Sex-biased gene expression, sexual antagonism and levels of genetic diversity in the collared flycatcher (Ficedula albicollis) genome

Theoretical work suggests that sexual conflict should promote the maintenance of genetic diversity by the opposing directions of selection on sexually antagonistic mutations in males and females. This prediction, so far not been empirically tested on a genome-wide scale, could potentially contribute towards genomic heterogeneity in levels of genetic diversity. We used large-scale population genomic and transcriptomic data from the collared flycatcher (Ficedula albicollis) to analyse how sex-biased gene expression – one outcome of sexual conflict – relates to genetic variability. Here, we demonstrate that the extent of sex-biased gene expression of both male-biased and female-biased genes is significantly correlated with levels of nucleotide diversity in gene sequences and that this correlation extends to the overall levels of genomic diversity. We find evidence for balancing selection in sex-biased genes, suggesting that sex-biased gene expression could be seen as a component counteracting the diversity-reducing effects of linked positive and purifying selection. The observation of significant genetic differentiation between males and females for male-biased genes indicates ongoing sexual conflict and sex-specific viability selection, potentially driven by sexual selection. Our results thus provide a new perspective on the long-standing question in evolutionary biology of how genomes can remain so genetically variable in face of strong natural and sexual selection