Melanin Basis of Ornamental Feather Colors in Male Zebra Finches

Abstract

The carotenoid-pigmented bill of Zebra Finches (Taeniopygia guttata) has received much recent attention as a sexually selected signal of quality, but these birds also display several sexually dichromatic plumage traits, including rust-colored cheek patches, a black breast band, and brown flanks. Black, brown, and earth-toned features in animals are thought to be produced by melanin pigments, but few studies have identified the melanin content of such colors in bird feathers. We used a series of biochemical techniques to investigate the pigmentary basis of these plumage colors in male Zebra Finches. All three feather traits contained melanin pigments, but varied in the amounts of the two basic forms of melanin (eumelanin and phaeomelanin). Black breast feathers contained predominantly eumelanin, whereas cheek and flank feathers contained extraordinarily high concentrations of phaeomelanin. Conventional methods of carotenoid analysis detected no carotenoids in either the cheek or flank feathers. Coloración Basada en Melaninas en las Plumas Ornamentales de los Machos de Taeniopygia guttata Resumen. El pico pigmentado con carotenoides de Taeniopygia guttata ha sido destacado recientemente como una señal de calidad seleccionada sexualmente, pero estas aves también presentan varios caracteres de plumaje sexualmente dicromáticos, incluyendo parches en las mejillas de color óxido, una faja pectoral negra y flancos de color café. Se cree que las tonalidades negras, cafés y color tierra son producidas por melaninas en los animales, pero existen pocos estudios que hayan identificado el contenido de melanina de dichos colores en las plumas de las aves. En este estudio empleamos una serie de técnicas bioquímicas para investigar la base pigmentaria de estos colores del plumaje en machos de T. guttata. Los tres caracteres de las plumas contaron con pigmentos melánicos, pero variaron en las cantidades de las dos formas básicas de melanina (eumelanina y feomelanina). Las plumas negras del pecho presentaron principalmente eumelanina, mientras que las de las mejillas y los flancos presentaron concentraciones extraordinariamente altas de feomelanina. Los métodos tradicionales de análisis de carotenoides no detectaron este tipo de pigmentos en las plumas de las mejillas y los flancos.

Stressful Dieting: Nutritional Conditions but Not Compensatory Growth Elevate Corticosterone Levels in Zebra Finch Nestlings and Fledglings

“…The lack of nutritional effects on male cheek development underlines that timing and duration of dietary restrictions matter. Cheek ornamentation is melanin-based containing 99.2% phaemelanin and 0.8% eumelanin [49] and even though its synthesis was recently shown to be affected by dietary manipulations [50] it is considered to be energetically cheap [51]. Our findings expand on these studies by showing that the expression of plumage ornaments is not affected by dietary history, whereas nutritional condition during the actual development of the ornaments affects their expression [52].…”

MC1R Genotype and Plumage Colouration in the Zebra Finch (Taeniopygia guttata): Population Structure Generates Artefactual Associations

“…Given the large number of studies reporting associations between MC1R genotype and coloration [8] and the fact that the white zebra finch phenotype clearly reflects a lack of melanin [13], we were surprised to find no association between MC1R genotype and plumage colouration. However, our data do not allow us to definitively rule out a role for MC1R , partly because we were unable to recover high quality sequence data for a small portion of the coding region (26/945 bp), but also because substitutions in MC1R regulatory regions could also be involved [8].…”

“…A good candidate for further study is the black cheek morph, where the orange cheek patch in the male is instead black and females gain a black cheek patch. This particular trait is limited to a small region of plumage, it can be explained by differences in melanin deposition [13] and its expression is not sex-dependent. It may therefore have a different genetic basis to the white morph since the latter lacks multiple melanin-based ornaments, potentially implicating changes at the regulatory level.…”

“…Wild type zebra finches carry melanin based plumage ornaments that differ in the extent to which eumelanin and phaeomelanin are present [13]. These melanin-based ornaments are condition dependent in their expression and can be influenced by the social environment [14] and nutritional condition [15], although see also [16], [17].…”

Dispersive Raman spectroscopy allows the identification and quantification of melanin types

“…In addition to the dispersive Raman spectrometer, we used a FT-Raman spectrometer to analyze pheomelanin from feathers (in this case, orange flank feathers from a zebra finch Taenyopigia guttata , as degradative analyses have shown that the color of these feathers is due to the presence of pheomelanin; McGraw and Wakamatsu 2004) and compare the results with those obtained with dispersive Raman. We also analyzed synthetic pheomelanin derived from 5-S-cysteinyldopa (5SCD), the most abundant cysteinyldopa isomer that is formed when cysteine is added to dopaquinone (i.e., the first step of the pheomelanogenesis pathway), synthesized from DOPA (3, 4-dihydroxyphenylalanine) and cysteine using tyrosinase as a natural oxidant following Wakamatsu et al.…”