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Abstract
Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. The role of molecular environment on hue tends to be overlooked as analyses are mostly performed on free pigments extracted from the integument. Here we analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations (and multiple chromophores) in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores. Our findings are consistent with non-isomeric psittacofulvin pigments behaving as a single chromophore in yellow feather barbs, which implies that psittacofulvins are dispersed into a structurally disordered mixture in yellow feathers compared with red feathers. Frequency dispersion in red barbs may instead indicate that pigments are structurally organized through molecule–molecule interactions. Major differences in the hues of parrot feathers are thus associated with differences in the organization of pigments within feathers.
Highlights
This article has been edited by the Royal Society of Chemistry, including the commissioning, peer review process and editorial aspects up to the point of acceptance
Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores
Yellow colours in parrot feathers contain one dominant chromophore and not the multiple chromophores found in red feather barbs, despite the expectation that both red and yellow feathers contain mixtures of non-isomeric pigments
Summary
This article has been edited by the Royal Society of Chemistry, including the commissioning, peer review process and editorial aspects up to the point of acceptance. Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. We analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Pink, red, orange and yellow feather colours in most birds are conferred by carotenoid pigments (e.g. canaries, flamingos), which are extracted from the diet and concentrated at the base of growing feathers [7]. We explore whether colour variation in parrot feathers may or instead be attributed to differences in the structural organization of psittacofulvin pigments in feathers. The visual difference between red and yellow parrot feathers is most likely due to presence or absence of the C20 pigment component, a different oxidation state at the end of the polyene acyl chains, or both . We are presenting a fourth option to the observation made by Cooke et al [13] that ‘ . . . the visual difference between red and yellow parrot feathers is most likely due to presence or absence of the C20 pigment component, a different oxidation state at the end of the polyene acyl chains, or both . . . ’
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