Department of Experimental Psychology, Psychology Institute, University of São Paulo, Av. Professor Mello Moraes, 1721, Bloco A - D9. Butantã, São Paulo, CEP. 05508-030, Brazil.
Semin Cell Dev Biol. 2020 Oct;106:86-93. doi: 10.1016/j.semcdb.2020.04.004. Epub 2020 Apr 28.
Most vertebrates have duplex retinas, with two classes of photoreceptors, rods and cones. In the group of Snakes, however, distinct patterns of retinal morphology are associated with transitions between diurnal-nocturnal habits and reflect important adaptations of their visual system. Pure-cone, pure-rod and duplex retinas were described in different species, and this variability led Gordon Walls (1934) to formulate the transmutation theory, which suggests that rods and cones are not fixed entities, but can assume transitional states. Three opsin genes are expressed in retinas of most snake species, lws, rh1, and sws1, and recent studies have shown that the rhodopsin gene, rh1, is expressed in pure-cone retinas of diurnal snakes. This expression raised many questions about the nature of transmutation and functional aspects of the rhodopsin in a cone-like photoreceptor. Extreme differences in the retinal architecture of diurnal and nocturnal snakes also highlight the complexity of adaptations of their visual structures, which might have contributed to the adaptive radiation of this group and will be discussed in this review.
大多数脊椎动物都有双筒视网膜，有两种感光器，视杆细胞和视锥细胞。然而，在蛇类群体中，视网膜形态的明显模式与昼夜活动习性的转变有关，并反映了它们视觉系统的重要适应。在不同的物种中描述了纯锥细胞、纯杆细胞和双筒视网膜，这种可变性导致 Gordon Walls（1934 年）提出了“变态理论”，该理论表明视杆细胞和视锥细胞不是固定的实体，而是可以呈现过渡状态。大多数蛇类视网膜中表达三种视蛋白基因 lws、rh1 和 sws1，最近的研究表明，视蛋白基因 rh1 在昼行性蛇的纯锥细胞视网膜中表达。这种表达引发了许多关于变态的本质和类视蛋白在光感受器中的功能方面的问题。昼行性和夜行性蛇的视网膜结构的极端差异也突出了它们视觉结构适应的复杂性，这可能有助于该群体的适应性辐射，并将在本综述中讨论。
