YNot a Dead End: Epistatic Interactions BetweenY-Linked Regulatory Polymorphisms and Genetic Background Affect Global Gene Expression inDrosophila melanogaster

The Y chromosome, inherited without meiotic recombination from father to son, carries relatively few genes in most species. This is consistent with predictions from evolutionary theory that nonrecombining chromosomes lack variation and degenerate rapidly. However, recent work has suggested a dynamic role for the Y chromosome in gene regulation, a finding with important implications for spermatogenesis and male fitness. We studied Y chromosomes from two populations of Drosophila melanogaster that had previously been shown to have major effects on the thermal tolerance of spermatogenesis. We show that these Y chromosomes differentially modify the expression of hundreds of autosomal and X-linked genes. Genes showing Y-linked regulatory variation (YRV) also show an association with immune response and pheromone detection. Indeed, genes located proximal to the euchromatin-heterochromatin boundary of the X chromosome appear particularly responsive to Y-linked variation, including a substantial number of odorant-binding genes. Furthermore, the data show significant regulatory interactions between the Y chromosome and the genetic background of autosomes and X chromosome. Altogether, our findings support the view that interpopulation, Y-linked regulatory polymorphisms can differentially modulate the expression of many genes important to male fitness, and they also point to complex interactions between the Y chromosome and genetic background affecting global gene expression.