Expression profiles of male and female Drosophila melanogaster with X-chromosomes that were subjected to male-limited evolution

Due to its hemizygous mode of inheritance and role in sex determination, the X chromosome is expected to play an important role in the evolution of sexual dimorphism, and to be enriched for sexually antagonistic genetic variation. By forcing the X chromosome to only be expressed in males over many generations, we changed the selection pressures on the X to become similar to those experienced by the Y chromosome. This releases the X from any constraints arising from selection in females, and is predicted to lead to specialization for male fitness, including masculinization of phenotypes that normally experience sexually antagonistic selection. Indeed, we found evidence of this via upregulation of male-benefit sexually antagonistic genes, and downregulation of X-linked female benefit genes. Interestingly, we could detect evidence of microevolutionary changes consistent with previously documented patterns of macroevolutionary change, such as changes in expression consistent with previously established patterns of sexual dimorphism, an increase in the expression of metabolic genes related to mitonuclear conflict, and evidence that dosage compensation constitutes a constraint for male-benefit genes. These results confirm the importance of the X in the evolution of sexual dimorphism and as a source for sexually antagonistic genetic variation, and demonstrate that experimental evolution can be a fruitful method for testing theories of sex chromosome evolution. Microarray data was used to detect differences in gene expression as result of experimental evolution. 24 samples were analyzed. Two treatments with three replicate populations in each treatment, two sexes in each replicate population, two technical replicates for each group (2 treatments x 3 populations x 2 sexes x 2 technical replicates = 24 samples in total).