Differential effects of early growth conditions on colour-producing nanostructures revealed through small angle X-ray scattering (SAXS) and electron microscopy

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.

Sexual dichromatism, size dimorphism, and microscale anatomy of white wing stripe in blue tits

“…Thus, the mechanism of the structural color production in this patch is analogous to the 1 found in the blue tit crown and tail feathers ( Hegyi et al. 2018 ; Janas et al. 2020 ).…”

The mechanistic basis of evolutionary transitions between grey, slate, and blue colour in Tanagers (Thraupidae)

“…Namely, artificial shrinkage of the samples during the sample preparation as well as time-consuming sample preparation. In contrast, SAXS requires no sample prep, beyond mounting the sample in the path of the beam (Saranathan et al, 2012; Janas et al, 2020; Parnell et al, 2015).…”

Long-Term Decrease in Coloration: A Consequence of Climate Change?

“…On the other hand, structural colourations are less costly to produce (Prum et al 2009) and their expression constraints may be more indirectly linked to the environment (e.g. feather development time; Griggio et al 2009), thus they are expected to be less reactive to environmental variation (Prum 2006;Janas et al 2020). However, all colourations present some degree of environmental dependence, and can be driven by the inter-annual variation in climatic conditions (e.g.…”