Signatures of selection and sex-specific expression variation of a novel duplicate during the evolution of the Drosophila desaturase gene family

The tempo and mode of evolution of loci with a large effect on adaptation and reproductive isolation will influence the rate of evolutionary divergence and speciation. Desaturase loci are involved in key biochemical changes in long-chain fatty acids. In insects, these have been shown to influence adaptation to starvation or desiccation resistance and in some cases act as important pheromones. The desaturase gene family of Drosophila is known to have evolved by gene duplication and diversification, and at least one locus shows rapid evolution of sex-specific expression variation. Here, we examine the evolution of the gene family in species representing the Drosophila phylogeny. We find that the family includes more loci than have been previously described. Most are represented as single-copy loci, but we also find additional examples of duplications in loci which influence pheromone blends. Most loci show patterns of variation associated with purifying selection, but there are strong signatures of diversifying selection in new duplicates. In the case of a new duplicate of desat1 in the obscura group species, we show that strong selection on the coding sequence is associated with the evolution of sex-specific expression variation. It seems likely that both sexual selection and ecological adaptation have influenced the evolution of this gene family in Drosophila.     

The production of caproic and butyric acids by the methane fermentation of ethyl alcohol

Summary A fermentation of ethyl alcohol under the influence of Methanobacterium Omelianskii and an associated spore-forming bacterium is described in which the alcohol is converted into acetic, butyric and caproic acids. At the same time there occurs a reduction of carbon dioxide to methane. The data provide direct evidence for the formation of butyric and caproic acids by a condensation of a C₂-compound which probably is acetaldehyde.Division of Plant Nutrition, University of California, Berkeley, California. The author takes great pleasure in expressing his indebtedness to Prof. A. J. Kluyver for extending the hospitality of the Delft laboratory and for his interest, encouragement and advice during the progress of the work.