Relative contributions of pigments and biophotonic nanostructures to natural color production: a case study in budgerigar (Melopsittacus undulatus) feathers

Abstract

SUMMARYUnderstanding the mechanistic bases of natural color diversity can provide insight into its evolution and inspiration for biomimetic optical structures. Metazoans can be colored by absorption of light from pigments or by scattering of light from biophotonic nanostructures, and these mechanisms have largely been treated as distinct. However, the interactions between them have rarely been examined. Captive breeding of budgerigars (Aves, Psittacidae, Melopsittacus undulatus) has produced a wide variety of color morphs spanning the majority of the spectrum visible to birds, including the ultraviolet, and thus they have been used as examples of hypothesized structure-pigment interactions. However, empirical data testing these interactions in this excellent model system are lacking. Here we used ultraviolet-visible spectrometry, light and electron microscopy, pigment extraction experiments and optical modeling to examine the physical bases of color production in seven budgerigar morphs, including grey and chromatic (purple to yellow) colors. Feathers from all morphs contained quasi-ordered air-keratin ʻspongy layerʼ matrices, but these were highly reduced and irregular in grey and yellow feathers. Similarly, all feathers but yellow and grey had a layer of melanin-containing melanosomes basal to the spongy layer. The presence of melanosomes likely increases color saturation produced by spongy layers whereas their absence may allow increased expression of yellow colors. Finally, extraction of yellow pigments caused some degree of color change in all feathers except purple and grey, suggesting that their presence and contribution to color production is more widespread than previously thought. These data illustrate how interactions between structures and pigments can increase the range of colors attainable in birds and potentially in synthetic systems. Supplementary material available online at

Functional optics of glossy buttercup flowers

“…[14,39]) and birds (e.g. [40]), but is very rare among flowers. In flowers of the vast majority of plant species, specular reflections are absent, because of the presence of conical epidermal cells and/or epidermal microstructures [5,20] that scatter light into a wide angular space [19].…”

Spectral tuning of Amazon parrot feather coloration by psittacofulvin pigments and spongy structures

“…5A, green curve). Its greenpeaking reflectance is due to a blue-green, broad-band reflecting spongy structure filtered by a short-wavelength-absorbing, yellow pigment (D'Alba et al, 2012;Saranathan et al, 2012). In both the blue and dark-green reflecting areas the barbules are black, because of melanin pigmentation.…”

“…The green feathers also have spongy cells, which reflect blue-green light. A blue-absorbing pigment, which functions as a short-wavelength filter, restricts the wavelength range of the reflected light, resulting in green coloured feathers (Berg and Bennett, 2010;D'Alba et al, 2012;Saranathan et al, 2012).…”

Structural Color in Marine Algae

“…Such nanostructures, with features on the mesoscale (i.e., ≈100 nm), are capable of producing vivid, saturated colors through interference. [ 1 ] Different organisms exploit a variety of nanostructures and materials which, often combined with underlying pigmentation, can produce a wide range of complex optical effects, [ 2,3 ] ranging from metallic and iridescent colors [ 4,5 ] to bright whites. [ 6 ] In nature, structural color occurs in the marine and terrestrial environments in organisms across the tree of life, including birds, [7][8][9] insects, [10][11][12][13][14] land plants [ 15,16 ] (e.g., in the leaves, [ 17,18 ] fl owers [19][20][21] and fruit [ 22,23 ] ), bacteria, [ 24 ] fungi, [ 25 ] slime molds, [ 26 ] viruses, [ 27 ] diatoms [ 28 ] and macroalgae.…”