Hybrid speciation is rare in vertebrates, and reproductive isolation arising from hybridization is infrequently demonstrated. Here, we present evidence supporting a hybrid-speciation event involving the genetic admixture of the snow-capped (Lepidothrix nattereri) and opal-crowned (Lepidothrix iris) manakins of the Amazon basin, leading to the formation of the hybrid species, the golden-crowned manakin (Lepidothrix vilasboasi). We used a genome-wide SNP dataset together with analysis of admixture, population structure, and coalescent modeling to demonstrate that the golden-crowned manakin is genetically an admixture of these species and does not represent a hybrid zone but instead formed through ancient genetic admixture. We used spectrophotometry to quantify the coloration of the species-specific male crown patches. Crown patches are highly reflective white (snow-capped manakin) or iridescent whitish-blue to pink (opal-crowned manakin) in parental species but are a much less reflective yellow in the hybrid species. The brilliant coloration of the parental species results from nanostructural organization of the keratin matrix feather barbs of the crown. However, using electron microscopy, we demonstrate that the structural organization of this matrix is different in the two parental species and that the hybrid species is intermediate. The intermediate nature of the crown barbs, resulting from past admixture appears to have rendered a duller structural coloration. To compensate for reduced brightness, selection apparently resulted in extensive thickening of the carotenoid-laden barb cortex, producing the yellow crown coloration. The evolution of this unique crown-color signal likely culminated in premating isolation of the hybrid species from both parental species.

中文翻译：

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杂交物种导致亚马逊鸟的新的雄性次要性装饰

杂交物种在脊椎动物中很少见，很少显示出由杂交引起的生殖分离。在这里，我们提供的证据支持一种杂种形成事件，涉及亚马逊盆地雪域（Lepidothrix nattereri）和蛋白石冠状（Lepidothrix iris）柑桔的遗传混合物，从而导致了杂种的形成，即金黄色的加冕的柑（Lepidothrix vilasboasi）。我们使用了全基因组SNP数据集以及混合物，种群结构和聚结模型的分析来证明，金冠的麦甘在基因上是这些物种的混合物，并不代表杂种区，而是通过古老的遗传混合物形成的。我们使用分光光度法来量化物种特异性雄性冠冠的着色。在亲本物种中，冠状斑块具有高反射性的白色（白雪皑皑的manakin）或呈虹彩的发白蓝色至粉红色（蛋白石冠的manakin），但在杂种中的反射性则低得多。亲本物种的鲜艳颜色来自冠的角蛋白基质羽毛倒钩的纳米结构组织。但是，使用电子显微镜，我们证明了在两个亲本物种中该基质的结构组织是不同的，并且杂种是中间的。由于过去的掺混而导致的倒刺的中间性质似乎呈现出较钝的结构着色。为了补偿亮度降低，选择显然会导致富含类胡萝卜素的倒钩皮层大量增厚，产生黄色冠状着色。这种独特的冠色信号的进化可能最终导致过早从两个亲代物种中分离出杂交物种。选择显然导致富含类胡萝卜素的倒钩皮层大量增厚，产生黄色冠状着色。这种独特的冠色信号的进化可能最终导致过早地将杂种从两个亲本中分离出来。选择显然导致富含类胡萝卜素的倒钩皮层大量增厚，产生黄色冠状着色。这种独特的冠色信号的进化可能最终导致过早地将杂种从两个亲本中分离出来。