Quantifying the refractive index dispersion of a pigmented biological tissue using Jamin–Lebedeff interference microscopy

Stavenga, Doekele G.; Leertouwer, Hein L.; Wilts, Bodo D.

doi:10.1038/lsa.2013.56

Cited by 53 publications

(51 citation statements)

References 28 publications

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“…The measured absorbance spectra of our various scale types (Fig. 3D) do not match the melanin absorbance spectrum exactly (30,32,33), indicating that brown scales in B. anynana either do not contain melanin or, more likely, contain additional pigments besides melanin. Because the type and amount of pigments that exist in the lower lamina of scales are not known, we cannot accurately estimate the change of refractive index value caused by pigmentation.…”

Section: Resultsmentioning

confidence: 99%

Artificial selection for structural color on butterfly wings and comparison with natural evolution

Wasik

Liew

Lilien

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Brilliant animal colors often are produced from light interacting with intricate nano-morphologies present in biological materials such as butterfly wing scales. Surveys across widely divergent butterfly species have identified multiple mechanisms of structural color production; however, little is known about how these colors evolved. Here, we examine how closely related species and populations of Bicyclus butterflies have evolved violet structural color from brown-pigmented ancestors with UV structural color. We used artificial selection on a laboratory model butterfly, B. anynana, to evolve violet scales from UV brown scales and compared the mechanism of violet color production with that of two other Bicyclus species, Bicyclus sambulos and Bicyclus medontias, which have evolved violet/blue scales independently via natural selection. The UV reflectance peak of B. anynana brown scales shifted to violet over six generations of artificial selection (i.e., in less than 1 y) as the result of an increase in the thickness of the lower lamina in ground scales. Similar scale structures and the same mechanism for producing violet/blue structural colors were found in the other Bicyclus species. This work shows that populations harbor large amounts of standing genetic variation that can lead to rapid evolution of scales' structural color via slight modifications to the scales' physical dimensions.thin film | constructive interference | parallel evolution | photonics O rganisms produce colors in two basic ways: by synthesizing pigments that selectively absorb light of certain spectral bands so that only light outside the absorption bands is backscattered (chemical color) or by developing nanomorphologies that enhance the reflection of light of certain wavelengths by interference (physical color or structural color). Structural colors play major roles in natural and sexual selection in many species (1) and have a broad range of applications in color display, paint, cosmetics, and textile industries (2). Structural color surveys across widely divergent species have revealed a large diversity of color-producing mechanisms (3-9). However, there has been a lack of systematic study and comparison of how different colors from closely related species or within populations of a single species evolve, even though these colors can vary dramatically. By examining how these species/populations evolve different colors, it is possible to identify the minimal amount of morphological change that results in significant color variation. Furthermore, this research may serve as an inspiration for future application of similar evolutionary principles to the design of photonic devices for color tuning, light trapping, or beam steering (2,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). From an evolutionary biology point of view, we are curious to examine how structural colors respond to selection pressure and whether there is sufficient standing genetic variation in natural populations to allow the rapid evolution of novel colors. Here we focus on d...

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Section: Resultsmentioning

confidence: 99%

Artificial selection for structural color on butterfly wings and comparison with natural evolution

Wasik

Liew

Lilien

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The refractive index is modified by high pigment concentrations (e.g. Stavenga et al, 2013), and therefore we also calculated the reflectance spectrum of a 200 nm thick scale containing the pigment measured in the blue scale of Fig. 3B; this yielded a virtually identical spectrum as that for the unpigmented scale (not shown).…”

Section: Thin Filmsmentioning

confidence: 99%

Colouration principles of nymphaline butterflies - thin films, melanin, ommochromes and wing scale stacking

Stavenga

Leertouwer

Wilts

2014

Journal of Experimental Biology

141

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The coloration of the common butterflies Aglais urticae (small tortoiseshell), Aglais io (peacock) and Vanessa atalanta (red admiral), belonging to the butterfly subfamily Nymphalinae, is due to the species-specific patterning of differently coloured scales on their wings. We investigated the scales' structural and pigmentary properties by applying scanning electron microscopy, (micro)spectrophotometry and imaging scatterometry. The anatomy of the wing scales appears to be basically identical, with an approximately flat lower lamina connected by trabeculae to a highly structured upper lamina, which consists of an array of longitudinal, parallel ridges and transversal crossribs. Isolated scales observed at the abwing (upper) side are blue, yellow, orange, red, brown or black, depending on their pigmentation. The yellow, orange and red scales contain various amounts of 3-OH-kynurenine and ommochrome pigment, black scales contain a high density of melanin, and blue scales have a minor amount of melanin pigment. Observing the scales from their adwing (lower) side always revealed a structural colour, which is blue in the case of blue, red and black scales, but orange for orange scales. The structural colours are created by the lower lamina, which acts as an optical thin film. Its reflectance spectrum, crucially determined by the lamina thickness, appears to be well tuned to the scales' pigmentary spectrum. The colours observed locally on the wing are also due to the degree of scale stacking. Thin films, tuned pigments and combinations of stacked scales together determine the wing coloration of nymphaline butterflies.

