Rapid and reversible humidity-dependent colour change by water film formation in a scaled springtail: Image compilations and video recordings

Colour is often not a static trait but can change over time either through biotic or abiotic factors.  Humidity-dependent colour change can occur through either morphological change (e.g. to feather barbules in birds) or by the replacement of air by water causing a shift in refractive index, as seen in arthropod multilayer cuticles or scales. The scaled springtail Lepidocyrtus cyaneus has scales that produce color largely via thin film interference from their lamina. We observed a marked colour change from golden to violet/purple colouration in humid conditions. Light microscopy, microspectrophotometry, contact angle goniometry and optical modelling indicate that the formation of a thin film of water on top of the hydrophilic scales increases their laminar thin film thickness, causing a shift towards violet/purple colour. Evaporation of the water film causes the metallic golden colour to return. This constitutes a remarkably rapid colour change (in the order of seconds), only limited by...

色彩往往并非静态性状，而是可随时间推移因生物或非生物因素发生改变。依赖湿度的色彩变化可通过两种途径产生：一是形态学改变（如鸟类的羽小枝），二是空气被水取代导致折射率（refractive index）变化，这一现象可见于节肢动物的多层角质层或鳞片结构中。鳞跳虫（scaled springtail）*Lepidocyrtus cyaneus*的鳞片主要通过其薄板结构的薄膜干涉（thin film interference）产生色彩。本研究观察到，在高湿度条件下，该物种会出现显著的色彩转变：从金属金色变为蓝紫色/紫色。光学显微镜术（light microscopy）、显微分光光度法（microspectrophotometry）、接触角测角仪（contact angle goniometry）分析与光学建模（optical modelling）结果表明：亲水鳞片表面形成的超薄水膜会增厚其层状薄膜厚度，进而使色彩向蓝紫色/紫色偏移。水膜蒸发后，其金属金色的体色便可恢复。这是一种极为快速的色彩变化（耗时仅为数秒量级），其速率仅受限于……