Data from: Evolutionary dynamics of Rh2 opsins in birds demonstrate an episode of accelerated evolution in the New World warblers (Setophaga)

Low rates of sequence evolution associated with purifying selection can be interrupted by episodic changes in selective regimes. Visual pigments are a unique system in which we can investigate the functional consequences of genetic changes, therefore connecting genotype to phenotype in the context of natural and sexual selection pressures. We study the RH2 and RH1 visual pigments (opsins) across 22 bird species belonging to two ecologically convergent clades, the New World warblers (Parulidae) and Old World warblers (Phylloscopidae), and evaluate rates of evolution in these clades along with data from 21 additional species. We demonstrate generally slow evolution of these opsins: both Rh1 and Rh2 are highly conserved across Old World and New World warblers. However, Rh2 underwent a burst of evolution within the New World genus Setophaga, where it accumulated substitutions at 6 amino acid sites across the species we studied. Evolutionary analyses revealed a significant increase in dN/dS in Setophaga, implying relatively strong selective pressures to overcome long-standing purifying selection. We studied the effects of each substitution on spectral tuning and found they do not cause large spectral shifts. Thus substitutions may reflect other aspects of opsin function, such as those affecting photosensitivity and/or dark-light adaptation. Although it is unclear what these alterations mean for color perception, we suggest that rapid evolution is linked to sexual selection, given the exceptional plumage colour diversification in Setophaga.

与净化选择（purifying selection）相关的低序列进化速率，可因选择机制的间歇性改变而发生中断。视觉色素是一类独特的研究体系，可用于探究遗传变异的功能效应，进而在自然选择与性选择的压力背景下建立基因型与表型之间的关联。本研究针对两个生态趋同演化支系——新大陆森莺科（Parulidae）与旧大陆柳莺科（Phylloscopidae）的22种鸟类，对其RH2与RH1视觉色素（视蛋白，opsins）开展研究，并结合额外21个物种的序列数据，分析这两个支系内视蛋白的进化速率。研究结果表明，这类视蛋白整体进化速率较慢：RH1与RH2在新旧大陆的森莺类群中均呈现高度保守性。但在新大陆林莺属（Setophaga）类群中，RH2却经历了一次进化爆发：在所研究的物种中，该蛋白在6个氨基酸位点上积累了置换突变。进化分析显示，林莺属的dN/dS比值显著升高，暗示存在较强的选择压力以突破长期的净化选择。本研究探究了每一处置换突变对光谱调谐特性的影响，结果显示这些突变并未引发显著的光谱位移。因此，这些置换突变可能反映了视蛋白功能的其他维度，例如影响光敏感度或明暗适应的相关功能。尽管目前尚不清楚这些改变对颜色感知的具体影响，但鉴于林莺属鸟类存在极为显著的羽色多样化特征，我们推测其快速进化与性选择存在关联。