A supergene affects steroid metabolism during early ontogeny in a bird
with alternative reproductive morphs
Reproductive phenotypes are shaped by genetic, physiological and
environmental variation that an organism experiences during ontogeny.
Steroid hormones play an integrative role in this process through both
genomic and non-genomic pathways. Differences in steroid hormone
metabolism may be rooted in genomic variation. Here we evaluate the
influence of supergene variants underlying alternative reproductive
tactics on sex steroid metabolism during ontogeny in ruffs (Calidris
pugnax). Adult ruff males exhibit three male mating morphs called
Independents, Faeders and Satellites, that differ prominently in
circulating androgen (testosterone and androstenedione) concentrations.
Across morphs and sexes chicks showed similar mean androgen
concentrations during ontogenetic development. However, variances in
circulating androgens showed the same pattern as corresponding variances
previously observed in adults. HSD17B2 had been previously identified as
a key gene for mediating differences in androgen levels between morphs
as it encodes the enzyme that converts testosterone to androstenedione
and is located within the supergene. Observed HSD17B2 expression in
embryonic brain tissue was consistent with predictions based on genetic
and endocrine differences. Taken together, the observed differences in
circulating androgen concentrations and gene expression point to
testosterone synthesis as a key mechanism that shapes developmental
trajectories and differences in brain organization among morphs.