Complex plumages spur rapid color diversification in kingfishers (Aves: Alcedinidae)

Colorful signals in nature provide some of the most stunning examples of rapid phenotypic evolution. Yet, studying color pattern evolution has been historically difficult owing to differences in perceptual ability of humans and analytical challenges with studying how complex color patterns evolve. Island systems can provide a natural laboratory for testing hypotheses about the direction and magnitude (i.e., rate) of phenotypic change. A recent study of bird coloration found that the plumages of island species are darker and less complex than continental species. Whether such shifts in plumage complexity are associated with increased rates of color evolution on islands remains unknown. Here, we use geometric morphometric techniques to test the hypothesis that plumage complexity and island insularity interact to influence color diversity in a species-rich and cosmopolitan clade of colorful birds—kingfishers (Aves: Alcedinidae). In particular, we test three predictions: i) plumage complexity enhances interspecific rates of color evolution, ii) plumage complexity is lower on islands, and iii) rates of plumage color evolution are higher within island systems. Our results show that more complex plumages result in more diverse colors among species and that island species have higher rates of color evolution. Importantly, we found that island species did not have more complex plumages than their continental relatives. Thus, complexity may be a key innovation that facilitates response to relaxed (or divergent) selection pressures on islands. Lack of strong support for competition-driving rates of evolution along different color axes hints at an allopatric model of color evolution in which species adapt to local conditions on different islands. This study demonstrates how a truly multivariate treatment of color data can reveal evolutionary patterns that might otherwise go unnoticed.

Methods
This data was collected with a UV-Vis spectrophotometer.

自然界中的色彩信号是快速表型演化最引人注目的例证之一。然而，受限于人类感知能力的局限性，以及解析复杂色彩图案演化机制所面临的分析难题，长期以来色彩图案演化的研究颇具挑战。岛屿生态系统可作为天然实验室，用于检验表型演化方向与强度（即演化速率）相关的科学假说。
近期一项针对鸟类体色的研究发现，岛屿物种的羽色较大陆物种更深，且复杂程度更低。但这类羽色复杂度的变化是否与岛屿上色彩演化速率的提升存在关联，目前仍不明朗。
本研究采用几何形态测量技术，针对物种丰富且广布的色彩丰富鸟类演化支——翠鸟（鸟纲：翠鸟科），检验了“羽色复杂度与岛屿隔离性共同影响色彩多样性”的假说。具体而言，我们验证了三项预测：其一，羽色复杂度会提升物种间的色彩演化速率；其二，岛屿物种的羽色复杂度更低；其三，岛屿生境中的羽色色彩演化速率更高。
研究结果显示，羽色越复杂，物种间的色彩多样性越高，且岛屿物种的色彩演化速率更快。值得注意的是，本研究未发现岛屿物种的羽色复杂度高于其大陆近缘类群的证据。由此可见，羽色复杂度或许是助力岛屿上放松（或趋异）选择压力下适应性演化的关键创新。我们未发现强烈证据支持竞争驱动不同色彩维度上的演化速率，这暗示了色彩演化的异域分化模型：即不同岛屿上的物种各自适应当地环境条件。本研究证实，对色彩数据开展真正的多变量分析，能够揭示此前可能被忽略的演化模式。
方法
本数据集通过紫外-可见分光光度计（UV-Vis spectrophotometer）采集获得。