Zoology and Evolutionary Biology, Department of Biology, University of Konstanz, Konstanz, Germany.
Zukunftskolleg, University of Konstanz, Konstanz, Germany.
Mol Biol Evol. 2017 Oct 1;34(10):2469-2485. doi: 10.1093/molbev/msx143.
Midas cichlid fish are a Central American species flock containing 13 described species that has been dated to only a few thousand years old, a historical timescale infrequently associated with speciation. Their radiation involved the colonization of several clear water crater lakes from two turbid great lakes. Therefore, Midas cichlids have been subjected to widely varying photic conditions during their radiation. Being a primary signal relay for information from the environment to the organism, the visual system is under continuing selective pressure and a prime organ system for accumulating adaptive changes during speciation, particularly in the case of dramatic shifts in photic conditions. Here, we characterize the full visual system of Midas cichlids at organismal and genetic levels, to determine what types of adaptive changes evolved within the short time span of their radiation. We show that Midas cichlids have a diverse visual system with unexpectedly high intra- and interspecific variation in color vision sensitivity and lens transmittance. Midas cichlid populations in the clear crater lakes have convergently evolved visual sensitivities shifted toward shorter wavelengths compared with the ancestral populations from the turbid great lakes. This divergence in sensitivity is driven by changes in chromophore usage, differential opsin expression, opsin coexpression, and to a lesser degree by opsin coding sequence variation. The visual system of Midas cichlids has the evolutionary capacity to rapidly integrate multiple adaptations to changing light environments. Our data may indicate that, in early stages of divergence, changes in opsin regulation could precede changes in opsin coding sequence evolution.
米达斯慈鲷鱼是中美洲的一个物种群，包含 13 个已被描述的物种，其历史可以追溯到几千年前，这是一个与物种形成很少相关的时间尺度。它们的辐射涉及到从两个浑浊的大湖中殖民到几个清澈的火山口湖。因此，米达斯慈鲷在其辐射过程中经历了广泛变化的光照条件。作为从环境到生物体的信息的主要信号传递者，视觉系统受到持续的选择性压力，是在物种形成过程中积累适应性变化的主要器官系统，特别是在光照条件发生剧烈变化的情况下。在这里，我们在机体和遗传水平上对米达斯慈鲷的整个视觉系统进行了表征，以确定在其辐射的短暂时间内进化出了哪些类型的适应性变化。我们表明，米达斯慈鲷具有多样化的视觉系统，其颜色视觉敏感性和晶状体透过率具有出乎意料的高种内和种间变异。与来自浑浊大湖的祖先种群相比，清澈火山口湖中的米达斯慈鲷种群在视觉敏感性方面发生了趋同进化，向较短的波长转移。这种敏感性的差异是由生色团使用、差异视蛋白表达、视蛋白共表达的变化以及编码序列变化的较小程度驱动的。米达斯慈鲷的视觉系统具有快速整合对不断变化的光照环境的多种适应性的进化能力。我们的数据可能表明，在分化的早期阶段，视蛋白调节的变化可能先于视蛋白编码序列进化的变化。