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“…For a quantitative understanding of the measured reflectance and transmittance spectra, the refractive index of the constituent layers has to be known. We first determined the refractive index as a function of wavelength of both the main barbule area and the cell center by applying Jamin-Lebedeff interference microscopy 12 Melanin refractive index of bird feathers DG Stavenga et al The refractive index of melanin in feathers has been a matter of conjecture for several decades. For the pigeon Columba trocaz, whose barbule cells contain melanin granules and air spaces in a keratin matrix, application of a series of immersion fluids led Schmidt 1 to conclude that the granule refractive index exceeds 1.739 (n D of methylene iodide), that it approximates 1.76-1.77 (ruby and sapphire) and is less than 2.42 (diamond).…”

Section: Barbule and Melanin Refractive Indexmentioning

confidence: 99%

“…12 Briefly, we mounted small sections of isolated barbules, immersed in various refractive index fluids (Cargille Labs, Cedar Grove, NJ, USA), on the stage of the Zeiss Universal Microscope set-up for Jamin-Lebedeff interference microscopy, and we thus obtained the mean refractive index of the occipital feather barbules as a function of wavelength, n b (l); for examples and detailed explanation, see Supplementary Information. Subsequently, we used transmission electron micrographs to determine the contribution of melanin to the refractive index.…”

Section: Microspectrophotometrymentioning

confidence: 99%

“…Additionally, we determined the barbule refractive index by interference microscopy. [11][12][13] From the barbule anatomy, we assessed the contribution of melanin to the barbule refractive index and could thus determine the refractive index of melanin as a function of wavelength. By implementing the accumulated data in an optical multilayer model, we could closely reproduce measured angledependent reflectance spectra.…”

Section: Introductionmentioning

confidence: 99%

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High refractive index of melanin in shiny occipital feathers of a bird of paradise

et al. 2015

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Male Lawes's Parotia, a bird of paradise, use the highly directional reflection of the structurally colored, brilliant-silvery occipital feathers in their courtship display. As in other birds, the structural coloration is produced by ordered melanin pigmentation. The barbules of the Parotia's occipital feathers, with thickness ,3 mm, contain 6-7 layers of densely packed melanin rodlets (diameter ,0.25 mm, length ,2 mm). The effectively ,0.2 mm thick melanin layers separated by ,0.2 mm thick keratin layers create a multilayer interference reflector. Reflectance measurements yielded peak wavelengths in the near-infrared at ,1.3 mm, i.e., far outside the visible wavelength range. With the Jamin-Lebedeff interference microscopy method recently developed for pigmented media, we here determined the refractive index of the intact barbules. We thus derived the wavelength dependence of the refractive index of the barbules' melanin to be 1.7-1.8 in the visible wavelength range. Implementing the anatomical and refractive index data in an optical multilayer model, we calculated the barbules' reflectance, transmittance and absorptance spectra, thereby confirming measured spectra. Keywords: bird of paradise; interference reflector; iridescence; Jamin-Lebedeff microscopy; multilayer INTRODUCTIONIn animal integuments melanins commonly produce dull red, brown and black colors. With nanoscale order, melanin in a matrix of vertebrate keratin or arthropod chitin can produce striking structural colors. [1][2][3][4] The magnificent displays of birds of paradise exemplify how the fine branches of the bird feathers, the barbules, are modified to achieve a diverse range of visual effects through structural coloration. In Lawes's Parotia (Parotia lawesii), the barbules of the males' breast feathers have a boomerang-shaped cross-section, which produces three directional-colored reflectors. 5 Here we investigate the male Parotia's occipital (or nape) feathers, which produce a shiny, silvery patch (Figure 1a and 1b). Compared to the breast feathers they are less colorful, but the barbules of the occipital feathers exhibit a mirror-like, directional reflection due to nanostructured melanin. 6 The uniquely colorful breast feathers allows the breast color to switch sharply between yellow, blue and black as the bird moves, during the ballerina dance, which is performed as part of the courtship display. [7][8][9] The shiny occipital feathers have a similar function. Recent behavioral observations on the closely related Wahnes's Parotia demonstrate that the occipital feather reflections are sharply directed to the observing females during part of the courtship performance, presumably to impress a potential mate, viewing from an elevated position on a tree branch. [6][7][8][9][10] To unravel the optical basis of the shiny occipital reflectors, we investigated the barbule anatomy. This revealed very regularly arranged melanosomes, i.e., small melanin rodlets, arranged in layers. To achieve an in-depth, quantitative understanding of the feathers'

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Quantifying the refractive index dispersion of a pigmented biological tissue using Jamin–Lebedeff interference microscopy

Cited by 53 publications

References 28 publications

Artificial selection for structural color on butterfly wings and comparison with natural evolution

Artificial selection for structural color on butterfly wings and comparison with natural evolution

Colouration principles of nymphaline butterflies - thin films, melanin, ommochromes and wing scale stacking

High refractive index of melanin in shiny occipital feathers of a bird of paradise

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