Reed warblers in the Marquesas Islands: song divergence and plumage convergence of two distinct lineages

The Pacific Ocean is the site of the most important diversification of insular reed warblers (Acrocephalus). In the Marquesas Islands (Eastern Polynesia), reed warblers belong to two distinct lineages that have reached the archipelago independently. We used mitochondrial sequences and microsatellite markers and found evidence of gene flow between the two lineages. One island in particular, Nuku Hiva, seems to act as the main contact zone between the two taxa. We then used reflectance spectrometry to evaluate the variation of carotenoid colouration among all populations. Marquesan reed warblers exhibit convergent evolution in carotenoid-based plumage colouration, but variation among islands was important. Having two different phylogenetic origins, the two lineages acquired their yellow colour independently and there is stochastic variation in plumage among islands. Finally, we analysed the songs of reed warblers from the main islands. Multifactorial analysis showed that vocalisations of Marquesan reed warblers differ slightly between species, significant differences between islands leading to different dialects. Vocal characteristics may act as the main pre-zygotic barriers when birds from different lineages come into contact. This study provides another example of convergence in plumage evolution in insular bird species. Furthermore, it highlights the importance of integrative analyses, using both genetic and phenotypical characters, for the study of the evolutionary history of the Pacific Ocean avifauna.太平洋是岛栖苇莺（Acrocephalus）发生最重要物种分化的区域。在马克萨斯群岛（东波利尼西亚），苇莺隶属于两个独立抵达该群岛的不同演化支系。本研究借助线粒体序列（mitochondrial sequences）与微卫星标记（microsatellite markers），检测到两个演化支系间存在基因流，其中努库希瓦岛（Nuku Hiva）为二者的主要接触地带。随后，本研究采用反射光谱法（reflectance spectrometry），评估了所有种群的类胡萝卜素基羽色变异情况：马克萨斯苇莺在基于类胡萝卜素的羽色方面呈现趋同演化，但不同岛屿间的羽色变异仍十分显著。由于两个演化支系具有不同的系统发育起源，它们的黄色羽色为独立演化所得，且不同岛屿间的羽色还存在随机变异。最后，本研究对主要岛屿上的苇莺鸣唱进行了分析。多因素分析（multifactorial analysis）结果显示，马克萨斯苇莺的鸣唱在类群间存在细微差异，而岛屿间的显著差异则造就了不同的鸣唱方言。当不同演化支系的个体相遇时，鸣唱特征可能是主要的前合子隔离屏障（pre-zygotic barriers）。本研究为岛栖鸟类的羽色演化趋同现象提供了又一例证。此外，本研究强调了整合分析——结合遗传与表型性状——对于探究太平洋鸟类区系（avifauna）演化历史的重要意义。