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: (i) evolution of a moult immediately prior to the mating season, enabling the use of particularly fast-degrading carotenoids and (ii) 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 moults, 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 moult 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 moult and breeding season. Thus, the most complex and colourful ornamentation is likely the most biochemically stable in birds, and depends less on ecological factors, such as moult 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久且广泛的使用，与其生化不稳定性形成鲜明对比。因此，基于类胡萝卜素的羽饰展示的演化，应当包含适应或限制色素降解的机制。在鸟类中，这可能涉及两种策略：（i）演化出繁殖季前即刻换羽（moult）的行为，从而得以使用极易快速降解的类胡萝卜素；（ii）演化出通过代谢修饰（metabolic modification）或与羽毛角蛋白（feather keratins）结合来稳定膳食来源类胡萝卜素的能力。本研究针对126种鸟类，探究了这两种策略间的进化可塑性（evolutionary lability）与演化转变。结果显示，主要表达未修饰、易快速降解类胡萝卜素的物种，均具有繁殖前换羽行为，且类胡萝卜素沉积与后续繁殖季之间的间隔极短。而主要在羽饰（plumage）中表达缓慢降解类胡萝卜素的物种，则通过对膳食类胡萝卜素的增强代谢修饰，以及对这类缓慢降解化合物的选择性表达（selective expression）来达成这一目标。在这些物种中，换羽时间与羽饰的类胡萝卜素组成并无关联。通过对某一物种个体的重复采样，我们发现，膳食类胡萝卜素的代谢修饰显著延缓了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、色彩最艳丽的装饰性羽饰，其生化稳定性往往也最高，且较少依赖换羽时间、迁徙倾向等生态因素。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（coevolution），使得在羽色演化的长期趋势中，不稳定色素的使用成为可能。