Data from: The evolution of feather coloration and song in Old World orioles (genus Oriolus)

What is the tempo and mode of evolution – how fast and in what pattern do traits evolve – is a major question of evolutionary biology. Here we studied patterns of evolutionary change in visual and acoustic signals in Old World orioles. Since producing multiple signals may be costly, we also tested whether there was an evolutionary trade-off between the elaboration of those two types of signals. We studied 30 Oriolus taxa using comparative methods and a recent molecular phylogeny. Morphology and plumage hue evolved comparatively slowly, whereas song evolved rapidly. Among individual feather patches, the evolutionary rate of color was slowest in primaries, which are critical for flapping flight, and fastest in patches exposed to observers (mantle and breast). Thus, primaries seem to be under functional constraint while the evolution of visually exposed patches is perhaps shaped by sexual selection. Song evolution was comparatively fast, but also attracted to a single optimum. This may be due to selection for signal efficacy, because all orioles inhabit similar forested habitats. Only color diversity was best fit by a speciational model: the biggest changes in coloration were concentrated at speciation events, thus perhaps linked to the evolution of species recognition. Our analysis did not reveal any evolutionary trade-off between acoustic and visual signals, suggesting that the elaboration of visual and acoustic signals in the Old World orioles evolved independently. Our study shows that patterns of evolutionary change may be surprisingly complex even within a single clade of birds and thus further studies are needed to identify general patterns of signal macroevolution.

演化的速率与模式——即性状演化的快慢与具体形式为何——是进化生物学（evolutionary biology）的核心研究议题之一。本研究针对旧世界黄鹂（Old World orioles）类群的视觉与声学信号演化变化模式展开分析。鉴于多信号产生可能存在能量成本，本研究同时检验了这两类信号的精细化演化之间是否存在进化权衡（evolutionary trade-off）。本研究采用比较方法（comparative methods）与最新的分子系统发育（molecular phylogeny）数据，对30个黄鹂属（Oriolus）类群开展了分析。形态与羽色色调的演化速率相对缓慢，而鸣唱信号的演化则较为迅速。在单个羽毛区域中，初级飞羽（primaries）的颜色演化速率最慢——该结构对振翅飞行至关重要，而暴露于观察者视野的区域（如背部与胸部）的颜色演化速率最快。由此可见，初级飞羽似乎受到功能约束，而暴露于视野的羽毛区域的演化则可能受到性选择（sexual selection）的塑造。鸣唱信号的演化速率虽快，却收敛于单一最优表型。这一现象可能源于信号效率的选择压力——所有黄鹂类群均栖息于相似的森林生境中。唯有颜色多样性的演化最符合物种形成模型（speciational model）：体色的最大变化集中于物种形成事件期间，因此可能与物种识别（species recognition）的演化相关。本研究未发现声学与视觉信号之间存在进化权衡，表明旧世界黄鹂的视觉与声学信号精细化演化过程彼此独立。本研究表明，即便在单一鸟类支系（clade）内，演化变化模式也可能出人意料地复杂，因此仍需开展更多研究以揭示信号宏观演化（macroevolution）的通用模式。