title: Copy number variation and transposable elements feature in recent, ongoing adaptation at the Cyp6g1 locus.
abstract: The increased transcription of the Cyp6g1 gene of Drosophila melanogaster, and consequent resistance to insecticides such as DDT, is a widely cited example of adaptation mediated by cis-regulatory change. A fragment of an Accord transposable element inserted upstream of the Cyp6g1 gene is causally associated with resistance and has spread to high frequencies in populations around the world since the 1940s. Here we report the existence of a natural allelic series at this locus of D. melanogaster, involving copy number variation of Cyp6g1, and two additional transposable element insertions (a P and an HMS-Beagle). We provide evidence that this genetic variation underpins phenotypic variation, as the more derived the allele, the greater the level of DDT resistance. Tracking the spatial and temporal patterns of allele frequency changes indicates that the multiple steps of the allelic series are adaptive. Further, a DDT association study shows that the most resistant allele, Cyp6g1-[BP], is greatly enriched in the top 5% of the phenotypic distribution and accounts for approximately 16% of the underlying phenotypic variation in resistance to DDT. In contrast, copy number variation for another candidate resistance gene, Cyp12d1, is not associated with resistance. Thus the Cyp6g1 locus is a major contributor to DDT resistance in field populations, and evolution at this locus features multiple adaptive steps occurring in rapid succession.
authors.affiliation: Department of Genetics, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Schmidt
authors.forename: Robert T
authors.initials: RT
authors.lastname: Good
authors.forename: Belinda
authors.initials: B
authors.lastname: Appleton
authors.forename: Jayne
authors.initials: J
authors.lastname: Sherrard
authors.forename: Greta C
authors.initials: GC
authors.lastname: Raymant
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bogwitz
authors.forename: Jon
authors.initials: J
authors.lastname: Martin
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Daborn
authors.forename: Mike E
authors.initials: ME
authors.lastname: Goddard
authors.forename: Philip
authors.initials: P
authors.lastname: Batterham
authors.forename: Charles
authors.initials: C
authors.lastname: Robin
mesh_terms: D000220:Adaptation, Biological; D000483:Alleles; D000818:Animals; D030801:Animals, Genetically Modified; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D056915:DNA Copy Number Variations; D004251:DNA Transposable Elements; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics*; D056426:Genetic Loci; D014158:Transcription, Genetic
chemical_list: D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D003577:Cytochrome P-450 Enzyme System; C446928:Cyp6g1 protein, Drosophila