 populations from the mid-northern region. The analyses detected 12 private alleles, but only ten alleles had frequency lower than 5%. All loci (T3A7, 3472, C2A8) showed significant deviation to Hardy-Weinberg equilibrium (HWE). The observed heterozygosity (Ho) ranged from 0.036 to 1.000, and the expected heterozygosity (He) ranged from 0.185 to 0.876. The coefficient of inbreeding (FIS) showed excessive heterozygotes (negative value of f) in all of the loci analyzed in some populations. The AMOVA indicated greater genetic variation within populations (76% - FST = 0.175), with significant P (<0.001). The paired values of FST for the analysis of microsatellites suggested restricted gene flow between populations, indicating population structuration. The distinct levels of genetic differentiation observed in the populations of Ae. aegypti point out for the necessity of new strategies to its control. The intense chemical treatments and the pressure caused by such prevention programs during the last decades favor the occurrence of mutations, and consequently greater adaptation of the vector mosquito to the environment.