Tashiro Juliana H, Ventura Dora F, Hauzman Einat
Department of Experimental Psychology, Psychology Institute, University of São Paulo, São Paulo, Brazil.
Front Neuroanat. 2022 Jan 26;15:770804. doi: 10.3389/fnana.2021.770804. eCollection 2021.
Snakes of the Viperidae family have retinas adapted to low light conditions, with high packaging of rod-photoreceptors containing the rhodopsin photopigment (RH1), and three types of cone-photoreceptors, large single and double cones with long-wavelength sensitive opsins (LWS), and small single cones with short-wavelength sensitive opsins (SWS1). In this study, we compared the density and distribution of photoreceptors and ganglion cell layer (GCL) cells in whole-mounted retinas of two viperid snakes, the lancehead and the rattlesnake , and we estimated the upper limits of spatial resolving power based on anatomical data. The ground-dwelling inhabits savannah-like habitats and actively searches for places to hide before using the sit-and-wait hunting strategy to ambush rodents. inhabits forested areas and has ontogenetic changes in ecology and behavior. Adults are terrestrial and use similar hunting strategies to those used by rattlesnakes to prey on rodents. Juveniles are semi-arboreal and use the sit-and-wait strategy and caudal luring to attract ectothermic prey. Our analyses showed that neuronal densities were similar for the two species, but their patterns of distribution were different between and within species. In adults and juveniles of , cones were distributed in poorly defined visual streaks and rods were concentrated in the dorsal retina, indicating higher sensitivity in the lower visual field. In adults of , both cones and rods were distributed in poorly defined visual streaks, while in juveniles, rods were concentrated in the dorsal retina and cones in the ventral retina, enhancing sensitivity in the lower visual field and visual acuity in the upper field. The GCL cells had peak densities in the temporal retina of and adults of , indicating higher acuity in the frontal field. In juveniles of , the peak density of GCL cells in the ventral retina indicates better acuity in the upper field. The estimated visual acuity varied from 2.3 to 2.8 cycles per degree. Our results showed interspecific differences and suggest ontogenetic plasticity of the retinal architecture associated with changes in the niche occupied by viperid snakes, and highlight the importance of the retinal topography for visual ecology and behavior of snakes.
蝰蛇科的蛇类拥有适应弱光条件的视网膜，其视杆光感受器高度密集，含有视紫红质光色素（RH1），还有三种视锥光感受器，即大型单视锥和双视锥，具有长波长敏感视蛋白（LWS），以及小型单视锥，具有短波长敏感视蛋白（SWS1）。在本研究中，我们比较了两种蝰蛇——矛头蝮和响尾蛇——全视网膜标本中光感受器和神经节细胞层（GCL）细胞的密度及分布，并根据解剖学数据估算了空间分辨能力的上限。地栖的矛头蝮栖息在类似稀树草原的栖息地，在采用坐等狩猎策略伏击啮齿动物之前，会积极寻找藏身之处。响尾蛇栖息在森林地区，其生态和行为有个体发育变化。成年响尾蛇生活在陆地上，采用与捕食啮齿动物的响尾蛇类似的狩猎策略。幼年响尾蛇半树栖，采用坐等策略和尾部引诱来吸引变温猎物。我们的分析表明，这两个物种的神经元密度相似，但它们在种间和种内的分布模式不同。在矛头蝮的成年和幼年个体中，视锥分布在界限不清的视觉带中，视杆集中在视网膜背侧，表明下视野的敏感度更高。在成年响尾蛇中，视锥和视杆都分布在界限不清的视觉带中，而在幼年响尾蛇中，视杆集中在视网膜背侧，视锥集中在视网膜腹侧，增强了下视野的敏感度和上视野的视敏度。GCL细胞在矛头蝮和成年响尾蛇的颞侧视网膜中密度最高，表明额视野的视敏度更高。在幼年响尾蛇中，GCL细胞在腹侧视网膜中的密度峰值表明上视野的视敏度更好。估计的视敏度在每度2.3至2.8周期间变化。我们的结果显示了种间差异，并表明蝰蛇科蛇类视网膜结构的个体发育可塑性与所占据生态位的变化相关，突出了视网膜地形图对蛇类视觉生态和行为的重要性。
