Evidence for genetic hitchhiking effect associated with insecticide resistance in Aedes aegypti

Information on genetic variation within and between populations is critical for understanding the evolutionary history of mosquito populations and disease epidemiology. Previous studies with Drosophila suggest that genetic variation of selectively neutral loci in a large fraction of genome may be constrained by fixation of advantageous mutations associated with hitchhiking effect. This study examined restriction fragment length polymorphisms of four natural Aedes aegypti mosquito populations from Trinidad and Tobago, at 16 loci. These populations have been subjected to organophosphate (OP) insecticide treatments for more than two decades, while dichlor-diphenyltrichlor (DDT) was the insecticide of choice prior to this period. We predicted that genes closely linked to the OP target loci would exhibit reduced genetic variation as a result of the hitchhiking effect associated with intensive OP insecticide selection. We also predicted that genetic variability of the genes conferring resistance to DDT and loci near the target site would be similar to other unlinkded loci. As predicted, reduced genetic variation was found for loci in the general chromosomal region of a putative OP target site, and these loci generally exhibited larger F (ST) values than other random loci. In contrast, the gene conferring resistance to DDT and its linked loci show polymorphisms and genetic differentiation similar to other random loci. The reduced genetic variability and apparent gene deletion in some regions of chromosome 1 likely to reflect the hitchhiking effect associated with OP insecticide selection(AU)

Molecular analysis of population genetic variability and insecticide resistance of the yellow fever mosquito in Trinidad and Tobago - abstract

Spatial patterns of genetic variants in natural populations are the combined effects of various evolutionary forces and demographic structure. Population life history and mating structure have genome-wide effect, but selection, affects only the target loci or closely-linked loci. This study examines the spatial patterns of 4 natural Aedes aegypti populations of Trinidad and Tobago, through registration fragment length polymorphism (RFLP) analysis of 16 genetic loci representative of mosquito genome on 870 individuals. These populations have been subjected to numerous organophosphate (OP) insecticides for more than 2 decades, but have not been subjected to DDT over this period. We predicted that genes closely-linked to the OP target loci would be strongly affected in gene polymorphism, and probably be the most differentiated loci in the genome, but gene flow has homogenized frequencies for the gene conferring resistance to DDT. As predicted, low DNA polymorphisms and gene deletions were found for loci in the general chromosomal region of the OP target site, and these exhibited large scale FST value. The gene conferring resistance to DDT shows similar polymorphisms and genetic differentiation to other loci in the genome. We concluded that gene flow was not sufficiently frequent to prevent genetic differentiation due to genetic drift or selection, but could be a powerful force for the spread of insectide resistance genes. (AU)