Strong selective sweep associated with a transposon insertion in Drosophila simulans. T.A. Schlenke 1, D.J. Begun 2. 1) Dept Molec Biol & Genetics, Cornell Univ, Ithaca, NY; 2) Section of Evolution & Ecology, UC Davis, Davis, CA.
We are ignorant of several properties of beneficial mutations, including their mutational origin, their phenotypic effects, and the frequency with which they fix. Here we present population genetic data from several loci across chromosome arm 2R in Drosophila simulans, a highly polymorphic species. A 100 kb segment from a freely recombining genomic region has extremely reduced heterozygosity in a California population, yet typical levels of divergence between species, suggesting that at least one episode of strong directional selection has occurred in the sampled area. The 5-flanking sequence of one gene from this region, Cyp6g1 (a cytochrome P450), is nearly fixed for a Doc transposable element insertion. This D. simulans Doc element is correlated with increased transcript abundance of Cyp6g1, a phenotype previously shown to be associated with DDT resistance in D. melanogaster. Surveys of the same genomic region in an African D. simulans population revealed no evidence for a high-frequency Doc element and no evidence for reduced polymorphism. The population-specific frequency of the Doc element, the corresponding lack of linked variation, and the phenotypic effect on gene expression suggests that the Doc element is a beneficial mutation. The data from D. simulans are paralleled in some respects by data from D. melanogaster showing the high-frequency insertion of an Accord (Gypsy-like) transposable element upstream of Cyp6g1.