Data from: Variable light environments induce plastic spectral tuning by regional opsin coexpression in the African cichlid fish, Metriaclima zebra

Critical behaviours such as predation and mate choice often depend on vision. Visual systems are sensitive to the spectrum of light in their environment, which can vary extensively both within and among habitats. Evolutionary changes in spectral sensitivity contribute to divergence and speciation. Spectral sensitivity of the retina is primarily determined by visual pigments, which are opsin proteins bound to a chromophore. We recently discovered that photoreceptors in different regions of the retina, which view objects against distinct environmental backgrounds, coexpress different pairs of opsins in an African cichlid fish, Metriaclima zebra. This coexpression tunes the sensitivity of the retinal regions to the corresponding backgrounds and may aid in detection of dark objects, such as predators. Although intraretinal regionalization of spectral sensitivity in many animals correlates with their light environments, it is unknown whether variation in the light environment induces developmentally plastic alterations of intraretinal sensitivity regions. Here, we demonstrate with fluorescent in situ hybridization and qPCR that the spectrum and angle of environmental light both influence the development of spectral sensitivity regions by altering the distribution and level of opsins across the retina. Normally, M. zebra coexpresses LWS opsin with RH2Aα opsin in double cones of the ventral but not the dorsal retina. However, when illuminated from below throughout development, adult M. zebra coexpressed LWS and RH2Aα in double cones both dorsally and ventrally. Thus, environmental background spectra alter the spectral sensitivity pattern that develops across the retina, potentially influencing behaviours and related evolutionary processes such as courtship and speciation.

诸如捕食与择偶这类核心生命行为，通常依赖视觉系统。视觉系统对所处环境的光光谱具有敏感性，而不同生境内部以及生境之间的光光谱差异往往十分显著。光谱敏感性的演化改变，可推动物种分化与物种形成进程。视网膜的光谱敏感性主要由视觉色素决定，而视觉色素是结合了生色团（chromophore）的视蛋白（opsin）。我们近期在非洲慈鲷斑马拟丽鱼（Metriaclima zebra）中发现：视网膜不同区域的感光细胞，会针对各自对应的不同环境背景下的物体，共表达不同组合的视蛋白。这种共表达可使视网膜区域的敏感性适配对应的环境背景，或有助于侦测捕食者这类暗色目标。尽管诸多动物的视网膜光谱敏感性区域化特征与其光照环境存在关联，但目前尚不清楚光照环境的变化是否会诱导视网膜敏感性区域发生发育可塑性改变。本研究借助荧光原位杂交（fluorescent in situ hybridization）与实时定量聚合酶链式反应（qPCR）证实：环境光的光谱与入射角度，均可通过改变视蛋白在视网膜中的分布与表达水平，影响光谱敏感性区域的发育。通常情况下，斑马拟丽鱼（M. zebra）的腹侧视网膜双锥细胞（double cones）中，会共表达LWS视蛋白与RH2Aα视蛋白，而背侧视网膜双锥细胞则无此共表达现象。但如果在整个发育阶段均从下方给予光照，成年斑马拟丽鱼的背侧与腹侧视网膜双锥细胞中，均会共表达LWS视蛋白与RH2Aα视蛋白。由此可见，环境背景光的光谱会改变视网膜发育形成的光谱敏感性模式，进而可能影响相关行为以及求偶、物种形成这类相关演化过程。