Polarized iridescence of the multilayered elytra of the Japanese jewel beetle,<i>Chrysochroa fulgidissima</i>

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

doi:10.1098/rstb.2010.0197

Cited by 144 publications

(160 citation statements)

References 27 publications

(47 reference statements)

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“…14 The two barbule lanes of Figure 4a yielded for normal illumination the spectra shown in Figure 4b. The calculated reflectance spectra always peaked in the infrared and furthermore showed clear oscillations in the far-red wavelength range (Figure 3a).…”

Section: Multilayer Modelingmentioning

confidence: 99%

“…Scaling the local density accordingly yielded the local refractive index along each lane. We implemented these values in a matrix-based optical multilayer program, 14 which for each of the 36 lanes produced the wavelength-dependent reflectance, R, and transmittance, T, as a function of incident angle and polarization. The average of the 36 reflectance spectra was taken to represent the barbule reflectance spectrum.…”

Section: Microspectrophotometrymentioning

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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Section: Multilayer Modelingmentioning

confidence: 99%

Section: Microspectrophotometrymentioning

confidence: 99%

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

et al. 2015

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“…The wing scales were embedded in a mixture of Epon and Araldite following a standard embedding procedure [12].…”

Section: (D) Anatomymentioning

confidence: 99%

Brilliant camouflage : photonic crystals in the diamond weevil, Entimus imperialis

et al. 2012

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The neotropical diamond weevil, Entimus imperialis, is marked by rows of brilliant spots on the overall black elytra. The spots are concave pits with intricate patterns of structural-coloured scales, consisting of large domains of three-dimensional photonic crystals that have a diamond-type structure. Reflectance spectra measured from individual scale domains perfectly match model spectra, calculated with anatomical data and finite-difference time-domain methods. The reflections of single domains are extremely directional (observed with a point source less than 58), but the special arrangement of the scales in the concave pits significantly broadens the angular distribution of the reflections. The resulting virtually angle-independent green coloration of the weevil closely approximates the colour of a foliaceous background. While the closedistance colourful shininess of E. imperialis may facilitate intersexual recognition, the diffuse green reflectance of the elytra when seen at long-distance provides cryptic camouflage.

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“…Third, the layers of light and dark materials in the cuticle act as multi-layer reflectors that produce colour through thin-film interference. Finally, the low estimated contrast in RI between these layers explains why the observed large number of repeating layers does not produce bright colours, as similar structures do in other cases [1,10]. Typical non-iridescent hairs are circular to ovoid in cross section and have large and protruding cuticular scales ( figure 1; electronic supplementary material, figure S2), but may have multi-layered cuticles [11].…”

Section: Discussionmentioning

confidence: 99%

“…However, because the material constituting the dark layers and the extinction coefficient (k; a measure of how much light a material absorbs) of hair keratin is unknown, several parameters of the model (RI of dark material; k of dark and light materials) were allowed to vary under an optimization procedure (see electronic supplementary material). Optimization was performed by minimizing the sum of squared differences between normalized values of measured and estimated reflectance at each wavelength (modified from Stavenga et al [10]). We compared measured and predicted reflectance curves to determine the accuracy of modelling.…”

Section: Methodsmentioning

confidence: 99%

Iridescent colour production in hairs of blind golden moles ( Chrysochloridae )

et al. 2012

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Relative to other metazoans, the mammalian integument is thought to be limited in colour. In particular, while iridescence is widespread among birds and arthropods, it has only rarely been reported in mammals. Here, we examine the colour, morphology and optical mechanisms in hairs from four species of golden mole (Mammalia: Chrysochloridae) that are characterized by sheens ranging from purple to green. Microspectrophotometry reveals that this colour is weak and variable. Iridescent hairs are flattened and have highly reduced cuticular scales, providing a broad and smooth surface for light reflection. These scales form multiple layers of light and dark materials of consistent thickness, strikingly similar to those in the elytra of iridescent beetles. Optical modelling suggests that the multi-layers produce colour through thin-film interference, and that the sensitivity of this mechanism to slight changes in layer thickness and number explains colour variability. While coloured integumentary structures are typically thought to evolve as sexual ornaments, the blindness of golden moles suggests that the colour may be an epiphenomenon resulting from evolution via other selective factors, including the ability to move and keep clean in dirt and sand.

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Polarized iridescence of the multilayered elytra of the Japanese jewel beetle,Chrysochroa fulgidissima

Cited by 144 publications

References 27 publications

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

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

Brilliant camouflage : photonic crystals in the diamond weevil, Entimus imperialis

Iridescent colour production in hairs of blind golden moles ( Chrysochloridae )

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