Abstract
The Drosophila melanogaster 91-R and 91-C strains are of common origin, however, 91-R has been intensely selected for dichlorodiphenyltrichloroethane (DDT) resistance over six decades while 91-C has been maintained as the non-selected control strain. These fly strains represent a unique genetic resource to understand the accumulation and fixation of mutations under laboratory conditions over decades of pesticide selection. Considerable research has been done to investigate the differential expression of genes associated with the highly DDT resistant strain 91-R, however, with the advent of whole genome sequencing we can now begin to develop an in depth understanding of the genomic changes associated with this intense decades-long xenobiotic selection pressure. Here we present the first whole genome sequencing analysis of the 91-R and 91-C fly strains to identify genome-wide structural changes within the open reading frames. Between-strain changes in allele frequencies revealed a higher percent of new alleles going to fixation for the 91-R strain, as compared to 91-C (P<0.0001). These results suggest that resistance to DDT in the 91-R laboratory strain could potentially be due primarily to new mutations, as well as being polygenic rather than the result of a few major mutations, two hypotheses that remain to be tested.
Highlights
The organochlorine insecticide dichlorodiphenyltrichloroethane (DDT) disrupts arthropod nervous system function by affecting nerve cell plasma membrane permeability and causing paralysis [1]
The chemical was used for control of insect pest populations starting in the 1940s, but instances of field resistance were observed in many species including Drosophila melanogaster (Drosophila) [2]
In terms of the allele frequency distribution, we were able to unfold the distribution rather than working with minor allele frequency (MAF), i.e. ancestral alleles found in D. melanogaster will be similar to the D. simulans reference while new mutations will be dissimilar and usually only found in the D. melanogaster population
Summary
The organochlorine insecticide dichlorodiphenyltrichloroethane (DDT) disrupts arthropod nervous system function by affecting nerve cell plasma membrane permeability and causing paralysis [1]. The chemical was used for control of insect pest populations starting in the 1940s, but instances of field resistance were observed in many species including Drosophila melanogaster (Drosophila) [2]. DDT remains in industrial production due to its continued use for the control of malaria vectoring insects [6], and still persists in many ecosystems where it has been associated with negative effects on human health [7,8,9]. Despite the elimination of selection pressures in many nations, resistance traits persist within endemic pest populations and may remain at high frequencies due to random genetic drift on alleles that have no fitness cost [10]. Selection on insect populations through the use of DDT has been an important man-made evolutionary force
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