Collin Shaun P
Sensory Neurobiology Group, School of Biomedical Sciences, The University of Queensland, Brisbane, Australia.
Integr Zool. 2009 Mar;4(1):87-98. doi: 10.1111/j.1749-4877.2008.00138.x.
Lampreys (Agnatha) and lungfish (Dipnoi) are representatives of the earliest and the intermediate stages in vertebrate evolution, respectively, and survived in the Cambrian (approximately 540 mA, lampreys) and Devonian (approximately 400 mA, lungfishes) Periods. The unique phylogenetic position of these two groups presents us with an exciting opportunity to understand life in ancient times and to begin to trace the evolution of vision and photoreception in vertebrates. Using a multidisciplinary approach employing anatomical and molecular techniques, the evolution of photoreception is explored in these extant, living fossils to predict the environmental lighting conditions to which our vertebrate ancestors were exposed. Contrary to expectations, the retinae of the southern hemisphere lamprey (Geotria australis Gray, 1851) and the Australian lungfish (Neoceratodus forsteri Krefft, 1870) are far from "primitive," each possessing five types of photoreceptors, many with spectral filters for tuning the light. Detailed ultrastructural analysis reveals that all five receptor types in G. australis are cone-like, whereas N. forsteri possesses four cone types and a single type of rod. Each receptor type also contains a different visual pigment (opsin gene); that is, LWS, SWS1, SWS2, RhA and RhB in G. australis and LWS, SWS1, SWS2, Rh1 and Rh2 in N. forsteri, all of which are expressed within the retina and are sensitive to different parts of the electromagnetic spectrum, providing the potential for pentachromatic and tetrachromatic color vision, respectively.
七鳃鳗（无颌纲）和肺鱼（角齿鱼目）分别是脊椎动物进化最早阶段和中间阶段的代表，它们分别存活于寒武纪（约5.4亿年前，七鳃鳗）和泥盆纪（约4亿年前，肺鱼）。这两类生物独特的系统发育地位为我们提供了一个令人兴奋的机会，来了解古代的生命，并开始追溯脊椎动物视觉和光感受的进化历程。利用解剖学和分子技术的多学科方法，在这些现存的活化石中探索光感受的进化，以预测我们脊椎动物祖先所面临的环境光照条件。与预期相反，南半球七鳃鳗（Geotria australis Gray，1851）和澳大利亚肺鱼（Neoceratodus forsteri Krefft，1870）的视网膜远非“原始”，它们各自拥有五种光感受器，其中许多带有用于调节光线的光谱滤光器。详细的超微结构分析表明，澳大利亚七鳃鳗的所有五种感受器类型都是锥形的，而澳洲肺鱼有四种锥形类型和一种杆状类型。每种感受器类型还含有不同的视觉色素（视蛋白基因）；也就是说，澳大利亚七鳃鳗中有LWS、SWS1、SWS2、RhA和RhB，澳洲肺鱼中有LWS、SWS1、SWS2、Rh1和Rh2，所有这些都在视网膜内表达，并且对电磁光谱的不同部分敏感，分别提供了五原色和四原色视觉的潜力。
