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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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The biochemical basis of the sexual ornaments of the red grouse unravels their informative content

The biochemical basis of the sexual ornaments of the red grouse unravels their informative content

The carotenoid-based ornaments displayed by many birds often play key roles in social and sexual signalling, revealing information about individual quality. Understanding the mechanisms of coloured trait production and maintenance requires an accurate description of their composition and of the physiological pathways involved in their expression. Carotenoid-based colouration has been extensively studied in birds, but such information is often lacking for coloured integuments other than feathers, such as fleshy carotenoid based ornaments. Authors report the carotenoid composition of the combs of the red grouse, a sexual trait that honestly reveals individual quality. It was found that comb pigmentation was primarily the result of two red ketocarotenoids (astaxanthin and papilioerythrinone), which are synthesised from their dietary precursors (zeaxanthin and lutein) directly at the comb integument. These red ketocarotenoids are largely deposited esterified with fatty acids. Astaxanthin concentration in the comb was found to negatively correlate with retinol levels but positively correlate with tocopherol levels. Considering evidence from this and other studied species, authors suggest that carotenoid esterification is a characteristic of coloured fleshy integuments, probably affecting pigment stability and colouration in living tissues, with subsequent effects on their signalling role and maintenance costs. Honest signalling via comb colouration appears mostly related to potential allocation trade-offs of some specific dietary precursors or to the capacity of individuals to manage the redox reactions interfering with carotenoid metabolism. informacion[at]ebd.csic.es: Pérez-Rodríguez et al (2016) Carotenoid profile and vitamins in the combs of the red grouse (Lagopus lagopus scoticus): implications for the honesty of a sexual signal. J Ornithol 157:145–153 DOI 10.1007/s10336-015-1261-y


http://link.springer.com/article/10.1007/s10336-015-1261-y