Abstract

Hybrid zones are powerful natural settings for investigating how birds diversify into distinct species. Here we present the first genomic-scale exploration of the Baltimore (Icterus galbula) and Bullock’s (I. bullockii) oriole hybrid zone, which is notable for its long history of study and for its prominence in debates about avian species concepts and species limits. We used a reduced-representation sequencing approach to generate a panel of 3,067 genetic markers for 297 orioles sampled along the Platte River, a natural west-to-east transect across the hybrid zone. We then explored patterns of hybridization and introgression by comparing variation in genomic and plumage traits. We found that hybridization remains prevalent in this area, with nearly all orioles within the hybrid zone showing some degree of genomic mixing, and 41% assigned as recent-generation (F1/F2) hybrids. The center and width of the genomic and plumage gradients are concordant and coincident, supporting our finding that classically scored plumage traits are an accurate predictor of pure vs. hybrid genotypes. We find additional support for previous suggestions that the center of this hybrid zone has moved westward since it was first intensively sampled in the 1950s, but that this westward movement had slowed or ceased by the 1970s. Considered in concert, these results support previous inferences that some form of ongoing selection is counteracting the potential homogenization of these orioles via hybridization, thereby supporting their continued taxonomic separation as distinct species.

中文翻译：

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有争议的巴尔的摩和布洛克的黄ori杂交区的基因组和羽毛变化

摘要

混合区是研究鸟类如何多样化成不同物种的强大自然环境。在这里，我们介绍了巴尔的摩（Icterus galbula）和布洛克（I. bullockii）的首次基因组规模的探索）黄ole杂种带，以其悠久的研究历史和在有关鸟类物种概念和物种限制的辩论中的突出地位而著称。我们使用了减少表示法的测序方法，生成了沿普拉特河采样的297个金莺的3,067个遗传标记，这是横跨混合区的自然西向东样带。然后，我们通过比较基因组和羽毛特征的变异来探索杂交和基因渗入的模式。我们发现杂交在该区域仍然很普遍，杂种区内几乎所有的黄莺都表现出一定程度的基因组混合，其中41％被指定为近代（F1 / F2）杂种。基因组和羽毛梯度的中心和宽度是一致且重合的，这支持了我们的发现，即经典评分的羽毛特征是纯净vs.准确预测。杂种基因型。自从1950年代首次对其进行密集采样以来，这个混合区的中心一直向西移动，但到1970年代这种向西移动已经减慢或停止了，我们发现对于以前的建议还有更多的支持。一致认为，这些结果支持了先前的推论，即某种形式的正在进行的选择正在抵消这些黄via通过杂交的潜在同质化，从而支持它们作为不同物种的持续分类学分离。