Butterfly wings often display structural colors, which are the result of light reflection from chitinous nanostructures that adorn the wing scales. Amongst these structural colors are broadband metallic reflections, which have been previously linked to an ultrathin broadband reflector in the nymphalid butterfly Argyrophorus argenteus. To test if similar optical modes of broadband, specular reflectance have evolved in other butterfly taxa, we characterized the reflective scales of eight species from five Papilionoidea families using microspectrophotometry (MSP), light microscopy in reflected and transmitted modes, and scanning electron microscopy (SEM). In Nymphalidae, Pieridae, and Hesperidae, and Lycaenidae, we find that broadband specularity is due to spatial mixing of densely juxtaposed colorful reflectances that change across microscale distances (e.g., 1–3 μm). These seemingly convergent silver scales are unpigmented, show a continuous upper lamina with reduced windows, and consist of an air-cuticle sandwich of variable thickness, forming an undulatory thin-film. Strikingly, Hypochrysops apelles (Lycaenidae) shows a novel mode of silver reflectance with spatial color mixing occurring across the entire proximo-distal length of the scale (>100 μm), transitioning from blue to red hues between the stem and the tip of the scales. Unlike the undulatory type, this reflector shows flat thin-films which also includes a multilayered lower lamina, responsible for selective color iridescence in other lycaenids or in sunset moths. Finally, the gold scales of Anteros formosus (Riodinidae) show mixed reflectance in the green-to-red range, seemingly produced by a thin film in the lower lamina. Our comparative study suggests that evolution of metallic broadband reflectance repeatedly involved spatial color mixing and unperforated upper laminae, and is accomplished using at least three types of ultrastructural modifications. Undulatory thin-film systems, based on geometric adjustments of the transverse profile of the upper lamina and scale lumen, are widespread and may have evolved repeatedly from more generic colorless scale morphologies, while lycaenid and riodinid broadband reflectors may be elaborations of pre-existing iridescent states.

中文翻译：

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宽带反射器的收敛演化是蝴蝶金属着色的基础

蝴蝶翅膀通常显示结构颜色，这是装饰翅膀鳞片的几丁质纳米结构反射光的结果。在这些结构色中，有宽带金属反射，之前已将其与若虫蝴蝶 Argyrophorus argenteus 中的超薄宽带反射器相关联。为了测试类似的宽带光学模式，镜面反射在其他蝴蝶分类群中是否已经进化，我们使用显微分光光度法 (MSP)、反射和透射模式的光学显微镜以及扫描电子显微镜 (SEM) 对来自五个凤蝶科的 8 个物种的反射尺度进行了表征。 ）。在蛱蝶科、粉蝶科、蛱蝶科和狼蛛科中，我们发现宽带镜面反射是由于密集并列的彩色反射率在微尺度距离（例如，1-3 μm）上发生变化的空间混合。这些看似会聚的银鳞没有着色，显示出连续的上层薄板和减少的窗口，并由厚度可变的空气角质层夹层组成，形成起伏的薄膜。引人注目的是，Hypochrysops apelles (Lycaenidae) 显示出一种新的银色反射模式，在整个鳞片近端长度 (>100 μm) 上发生空间颜色混合，在茎和鳞片尖端之间从蓝色过渡到红色. 与波动型不同，这种反射器显示出平坦的薄膜，其中还包括多层下层，负责在其他lycaenids 或日落飞蛾中选择性彩色虹彩。最后，Anteros formosus（Riodinidae）的金鳞在绿色到红色范围内显示混合反射，似乎是由下层的薄膜产生的。我们的比较研究表明，金属宽带反射率的演变反复涉及空间颜色混合和未穿孔的上层，并且至少使用三种类型的超微结构修改来完成。基于上层和鳞片腔的横向轮廓的几何调整的起伏薄膜系统很普遍，并且可能从更通用的无色鳞片形态反复演变而来，而lycaenid和riodinid宽带反射器可能是预先存在的彩虹色状态。我们的比较研究表明，金属宽带反射率的演变反复涉及空间颜色混合和未穿孔的上层，并且至少使用三种类型的超微结构修改来完成。基于上层和鳞片腔的横向轮廓的几何调整的起伏薄膜系统很普遍，并且可能从更通用的无色鳞片形态反复演变而来，而lycaenid和riodinid宽带反射器可能是预先存在的彩虹色状态。我们的比较研究表明，金属宽带反射率的演变反复涉及空间颜色混合和未穿孔的上层，并且至少使用三种类型的超微结构修改来完成。基于上层和鳞片腔的横向轮廓的几何调整的起伏薄膜系统很普遍，并且可能从更通用的无色鳞片形态反复演变而来，而lycaenid和riodinid宽带反射器可能是预先存在的彩虹色状态。