Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

Abstract

Many animals extract, synthesize and refine chemicals for colour display, where a range of compounds and structures can produce a diverse colour palette. Feather colours, for example, span the visible spectrum and mostly result from pigments in five chemical classes (carotenoids, melanins, porphyrins, psittacofulvins and metal oxides). However, the pigment that generates the yellow colour of penguin feathers appears to represent a sixth, poorly characterized class of feather pigments. This pigment class, here termed 'spheniscin', is displayed by half of the living penguin genera; the larger and richer colour displays of the pigment are highly attractive. Using Raman and mid-infrared spectroscopies, we analysed yellow feathers from two penguin species (king penguin, Aptenodytes patagonicus; macaroni penguin, Eudyptes chrysolophus) to further characterize spheniscin pigments. The Raman spectrum of spheniscin is distinct from spectra of other feather pigments and exhibits 17 distinctive spectral bands between 300 and 1700 cm 21 . Spectral bands from the yellow pigment are assigned to aromatically bound carbon atoms, and to skeletal modes in an aromatic, heterocyclic ring. It has been suggested that the penguin pigment is a pterin compound; Raman spectra from yellow penguin feathers are broadly consistent with previously reported pterin spectra, although we have not matched it to any known compound. Raman spectroscopy can provide a rapid and non-destructive method for surveying the distribution of different classes of feather pigments in the avian family tree, and for correlating the chemistry of spheniscin with compounds analysed elsewhere. We suggest that the sixth class of feather pigments may have evolved in a stem-lineage penguin and endowed modern penguins with a costly plumage trait that appears to be chemically unique among birds.

Dispersive Raman spectroscopy allows the identification and quantification of melanin types

“…Additionally, results in Thomas et al. (2013) conflict with the ones reported by Galván et al. (2013b), who characterized the Raman spectrum of pheomelanin, again not including fluorescence but wide Raman bands at about 500, 1490, and 2000 cm −1 (Galván et al.…”

“…They therefore concluded that this fluorescence response is diagnostic for melanins (Thomas et al. 2013). In another study, feathers excited with a 1064-nm laser resulted in a Raman band around 1100 nm that was assigned to melanin (Thomas et al.…”

“…Therefore, Thomas et al. 's (2013) main conclusion may not be right, as fluorescence disturbances are not the characteristic features of melanins when analyzed by Raman spectroscopy, but defined Raman bands can be found in both eumelanin and pheomelanin, including when these pigments are analyzed in feathers. Additionally, the Raman band around 1100 nm assigned by Thomas et al.…”

Spiders have rich pigmentary and structural colour palettes

“…In contrast, Raman spectroscopy provides a non-destructive, fast and easy way to identify pigments in situ with almost no sample preparation. With Raman spectroscopy, pigmentary colours can be readily categorized into one of the few more common groups of pigments by comparing their Raman signature signals to expedite further biochemical analyses using HPLC and/or MS. Raman spectroscopy has identified many different types of pigments in bird feathers (Galván et al, 2013;Thomas and James, 2016;Thomas et al, 2013) but has rarely been applied to spiders. Thus, we developed a workflow that begins with Raman spectroscopy to evaluate long-standing assumptions about pigmentary colours in spiders.…”

Nondestructive Raman spectroscopy confirms carotenoid-pigmented plumage in the Pink-headed Duck

“…Mechanisms for accumulating at least 6 chemically distinct groups of pigments in feathers have evolved within birds or their nonavian ancestors (McGraw 2006b, Thomas et al 2013. Carotenoid plumage pigments (red, orange, yellow, pink, purple) are honest signals of fitness for some species (Hill 1990) and apparently have multiple, ancient origins (Thomas et al 2014a).…”