Molecular evolution of sex-biased genes in the Drosophila ananassae subgroup

Genes with sex-biased expression often show rapid molecular evolution between species. Previous population genetic and comparative genomic studies of Drosophila melanogaster and D. simulans revealed that male-biased genes have especially high rates of adaptive evolution. To test if this is also the case for other lineages within the melanogaster group, we investigated gene expression in D. ananassae, a species that occurs in structured populations in tropical and subtropical regions. We used custom-made microarrays and published microarray data to characterize the sex-biased expression of 129 D. ananassae genes whose D. melanogaster orthologs had been classified previously as male-biased, female-biased, or unbiased in their expression and had been studied extensively at the population-genetic level. In total, 12 arrays were analyzed. These arrays include 4 biological replicates for strain KK1 (Kota Kinabalu, Malaysia) + 4 dye-swaps, and 2 biological replicates for strain KK2 (Kota Kinabalu, Malaysia) + 2 dye-swaps.