The desaturase gene family : an evolutionary study of putative speciation genes in 12 species of Drosophila

Abstract

The formation and persistence of species are the subject of much debate among biologists. Many species of Drosophila are behaviourally isolated, meaning that heterospecific individuals are not attracted to one another and do not interbreed. Often, this behavioural isolation is at least in part due to differences in pheromonal preference. Drosophila pheromones are long-chain cuticular hydrocarbons (CHCs). Desaturases are enzymes that are important for the production of CHCs. This thesis investigates the evolution of the gene family across 12 species of Drosophila. Desaturase genes were located in all species. Some genes, those that have previously been shown to have important roles in pheromonal communication, have experienced duplication and loss in several species. Two previously undiscovered duplicates were identified. Generally the desaturase gene family is governed by purifying selection, although following duplication these constraints are relaxed and in some cases duplicated genes show compelling evidence of positive selection. One of the loci under positive selection, the novel duplicate desat1b of the obscura group, was found to have a sex-biased expression pattern and alternative splicing in its 5′ UTR. In RNAi knock-down experiments of desaturase gene function in D. melanogaster, several desaturases were shown to affect CHC profiles of males and females, including some that were previously unlinked to CHC production.