In males it is frequently testosterone (T) that activates the expression of sexually selected morphological and behavioral displays, but the role of T in regulating similar traits in females is less clear. Here, we combine correlational data with results from T and gonadotropin-releasing hormone (GnRH) manipulations in both sexes to assess the role of T in mediating sexually dimorphic coloration and morphology in the red-backed fairy-wren (Malurus melanocephalus). We show that: (1) natural variation in female expression of ornamental traits (darkened bills and red back feathers) is positively associated with age and circulating androgen titres, (2) females have the capacity to express most male-typical traits in response to exogenous T, including carotenoid-pigmented body plumage, shorter feathers, darkened bill and enlarged cloacal protuberance, but (3) appear constrained in production of male-typical melanin-pigmented plumage, and (4) low androgen levels during the pre-nuptial molt, probably because of low ovarian capacity for steroid production (or luteinizing hormone sensitivity), prevent females from developing male-like ornamentation. Thus, females appear to retain molecular mechanisms for hormonally regulated male-typical ornamentation, although these are rarely activated because of insufficient production of the hormonal signal.
The authors declare no competing or financial interests.
W.R.L. conceived the study and wrote the manuscript; W.R.L. and D.G.B. collected the field and laboratory data and conducted the analyses; H.S. and M.S.W. provided funding and critical oversight on the project; all authors contributed to the writing.
The research was funded by the National Science Foundation (USA) through a grant to M.S.W. and H.S. (no. 0213075) and a graduate traineeship to D.G.B. (no. 0549425).
Data are deposited in the Dryad Digital Repository: http://dx.doi.org/10.5061/dryad.gf46s
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.135384.supplemental
- Received December 11, 2015.
- Accepted July 26, 2016.
- © 2016. Published by The Company of Biologists Ltd