Data from: Evolution of long-term coloration trends with biochemically unstable ingredients

The evolutionarily persistent and widespread use of carotenoid pigments in animal coloration contrasts with their biochemical instability. Consequently, evolution of carotenoid-based displays should include mechanisms to accommodate or limit pigment degradation. In birds, this could involve two strategies: 1) evolution of a molt immediately prior to the mating season, enabling the use of particularly fast-degrading carotenoids, and 2) evolution of the ability to stabilize dietary carotenoids through metabolic modification or association with feather keratins. Here we examine evolutionary lability and transitions between the two strategies across 126 species of birds. We report that species that express mostly unmodified, fast-degrading, carotenoids have pre-breeding molts, and a particularly short time between carotenoid deposition and the subsequent breeding season. Species that expressed mostly slow-degrading carotenoids in their plumage accomplished this through increased metabolic modification of dietary carotenoids, and the selective expression of these slow-degrading compounds. In these species, the timing of molt was not associated with carotenoid composition of plumage displays. Using repeated samples from individuals of one species, we found that metabolic modification of dietary carotenoids significantly slowed their degradation between molt and breeding season. Thus, the most complex and colorful ornamentation is likely the most biochemically stable in birds, and depends less on ecological factors, such as molt timing and migration tendency. We suggest that coevolution of metabolic modification, selective expression, and biochemical stability of plumage carotenoids enables the use of unstable pigments in long-term evolutionary trends in plumage coloration.

类胡萝卜素色素（carotenoid pigments）在动物体色演化中持续且广泛的分布，与其生化不稳定性形成鲜明反差。因此，基于类胡萝卜素的体色展示的演化过程，必然包含应对或限制色素降解的相关机制。
在鸟类中，这一过程可归纳为两种策略：1）演化出繁殖季前的换羽行为，从而得以使用降解速度极快的类胡萝卜素；2）演化出通过代谢修饰或与羽毛角蛋白（feather keratins）结合，来稳定膳食类胡萝卜素（dietary carotenoids）的能力。
本研究针对126种鸟类，分析了这两种策略间的进化易变性（evolutionary lability）以及演化过渡事件。研究结果显示：主要表达未修饰、降解快速的类胡萝卜素的鸟类，均具备繁殖前换羽行为，且类胡萝卜素沉积至后续繁殖季的时间间隔极短。
而羽饰中主要表达降解缓慢的类胡萝卜素的鸟类，则通过增强对膳食类胡萝卜素的代谢修饰，以及选择性表达这类降解缓慢的化合物来实现这一特征。在这类鸟类中，换羽时机与羽饰类胡萝卜素组成并无显著关联。
通过对单一物种种群个体的重复采样，我们发现：对膳食类胡萝卜素的代谢修饰，可显著延缓换羽至繁殖季期间的色素降解过程。
由此可见，鸟类中结构最复杂、色彩最艳丽的羽饰，往往生化稳定性也最强，且较少依赖换羽时机、迁徙倾向等生态因子。我们认为，羽饰类胡萝卜素的代谢修饰、选择性表达与生化稳定性的协同演化，使得不稳定色素能够被应用于羽色演化的长期趋势之中。