Convergent phenotypic evolution of the visual system via different molecular routes: How Neotropical cichlid fishes adapt to novel light environments. Convergent evolution of cichlid vision

How predictable is evolution? This remains a fundamental but contested issue in evolutionary biology.When independent lineagescolonize the same environment, we are presented with a natural experiment that allows us to ask if genetic and ecologicaldifferences promote species-specific evolutionary outcomes or whether species phenotypically evolve in a convergent mannerin response to shared selection pressures. If so, are the molecular mechanisms underlying phenotypic convergence the same?In Nicaragua, seven species of cichlid fishes concurrently colonized two novel photic environments. Hence, their visual systemrepresents a compelling model to address these questions, particularly since the adaptive value of phenotypic changes is wellunderstood.By analyzing retinal transcriptomes, we found that differential expression of genes responsible for color vision (coneopsins and cyp27c1) produced rapid and mostly convergent changes of predicted visual sensitivities. Notably, these changesoccurred in the same direction in all species although there were differences in underlying gene expression patterns illustratingnonconvergence at the molecular level. Adaptive phenotypes evolved deterministically, even when species differ substantially inecology and genetic variation. This provides strong evidence that phenotypic evolution of the visual system occurred in responseto similar selective forces of the photic environment.KEY WORDS: Color vision, crater lake, cyp27c1, molecular

进化的可预测性究竟几何？这始终是进化生物学领域兼具基础性与争议性的核心议题。当独立演化的谱系拓殖至相同环境中时，便形成了一项天然实验——借此我们可以探究：遗传与生态差异是否会催生物种特异性的演化结果？抑或是物种会针对共同的选择压力，在表型层面以趋同演化的方式适应环境？若存在表型趋同，那么支撑该趋同的分子机制是否一致？

在尼加拉瓜，共有7种慈鲷鱼类同时拓殖了两种全新的光环境。因此，它们的视觉系统堪称解答上述问题的理想模型，尤其是在表型变化的适应价值已得到充分阐明的前提下。

通过对视网膜转录组进行分析，我们发现负责色觉的基因——视锥视蛋白（coneopsins）与cyp27c1——的差异表达，使得视觉敏感性的预测变化得以快速且整体上以趋同的方式产生。值得注意的是，尽管不同物种的底层基因表达模式存在差异，展现出分子层面的非趋同性，但所有物种的这类变化方向均保持一致。

即便不同物种在生态与遗传变异层面存在显著差异，适应性表型仍以确定性方式演化。这为视觉系统的表型演化是响应光环境的相似选择压力提供了强有力的证据。

关键词：色觉、火山口湖、cyp27c1、分子