The relative roles of natural and sexual selection in promoting evolutionary lineage divergence remains controversial and difficult to assess in natural systems. Local adaptation through natural selection is known to play a central role in promoting evolutionary divergence, yet secondary sexual traits can vary widely among species in recent radiations, suggesting that sexual selection may also be important in the early stages of speciation. Here, we compare rates of divergence in ecologically relevant traits (morphology) and sexually selected signalling traits (coloration) relative to neutral structure in genome‐wide molecular markers and examine patterns of variation in sexual dichromatism to explore the roles of natural and sexual selection in the diversification of the songbird genus Junco (Aves: Passerellidae). Juncos include divergent lineages in Central America and several dark‐eyed junco (J. hyemalis) lineages that diversified recently as the group recolonized North America following the last glacial maximum (ca. 18,000 years ago). We found an accelerated rate of divergence in sexually selected characters relative to ecologically relevant traits. Moreover, sexual dichromatism measurements suggested a positive relationship between the degree of colour divergence and the strength of sexual selection when controlling for neutral genetic distance. We also found a positive correlation between dichromatism and latitude, which coincides with the geographic axis of decreasing lineage age in juncos but also with a steep ecological gradient. Finally, we found significant associations between genome‐wide variants linked to functional genes and proxies of both sexual and natural selection. These results suggest that the joint effects of sexual and ecological selection have played a prominent role in the junco radiation.

中文翻译：

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在鸣禽属 Junco 的冰后辐射中，性信号特征的变化超过了生态梯度的形态差异

自然选择和性选择在促进进化谱系分化方面的相对作用仍然存在争议，并且难以在自然系统中进行评估。众所周知，通过自然选择进行的局部适应在促进进化分化方面发挥着核心作用，但在最近的辐射中，第二性征在物种之间可能存在很大差异，这表明性选择在物种形成的早期阶段也可能很重要。在这里，我们比较了与全基因组分子标记中的中性结构相关的生态相关性状（形态）和性选择信号性状（着色）的差异率，并检查了性二色性的变异模式，以探索自然和性选择在鸣禽属 Junco (Aves: Passerellidae) 的多样化。Juncos 包括中美洲的不同谱系和几个黑眼 junco (J. hyemalis) 谱系，这些谱系最近随着该群体在最后一次冰川盛期（大约 18,000 年前）之后重新定居北美而发生了多样化。我们发现，相对于生态相关性状，性选择特征的分化速度加快。此外，当控制中性遗传距离时，性别二色性测量表明颜色差异程度与性选择强度之间存在正相关关系。我们还发现二色性和纬度之间存在正相关，这与 juncos 谱系年龄下降的地理轴重合，但也与陡峭的生态梯度相吻合。最后，我们发现与功能基因相关的全基因组变异与性选择和自然选择的代理之间存在显着关联。这些结果表明，性选择和生态选择的联合效应在 junco 辐射中发挥了突出的作用。