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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] Neves et al (2020) Impairment of mixed melanin-based pigmentation in parrots. J Experim Biol. DOI 10.1242/jeb.225912
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Measuring oxidative stress

Measuring oxidative stress

Oxidative stress affects may exert strong effects on individual health and fitness. Lipid peroxidation products are widely used as markers of oxidative damage in the organism. This paper investigates the relationship between circulating lipids and two common markers of oxidative damage (plasma levels of malondialdehyde –MDA- and hydroperoxides- d-ROMs assay kit-). The study was performed on several bird species belonging to different taxonomic groups and with different diets. In all cases, plasma triglyceride levels positively and significantly correlated with lipid peroxidation markers, explaining between 8% and 34% of their variability. These results indicate that lipid peroxidation markers levels must be statistically controlled for the lipid concentration in the sample in order to avoid undesirable biases and wrong interpretations. informacion[at] Pérez-Rodríguez et al (2015) Measuring oxidative stress: the confounding effect of lipid concentration in measures of lipid peroxidation Physiol. Biochem. Zool 88 3 345-351 DOI: 10.1086/680688