Analysis of Selection Patterns in Germline Stem Cell Genes (Stonewall, Otefin) in Drosophila pseudoobscura

Abstract

Previous experiments have shown two germline stem cell genes, bam and bgcn, to be under strong positive selection in Drosophila melanogaster and Drosophila simulans (Bauer DuMont et al. 2007). This prompted the question of whether the same pattern of selection observed in these two species was present in the germline stem cell genes of other Drosophila lineages? The Aquadro Lab has been sequencing many germline stem cell genes in Drosophila species, and the answer to this question so far has been that some lineages show strong positive selection and some do not. This observation led the Aquadro Lab to begin to test hypotheses about the driver – or drivers – of the positive selection in the germline stem cell genes across some Drosophila lineages. One hypothesis proposed by Bauer DuMont et al. (2007) is that coevolution with pathogens such as the reproductive parasite, Wolbachia pipientis, infecting the germline could be driving this observed selection. This project looked for signs of selection in the germline stem cell genes stonewall and otefin, two genes that have shown signs of positive selection in other Drosophila species, which the Aquadro Lab has previously tested. These two genes were sequenced in Drosophila pseudoobscura, a species of Drosophila that is not currently known to be infected with Wolbachia. This project shows that both genes do not show evidence of long term, repeated positive selection, but both genes do show evidence for a more recent selective sweep.