Multiple Mutations and Gene Duplications Conferring Organophosphorus Insecticide Resistance Have Been Selected at the Rop-1 Locus of the Sheep Blowfly, Lucilia cuprina

Abstract

Sequences of the esterase gene alpha E7 were compared across 41 isogenic (IV) strains of the sheep blowfly, Lucilia cuprina, and one strain of the sibling species, L. sericata. The 1.2-kb region sequenced includes sites of two insecticide resistance mutations. Gly137Asp confers resistance to organophosphorus insecticides (OPs), particularly preferring diethyl OPs such as diazinon, while Trp251Leu prefers dimethyl OPs, and particularly malathion, with the additional presence of carboxylester moieties. We found that there are just eight haplotypes among the 41 chromosomes studied: two Gly137Asp containing haplotypes, two Trp251Leu containing haplotypes, and four susceptible haplotypes, including the L. sericata sequence. While phylogenetic analysis of these haplotypes suggests that the Asp137 and Leu251 mutations each arose at least twice, evidence for recombination was detected across the region, therefore single origins for these resistance mutations cannot be ruled out. Levels of linkage disequilibrium in the data are high and significant hitchhiking is indicated by Fay and Wu' s H test but not the Tajima test. A test of haplotype diversity indicates a paucity of diversity compared with neutral expectations. Both these results are consistent with a very recent selective sweep at the Lc alphaE7 locus. Interestingly, gene duplications of three different combinations of OP resistant haplotypes were identified in seven of the isogenic (IV) strains. All three types of duplication involve an Asp137 and a Trp251 haplotype. To examine whether more haplotypes existed before the hypothesised selective sweep, fragments of alpha E7 surrounding the resistance mutations were amplified from pinned material dating back to before OPs were used. Four new sequence haplotypes, not sampled in the survey of extant haplotypes, were obtained that are all associated with susceptibility. This is suggestive of a higher historical level of susceptible allelic diversity at this locus.

Contribution of Gene Amplification to Evolution of Increased Antibiotic Resistance inSalmonella typhimurium

“…Thus, whenever growth is limited by an external factor (e.g., low nutrient levels) or an internal factor (e.g., a deleterious mutation), and the problem may be mitigated by increasing the levels of a gene product, common gene amplifications are likely to be selected. Evidence that this actually occurs is the frequent detections of gene amplification in bacteria during growth on limited carbon sources (Tlsty et al 1984;Sonti and Roth 1989), in the presence of various toxic compounds (Edlund and Normark 1981;Fogel and Welch 1982;Gottesman et al 1995;Newcomb et al 2005), and in mutants with reduced fitness (Nilsson et al 2006;Paulander et al 2007). …”

Seasonal fluctuation in susceptibility to insecticides within natural populations of Drosophila melanogaster. II. Features of genetic variation in susceptibility to organophosphate insecticides within natural populations of D. melanogaster

“…E-mail: tmiyo1@sakura.cc.tsukuba.ac.jp 1997), acetylcholinesterase for organophosphate and carbamate insecticides (Mutero et al, 1994;Menozzi et al, 2004), and the γ -amino butyric acid receptor for cyclodiene insecticides (ffrench-Constant et al, 2004). Increased degradation is exemplified by cytochrome P450s (Daborn et al, 2002;Festucci-Buselli et al, 2005), esterases (Newcomb et al, 2005), and glutathione Stransferases (Enayati et al, 2005).…”

Amplification of DNA from preserved specimens shows blowflies were preadapted for the rapid evolution of insecticide resistance

“…Diazinon resistance is because of a Gly137Asp mutation in E3, which bestows a new OP hydrolase activity on the enzyme, although it abolishes the enzyme's native carboxylesterase activity (11)(12)(13). Malathion resistance is because of a Trp251Leu mutation, which confers a lower level of OP hydrolase activity but has much less effect on carboxylesterase activity (13)(14)(15). The Asp-137 enzyme is more active on OPs such as diazinon that have diethyl, rather than dimethyl substituents, and this biochemical preference corresponds with higher resistance ratios in flies treated with these compounds.…”