ABSTRACT
The costs associated with the production and maintenance of colour patches is thought to maintain their honesty. Although considerable research on sexual selection has focused on structurally coloured plumage ornaments, the proximate mechanisms of their potential condition dependence, and thus their honesty, is rarely addressed, particularly in an experimental context. Blue tit (Cyanistes caeruleus) nestlings have ultraviolet (UV)–blue structurally coloured tail feathers, providing a unique opportunity for investigation of the causes of variation in their colour. Here, we examined the influence of early growing conditions on the reflectance and structural properties of UV–blue-coloured tail feathers of blue tit nestlings. We applied a two-stage brood size manipulation to determine which stage of development more strongly impacts the quality of tail feather colouration and microstructure. We used small-angle X-ray scattering (SAXS) and electron microscopy to characterise the nanoscale and microscale structure of tail feather barbs. Nestlings from the broods enlarged at a later stage of growth showed a sex-specific rectrix development delay, with males being more sensitive to this manipulation. Contrary to predictions, treatment affected neither the quality of the barbs’ nanostructures nor the brightness and UV chroma of feathers. However, at the microscale, barbs’ keratin characteristics were impaired in late-enlarged broods. Our results suggest that nanostructure quality, which determines the UV–blue colour in tail feathers, is not sensitive to early rearing conditions. Furthermore, availability of resources during feather growth seems to impact the quality of feather microstructure more than body condition, which is likely to be determined at an earlier stage of nestling growth.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: K.J., M.D.S., M.C., S.M.D.; Methodology: K.J., A.P., M.D.S., S.M.D.; Software: K.J.; Validation: S.M.D.; Formal analysis: K.J., S.M.D.; Investigation: K.J., A.Ł., A.P., D.L., J.B., S.M.D.; Resources: K.J., A.Ł., A.P., L.G., S.M.D.; Data curation: K.J., A.P., S.M.D.; Writing - original draft: K.J.; Writing - review & editing: A.Ł., A.P., D.L., J.B., M.D.S., L.G., M.C., S.M.D.; Visualization: K.J., A.P.; Supervision: M.C., S.M.D.; Project administration: K.J.; Funding acquisition: K.J., M.D.S., S.M.D.
Funding
This study was financed by Narodowe Centrum Nauki [UMO-2015/19/N/NZ8/00404 to K.J.; UMO-2015/18/E/NZ8/00505 to S.M.D.] and by Fonds Wetenschappelijk Onderzoek [G007117N to M.D.S.].
Data availability
Data sets used in quantitative analyses are available from the figshare data repository: https://doi.org/10.6084/m9.figshare.12732971.v1
Supplementary information
Supplementary information available online at https://jeb.biologists.org/lookup/doi/10.1242/jeb.228387.supplemental
- Received May 6, 2020.
- Accepted July 28, 2020.
- © 2020. Published by The Company of Biologists Ltd
Log in using your username and password
Log in through your institution
Pay Per Article - You may access this article (from the computer you are currently using) for 1 day for US$30.00 .
Regain Access - You can regain access to a recent Pay per Article purchase if your access period has not yet expired.