Data from: Modular color evolution facilitated by a complex nanostructure in birds

The way in which a complex trait varies, and thus evolves, is critically affected by the independence, or modularity, of its subunits. How modular designs facilitate phenotypic diversification is well studied in non-ornamental (e.g., cichlid jaws), but not ornamental traits. Diverse feather colors in birds are produced by light absorption by pigments and/or light scattering by nanostructures. Such structural colors are deterministically related to the nanostructures that produce them and are therefore excellent systems to study modularity and diversity of ornamental traits. Elucidating if and how these nanostructures facilitate color diversity relies on understanding how nanostructural traits covary, and how these traits map to color. Both of these remain unknown in an evolutionary context. Most dabbling ducks (Anatidae) have a conspicuous wing patch with iridescent color caused by a two-dimensional photonic crystal of small (100–200 nm) melanosomes. Here, we ask how this complex nanostructure affects modularity of color attributes. Using a combination of electron microscopy, spectrophotometry, and comparative methods, we show that nanostructural complexity causes functional decoupling and enables independent evolution of different color traits. These results demonstrate that color diversity is facilitated by how nanostructures function and may explain why some birds are more color-diverse than others.复杂性状的变异与演化路径，关键取决于其亚基的独立性，即模块化性（modularity）。模块化设计如何推动表型多样性，在非装饰性性状（non-ornamental traits，例如慈鲷的颌骨）中已有充分研究，但针对装饰性性状（ornamental traits）的相关探讨仍较为匮乏。鸟类多样的羽色由色素的光吸收作用与纳米结构的光散射共同产生。这类结构色（structural colors）与生成它们的纳米结构存在确定性关联，因此是研究装饰性性状模块化性与多样性的理想模型体系。要阐明这些纳米结构是否以及如何促进色彩多样性，需先明确纳米结构性状间的协同变异规律，以及这些性状如何映射为色彩；而在演化框架下，这两个核心问题均尚未得到解答。多数钻水鸭（dabbling ducks）隶属于鸭科（Anatidae），其拥有醒目的翼斑，该翼斑的虹彩色泽由直径100~200纳米的黑色素体（melanosomes）构成的二维光子晶体（photonic crystal）所产生。本研究旨在探究这类复杂纳米结构如何影响色彩性状的模块化性。本研究结合电子显微镜（electron microscopy）、分光光度法（spectrophotometry）与比较演化方法（comparative methods），证明纳米结构的复杂性会造成功能解耦，使得不同色彩性状得以独立演化。本研究结果表明，纳米结构的功能特性推动了色彩多样性的形成，这或可解释为何部分鸟类的羽色多样性显著高于其他类群。