Department of Physics, Kookmin University, Seoul, South Korea.
Smart Natural Space Research Centre, Kongju National University, Cheonan, South Korea.
PLoS One. 2023 Mar 22;18(3):e0282053. doi: 10.1371/journal.pone.0282053. eCollection 2023.
The tail feathers of magpies are iridescent, with hues ranging from navy to violet and green. It has been previously shown that the hexagonal arrangement of melanosomes in the distal barbules is responsible for these colors, but previous simulation models have relied on average values for the parameters associated with this arrangement (e.g., periodicity), and it remains to be studied whether the actual (rather than averaged) structural arrangement and its inherent irregularities reliably predict structural color. Previous studies using unmodified images for the analysis have not focused on the effect of such irregularities on the color production. In this study, we conducted finite-difference time-domain (FDTD) simulations using actual transmission electron microscopy (TEM) images obtained from the distal barbules of a magpie tail feather, compared the reflectance spectra predicted using the FDTD simulation with those measured with a spectrometer, and found a substantial discrepancy between the two. Fourier analysis suggests that the non-uniform arrangement of the melanosomes within the barbule is responsible for this discrepancy by creating variation in the periodicity. Our results suggest that a simple model in which the parameters for internal structures are averaged cannot fully explain the variation in the structural colors observed in biological samples such as the feathers of birds.
喜鹊的尾羽呈现出虹彩色，色调范围从海军蓝到紫色和绿色。先前已经表明，远端羽小枝中黑素体的六边形排列是产生这些颜色的原因，但以前的模拟模型依赖于与这种排列相关的参数的平均值（例如，周期性），并且仍然需要研究实际（而不是平均）结构排列及其固有不规则性是否可靠地预测结构颜色。以前使用未经修改的图像进行分析的研究并未关注这些不规则性对颜色产生的影响。在这项研究中，我们使用从喜鹊尾羽的远端羽小枝获得的实际透射电子显微镜 (TEM) 图像进行了有限差分时域 (FDTD) 模拟，比较了 FDTD 模拟预测的反射率光谱与光谱仪测量的反射率光谱，并发现两者之间存在很大差异。傅里叶分析表明，羽小枝内黑素体的不均匀排列通过在周期性上产生变化，导致了这种差异。我们的结果表明，在内部结构参数平均值的简单模型不能完全解释在生物样本（如鸟类的羽毛）中观察到的结构颜色变化。
