Sexual dimorphism in gene expression: coincidence and population genomics of two forms of differential expression inDrosophila melanogaster

Abstract

AbstractIn most species, selection favours different phenotypes in the two sexes. This type of sexual antagonism can be resolved through the evolution of sexual dimorphism. Sex differences in gene regulation is a proximate mechanism by which this resolution can be achieved. One form of differential gene regulation is sex differences in the amount a gene is expressed, so called sex-biased gene expression (SBGE). Less attention has been given to sexual dimorphism in isoform usage (SDIU), resulting from sex-specific alternative splicing, which may be another way in which conflict between the sexes is resolved. Here, we use RNA-seq data from two tissue types (heads and bodies) from 18 genotypes of adultDrosophila melanogasterto investigate SDIU. In our data, SBGE and SDIU are both much more prevalent in the body than the head. SDIU is less common among sex-biased than unbiased genes in the body, though the opposite pattern occurs in the head. SDIU, but not SBGE, is significantly associated with reduced values of Tajima’sD, possibly indicating that such genes experience positive selection more frequently. SBGE, but not SDIU, is associated with increasedπN/πS, possibly indicating weaker purifying selection. Together, these results are consistent with the idea that the SDIU and SBGE are alternative pathways towards the resolution of conflict between the sexes with distinct evolutionary consequences.