Abstract For sex-specific ornaments to be expressed only at a particular ontogenetic stage, genetic correlations between the sexes and between ontogenetic stages should be resolved. In vertebrates, sex-specific and ontogenetic stage-specific expression of sexual dimorphism is often mediated by sex steroid signalling. Here, we investigated the epigenetic mechanisms by which androgen induces sex-specific gene expression that may be involved in male-specific nuptial colouration in the three-spined stickleback (Gasterosteus aculeatus). First, we identified several androgen-responsive genes in skin tissues from the throat and ventral side of the body. The Tetratricopeptide repeat domain 39b (Ttc39b) gene, which is involved in the expression of red colouration in other vertebrates, was up-regulated in throat skin after androgen treatment. We also found that the Growth regulation by estrogen in breast cancer 1-like (Greb1l) gene, whose homologue is involved in the amplification of androgen signalling in human cancer cells, was up-regulated in both tissues after androgen treatment. Some gene-expression changes induced by the androgen treatment, including the change in Greb1l expression, were associated with changes in chromatin accessibility, as determined using assay for transposase-accessible chromatin using sequencing (ATAC-seq). These results suggest that at least some of the sex- and ontogenetic stage-specific gene expression may be achieved by epigenetic changes in chromatin accessibility. This article is part of the theme issue ‘Ecological epigenetics at the intersection of behaviour and life history variation in non-model animals’.
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