Sex-biased gene expression in the northern pipefish (Syngnathus fuscus), a species with male pregnancy, is widespread and linked to tissue specificity

We highlight the potential for different sex-specific selection pressures to be acting on each tissue type as there were widespread differences in the protein classes represented by sex-biased genes across both organs and sexes, although sex-biased genes did not experience stronger episodic selection than unbiased genes. Furthermore, our results support the hypothesis that broad expression can constrain the molecular evolution of a gene. The work presented here supports the potential for sex-biased gene expression to act as a mechanism for phenotypic differentiation between the sexes and increases our knowledge of patterns of gene expression in an unusual group of fishes.