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Impairment of mixed melanin-based pigmentation in parrots

Parrots and allies (Order Psittaciformes) have evolved an exclusive capacity to synthesize polyene pigments called psittacofulvins at feather follicles, which allows them to produce a striking diversity of pigmentation phenotypes. Melanins are polymers constituting the most abundant pigments in animals, and the sulphurated form (pheomelanin) produces colors that are similar to those produced by psittacofulvins. However, the differential contribution of these pigments to psittaciform phenotypic diversity has not been investigated. Given the color redundancy, and physiological limitations associated to pheomelanin synthesis, this study assumed that the latter would be avoided by psittaciform birds. This hypothesis was tested by using Raman spectroscopy to identify pigments in feathers exhibiting colors suspicious of being produced by pheomelanin (i.e., dull red, yellow and grey- and green-brownish) in 26 species from the three main lineages of Psittaciformes. The non-sulphurated melanin form (eumelanin) were detected in black, grey and brown plumage patches, and psittacofulvins in red, yellow and green patches, but no evidence of pheomelanin was found. As natural melanins are assumed to be composed of eumelanin and pheomelanin in varying ratios, these results represent the first report of impairment of mixed melanin-based pigmentation in animals. Given that psittaciforms also avoid the uptake of circulating carotenoid pigments, these birds seem to have evolved a capacity to avoid functional redundancy between pigments, likely by regulating follicular gene expression. The study provides the first vibrational characterization of different psittacofulvin-based colors and thus helps to determine the relative polyene chain length in these pigments, which is related to their antireductant protection activity. informacion[at]ebd.csic.es: Neves et al (2020) Impairment of mixed melanin-based pigmentation in parrots. J Experim Biol. DOI 10.1242/jeb.225912


https://jeb.biologists.org/content/early/2020/05/08/jeb.225912
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Molecular vibration as a novel explanatory mechanism for the expression of animal colouration

Molecular vibration as a novel explanatory mechanism for the expression of animal colouration

Animal colouration is characterized by the concentration of pigments in integumentary structures and by the nanoscale arrangement of constitutive elements. However, the influence of molecular vibration on colour expression has been overlooked in biology. Molecular vibration occurs in the infrared spectral region, but vibrational and electronic properties can influence each other. Thus, the vibration of pigment molecules may also affect their absorption properties and the resulting colours. For the first time the relative contribution of molecular vibration (by means of Raman spectroscopy) and concentration (by means of HPLC) of melanin polymers, the most common animal pigments, was calculated to generate diversity in plumage colour in 47 species of birds. Vibrational characteristics explained >9 times more variance in colour expression than the concentration of melanins. Additionally, melanin Raman spectra was modelled on the basis of the chemical structure of their constituent monomers and calculated the Huang-Rhys factors for each vibrational mode, which indicate the contribution of these modes to the electronic spectra responsible for the resulting colours. High Huang-Rhys factors frequently coincided with the vibrational modes of melanin monomers. Results can be explained by the influence of molecular vibration on the absorption properties of melanins. The colour of organisms may thus mainly result from the vibrational properties of their molecules and only residually from their concentration. As a given melanin concentration can give rise to different colours because different structural melanin conformations can present different vibrational characteristics, vibrational effects may favour phenotypic plasticity and thus constitute an important evolutionary force. informacion[at]ebd.csic.es: Galvan et al (2018) Molecular vibration as a novel explanatory mechanism for the expression of animal colouration. Integrative Biol. Doi 10.1039/C8IB00100F


http://pubs.rsc.org/en/content/articlelanding/2018/ib/c8ib00100f#!divAbstract