Scalloped wings Is the Lucilia cuprina Notch Homologue and a Candidate for the Modifier of Fitness and Asymmetry of Diazinon Resistance

Abstract

The Scalloped wings (Scl) gene of the Australian sheep blowfly, Lucilia cuprina, is shown to be the homologue of the Drosophila melanogaster Notch gene by comparison at the DNA sequence and genetic levels. A L. cuprina genomic fragment, which shows strong identity with the Notch (N) gene at the molecular level, hybridizes to the location of the Scl gene on polytene chromosomes. The two genes are functionally homologous; the dominant and recessive Notch-like phenotypes produced by mutations in the Scl gene allow these alleles to be classed as N-like or Abruptex-like. The Scl gene is under investigation as a candidate for the fitness and asymmetry Modifier (M) of diazinon resistance. We show that M affects the penetrance of wing and bristle phenotypes associated with two Scl alleles in a manner consistent with the M being an allele of Scl. In addition, we report a phenotypic interaction between the diazinon-resistance mutation, Rop-1, and the same alleles of Scl. We propose that the product of Rop-1, an esterase, may be involved in cell adhesion in developmental processes involving the Scl gene product.

Fitness studies of insecticide resistant strains: lessons learned and future directions

“…In this case, the modifier (which rescued delayed development associated with resistance) was identified because it was on a different linkage group, 63 and because a difference in the fitness of field‐collected resistant strains was noticed over a period of approximately 10 years. It was subsequently reported that resistance to diazinon was conferred by mutations of the carboxylesterase E3, 64 and proposed that Scalloped wings was the fitness modifier 64 . It has been proposed that duplication of ace‐1 in C. pipiens and A. gambiae is another example of a modifier locus (keeping together one copy of the susceptible allele with a copy of the resistant allele to compensate for the poor enzyme activity of the resistant copy against acetylcholine), 65,66 but separating the resistance allele and the modifier for experimental tests of fitness is in that case much more difficult 53 .…”

The Evolutionary Genetics of Canalization

“…For instance, QTL mapping has been successfully applied in mice where QTLs affecting fluctuating asymmetry in skull morphology have been identified (Leamy et al 1998). Similarly, recombination mapping protocols have been used to identify Notch as a candidate gene responsible for the reduction of fluctuating asymmetry in blowflies (Davies et al 1996).…”

“…A well-understood example concerns diazinon insecticide resistance in blowflies, Lucilia cuprina (e.g., Clarke and McKenzie 1987;Davies et al 1996;overview by Clarke 1997). Resistance to diazinon is essentially conferred by the Rop-1 locus and is correlated with increased levels of fluctuating asymmetry in several bristle traits.…”

“…After resistance had become widespread, however, resistant genotypes were no longer selectively disadvantaged in the absence of the insecticide and had similar fitness as susceptible wildtype genotypes. It was found that selection on the genetic background of resistant genotypes had favored an allele whose spread led to increased levels of environmental canalization (Davies et al 1996). This allele is an allele of the Scalloped wings (Scl) locus, a homolog of the Drosophila gene Notch.…”

Competition among growing organs and developmental control of morphological asymmetry

“…Its developmental origin, however, is mostly unclear. There is only one case in which speci¢c genes with a major in£uence on nondirectional asymmetry have been identi¢ed (Davies et al 1996;Batterham et al 1996), and another study reported a number of quantitative trait loci (Leamy et al 1997). But even in these examples, the role of these genes in the development of asymmetry is not fully understood.…”