Stavenga Doekele G, van der Kooi Casper J, Wilts Bodo D
Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland.
J R Soc Interface. 2017 Aug;14(133). doi: 10.1098/rsif.2017.0407.
The blue colours of the speculum of the mallard (), both male and female, and the green head feathers of the male arise from light interacting with stacks of melanosomes residing in the feather barbules. Here, we show that the iridescent colours can be quantitatively explained with an optical multilayer model by using a position-dependent effective refractive index, which results from the varying ratio of melanin and keratin. Reflectance spectra obtained by multilayer modelling and three-dimensional finite-difference time-domain calculations were virtually identical. The spectral properties of the barbules' photonic structures are sensitive to variations in the multilayer period and the cortex thickness, but they are surprisingly robust to variations in the spatial parameters of the barbules' melanosome stacks. The blue and green reflectance spectra of the structural-coloured feathers correspond with the sensitivity spectra of the short- and middle-wavelength-sensitive photoreceptors, indicating their biological significance for intraspecific signalling.
绿头鸭（无论雄性还是雌性）镜羽的蓝色以及雄性绿头鸭头部的绿色羽毛，是由光线与位于羽小枝中的黑素体堆叠结构相互作用产生的。在此，我们表明，通过使用位置依赖的有效折射率，利用光学多层模型可以定量解释这些虹彩颜色，该有效折射率由黑色素和角蛋白的比例变化产生。通过多层建模和三维有限差分时域计算获得的反射光谱几乎完全相同。羽小枝光子结构的光谱特性对多层周期和皮质厚度的变化敏感，但令人惊讶的是，它们对羽小枝黑素体堆叠结构的空间参数变化具有很强的鲁棒性。结构色羽毛的蓝色和绿色反射光谱与短波长和中波长敏感光感受器的敏感光谱相对应，表明它们在种内信号传递中具有生物学意义。
