Non-visual opsins are transmembrane proteins expressed in the eyes and other tissues of many animals. When paired with a light-sensitive chromophore, non-visual opsins form photopigments involved in various non-visual, light-detection functions including circadian rhythm regulation, light-seeking behaviors, and seasonal responses. Here we investigate the molecular evolution of non-visual opsin genes in anuran amphibians (frogs and toads). We test several evolutionary hypotheses including the predicted loss of non-visual opsins due to nocturnal ancestry and potential functional differences in non-visual opsins resulting from environmental light variation across diverse anuran ecologies. Using whole-eye transcriptomes of 81 species, combined with genomes, multi-tissue transcriptomes, and independently annotated genes from an additional 21 species, we identify which non-visual opsins are present in anuran genomes and those that are also expressed in the eyes, compare selective constraint among genes, and test for potential adaptive evolution by comparing selection between discrete ecological classes. At the genomic level, we recovered all 18 ancestral vertebrate non-visual opsins, indicating that anurans demonstrate the lowest documented amount of opsin gene loss among ancestrally nocturnal tetrapods. We consistently found expression of 14 non-visual opsins in anuran eyes and detected positive selection in a subset of these genes. We also found shifts in selective constraint acting on non-visual opsins in frogs with differing activity periods, habitats, distributions, life histories, and pupil shapes, which may reflect functional adaptation. Although many non-visual opsins remain poorly understood, these findings provide insight into the diversity and evolution of these genes across anurans, filling an important gap in our understanding of vertebrate opsins and setting the stage for future research on their functional evolution across taxa.

中文翻译：

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青蛙非视觉视蛋白基因在环境、发育和形态适应中的多样性和分子进化

非视觉视蛋白是在许多动物的眼睛和其他组织中表达的跨膜蛋白。当与光敏发色团配对时，非视觉视蛋白形成感光色素，参与各种非视觉光检测功能，包括昼夜节律调节、寻光行为和季节性反应。在这里，我们研究了无尾两栖动物（青蛙和蟾蜍）非视觉视蛋白基因的分子进化。我们测试了几种进化假设，包括由于夜间祖先导致的非视觉视蛋白的预计损失，以及不同无尾动物生态中环境光变化导致的非视觉视蛋白的潜在功能差异。使用 81 个物种的全眼转录组，结合另外 21 个物种的基因组、多组织转录组和独立注释的基因，我们确定了无尾目基因组中存在哪些非视觉视蛋白以及眼睛中也表达的视蛋白，比较基因之间的选择约束，并通过比较离散生态类别之间的选择来测试潜在的适应性进化。在基因组水平上，我们恢复了所有 18 种祖先脊椎动物的非视觉视蛋白，这表明无尾目动物在祖先夜间活动的四足动物中表现出最低的视蛋白基因丢失量。我们一致发现无尾目眼睛中 14 种非视觉视蛋白的表达，并在这些基因的子集中检测到正选择。我们还发现，不同活动时期、栖息地、分布、生活史和瞳孔形状的青蛙对非视觉视蛋白的选择性约束发生了变化，这可能反映了功能适应。尽管许多非视觉视蛋白仍然知之甚少，但这些发现提供了对无尾目动物中这些基因的多样性和进化的深入了解，填补了我们对脊椎动物视蛋白理解的一个重要空白，并为未来研究它们在类群中的功能进化奠定了基础。