The nucleotide changes governing cuticular hydrocarbon variation and theirevolution in Drosophila melanogaster

The cuticular hydrocarbon (CH) pheromones in Drosophila melanogaster exhibi t strong geographic variation. African and Caribbean populations have a hig h ratio of 5.9 heptacosadiene/7,11 heptacosadiene (the "High" CH type), whe reas populations from all other areas have a low ratio ("Low" CH type). Bas ed on previous genetic mapping, DNA markers were developed that localized t he genetic basis of this CH polymorphism to within a 13-kb region. We then carried out a hierarchical search for diagnostic nucleotide sites starting with four lines, and increasing to 24 and 43 lines from a worldwide collect ion. Within the 13-kb region, only one variable site shows a complete conco rdance with the CH phenotype. This is a 16-bp deletion in the 5' region of a desaturase gene (desat2) that was recently suggested to be responsible fo r the CH polymorphism on the basis of its expression [Dallerac, R., Labeur, C., Jallon, J.-M., Knipple, D, C., Roelofs, W. L. & Wicker-Thomas, C. (200 0) Proc. Natl. Acad. Sci. 97, 9449-9454]. The cosmopolitan Low type is deri ved from the ancestral High type, and DNA sequence variations suggest that the former spread worldwide with the aid of positive selection. Whether thi s CH variation could be a component of the sexual isolation between Zimbabw e and other cosmopolitan populations remains an interesting and unresolved question.