Gene expression polymorphism in Drosophila populations.

Although changes in gene expression have long been recognized as critical to evolutionary processes, the extent of natural polymorphism in gene expression has yet to be assessed, thus opening a new area of active research. We present microarray and quantitative real-time polymerase chain reaction (RT-PCR) data from Cosmopolitan and Zimbabwe morphs of Drosophila melanogaster. These morphs provide a useful model for investigations into the incipient stages of speciation because Zimbabwe females tend to preferentially mate with their own males and discriminate against Cosmopolitan males, while Cosmopolitan females mate indiscriminately. We analysed expression profiles from heads of mated and nonmated females and identified 45 candidate genes whose expression levels were associated with the behavioural morphs and were modified by mating. Genes with altered transcription levels were randomly distributed across the genome and fell into diverse categories of biological activities. Several candidate genes, such as desaturase2 and Odorant receptor 63a, were additionally subjected to quantitative RT-PCR analysis. Notably, desaturase2, which has been invoked to play a role in sexual isolation between Cosmopolitan and Zimbabwe D. melanogaster/races/strains and predicted to be translational-inactive in Cosmopolitan due to a major deletion, was found to be up-regulated in Zimbabwe and down-regulated, but still expressed, in Cosmopolitan.