Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer

The iridescent plumage of many birds is structurally colored due to an orderly arrangement of melanosomes in their feather barbules. Here, we investigated the blue- to purple-colored feathers of the European starling (Sturnus vulgaris) and the blue and green feathers of the Cape starling (Lamprotorn...

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Autores principales:	Pascal Freyer, Bodo D. Wilts, Doekele G. Stavenga
Formato:	article
Lenguaje:	EN
Publicado:	Frontiers Media S.A. 2021
Materias:	refractive index effective medium approach multilayer modeling keratin melanin directional reflectance Evolution QH359-425 Ecology QH540-549.5
Acceso en línea:	https://doaj.org/article/cb39edbc93534fce9c49ce300aea687c
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spelling	oai:doaj.org-article:cb39edbc93534fce9c49ce300aea687c2021-11-19T06:50:47ZCortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer2296-701X10.3389/fevo.2021.746254https://doaj.org/article/cb39edbc93534fce9c49ce300aea687c2021-11-01T00:00:00Zhttps://www.frontiersin.org/articles/10.3389/fevo.2021.746254/fullhttps://doaj.org/toc/2296-701XThe iridescent plumage of many birds is structurally colored due to an orderly arrangement of melanosomes in their feather barbules. Here, we investigated the blue- to purple-colored feathers of the European starling (Sturnus vulgaris) and the blue and green feathers of the Cape starling (Lamprotornis nitens). In both cases, the barbules contain essentially a single layer of melanosomes, but in S. vulgaris they are solid and rod-shaped, and in L. nitens they are hollow and rod- as well as platelet-shaped. We analyzed the coloration of the feathers by applying imaging scatterometry, bifurcated-probe- and micro-spectrophotometry. The reflectance spectra of the feathers of the European starling showed multiple peaks and a distinct, single peak for the Cape starling feathers. Assuming that the barbules of the two starling species contain a simple multilayer, consisting locally only of a cortex plus a single layer of melanosomes, we interpret the experimental data by applying effective-medium-multilayer modeling. The optical modeling provides quantitative insight into the function of the keratin cortex thickness, being the principal factor to determine the peak wavelength of the reflectance bands; the melanosome layer only plays a minor role. The air cavity in the hollow melanosomes of the Cape starling creates a strongly enhanced refractive index contrast, thus very effectively causing a high reflectance.Pascal FreyerBodo D. WiltsDoekele G. StavengaFrontiers Media S.A.articlerefractive indexeffective medium approachmultilayer modelingkeratinmelanindirectional reflectanceEvolutionQH359-425EcologyQH540-549.5ENFrontiers in Ecology and Evolution, Vol 9 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	refractive index effective medium approach multilayer modeling keratin melanin directional reflectance Evolution QH359-425 Ecology QH540-549.5
spellingShingle	refractive index effective medium approach multilayer modeling keratin melanin directional reflectance Evolution QH359-425 Ecology QH540-549.5 Pascal Freyer Bodo D. Wilts Doekele G. Stavenga Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
description	The iridescent plumage of many birds is structurally colored due to an orderly arrangement of melanosomes in their feather barbules. Here, we investigated the blue- to purple-colored feathers of the European starling (Sturnus vulgaris) and the blue and green feathers of the Cape starling (Lamprotornis nitens). In both cases, the barbules contain essentially a single layer of melanosomes, but in S. vulgaris they are solid and rod-shaped, and in L. nitens they are hollow and rod- as well as platelet-shaped. We analyzed the coloration of the feathers by applying imaging scatterometry, bifurcated-probe- and micro-spectrophotometry. The reflectance spectra of the feathers of the European starling showed multiple peaks and a distinct, single peak for the Cape starling feathers. Assuming that the barbules of the two starling species contain a simple multilayer, consisting locally only of a cortex plus a single layer of melanosomes, we interpret the experimental data by applying effective-medium-multilayer modeling. The optical modeling provides quantitative insight into the function of the keratin cortex thickness, being the principal factor to determine the peak wavelength of the reflectance bands; the melanosome layer only plays a minor role. The air cavity in the hollow melanosomes of the Cape starling creates a strongly enhanced refractive index contrast, thus very effectively causing a high reflectance.
format	article
author	Pascal Freyer Bodo D. Wilts Doekele G. Stavenga
author_facet	Pascal Freyer Bodo D. Wilts Doekele G. Stavenga
author_sort	Pascal Freyer
title	Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
title_short	Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
title_full	Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
title_fullStr	Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
title_full_unstemmed	Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer
title_sort	cortex thickness is key for the colors of iridescent starling feather barbules with a single, organized melanosome layer
publisher	Frontiers Media S.A.
publishDate	2021
url	https://doaj.org/article/cb39edbc93534fce9c49ce300aea687c
work_keys_str_mv	AT pascalfreyer cortexthicknessiskeyforthecolorsofiridescentstarlingfeatherbarbuleswithasingleorganizedmelanosomelayer AT bododwilts cortexthicknessiskeyforthecolorsofiridescentstarlingfeatherbarbuleswithasingleorganizedmelanosomelayer AT doekelegstavenga cortexthicknessiskeyforthecolorsofiridescentstarlingfeatherbarbuleswithasingleorganizedmelanosomelayer
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Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer

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