Vision represents an excellent model for studying adaptation, given the genotype‐to‐phenotype map that has been characterized in a number of taxa. Fish possess a diverse range of visual sensitivities and adaptations to underwater light, making them an excellent group to study visual system evolution. In particular, some speciose but understudied lineages can provide a unique opportunity to better understand aspects of visual system evolution such as opsin gene duplication and neofunctionalization. In this study, we showcase the visual system evolution of neotropical Characiformes and the spectral tuning mechanisms they exhibit to modulate their visual sensitivities. Such mechanisms include gene duplications and losses, gene conversion, opsin amino acid sequence and expression variation, and A₁/A₂‐chromophore shifts. The Characiforms we studied utilize three cone opsin classes (SWS2, RH2, LWS) and a rod opsin (RH1). However, the characiform's entire opsin gene repertoire is a product of dynamic evolution by opsin gene loss (SWS1, RH2) and duplication (LWS, RH1). The LWS‐ and RH1‐duplicates originated from a teleost specific whole‐genome duplication as well as characiform‐specific duplication events. Both LWS‐opsins exhibit gene conversion and, through substitutions in key tuning sites, one of the LWS‐paralogues has acquired spectral sensitivity to green light. These sequence changes suggest reversion and parallel evolution of key tuning sites. Furthermore, characiforms' colour vision is based on the expression of both LWS‐paralogues and SWS2. Finally, we found interspecific and intraspecific variation in A₁/A₂‐chromophores proportions, correlating with the light environment. These multiple mechanisms may be a result of the diverse visual environments where Characiformes have evolved.

中文翻译：

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Characiformes中的视觉色素进化：硬骨鱼全基因组复制，存活的视蛋白和光谱调节之间的动态相互作用。

鉴于在许多分类群中都有特征的基因型到表型图谱，视觉是研究适应性的绝佳模型。鱼具有各种各样的视觉敏感度和对水下光的适应性，使其成为研究视觉系统进化的极佳群体。特别是，一些特定但未被充分研究的谱系可以提供一个独特的机会，以更好地了解视觉系统进化的各个方面，例如视蛋白基因复制和新功能化。在这项研究中，我们展示了新热带Characiformes的视觉系统演化以及它们展现出的调节其视觉敏感性的光谱调谐机制。这些机制包括基因重复和丢失，基因转化，视蛋白氨基酸序列和表达变异以及A ₁ / A ₂发色团移位。我们研究的Characiforms利用三种视锥蛋白类别（SWS2，RH2，LWS）和棒视蛋白（RH1）。但是，characiform的整个视蛋白基因库是视蛋白基因缺失（SWS1，RH2）和重复（LWS，RH1）动态进化的产物。LWS和RH1重复起源于硬骨鱼特定的全基因组复制以及字符型特定的复制事件。两种LWS-视蛋白都具有基因转化功能，并且通过在关键调节位点进行取代，LWS-paralogues之一已获得了对绿光的光谱敏感性。这些序列变化表明关键调音位点的还原和平行进化。此外，characiforms的色彩视觉是基于LWS-paralogues和SWS2的表达。最后，我们发现A _1中的种间和种内变异/ A _2发色团的比例，与光环境有关。这些多种机制可能是Characiformes进化的多种视觉环境的结果。