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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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Context-dependent effects of yolk androgens on nestling performance

Context-dependent effects of yolk androgens on nestling performance

Maternal effects have a great influence on offspring phenotype. In oviparous species, females can adjust offspring development by changing the levels of certain components of the egg (like yolk hormones, particularly androgens), thus buffering the impacts of environmental heterogeneity on the performance of their descendants. Several studies have reported short term benefits of high yolk androgen levels, but such high hormone levels can also entail some costs, particularly those associated to decreased immunocompetence. In this research article it is shown that the resolution of this conflict is context-dependent. Thus, it was found that the effects of androgens on growth, immune function and survival of spotless starling chicks vary depending on the environment in which they develop. Overall, a positive effect of increased androgen levels was found in early clutches, whereas a negative balance (i.e. decreased immunocompetence and increased mortality) was found in clutches laid later in the season, when environmental conditions are harsher. The contrasted environmental conditions that the different broods of the species experience within the same breeding season determines why females should accurately and adaptively adjust their androgen allocation to egg yolks. informacion[at] Muriel et al (2015) Context-dependent effects of yolk androgens on nestling growth and immune function in a multibrooded passerine J Evol Biol 28 ( 2 0 15 ) 1476–1488 doi: 10.1111/jeb.12668