Beer S, Wentzel C, Petie R, Garm A
Marine Biological Section, University of Copenhagen, Denmark.
Marine Biological Section, University of Copenhagen, Denmark.
Vision Res. 2016 Oct;127:28-34. doi: 10.1016/j.visres.2016.05.007. Epub 2016 Jul 26.
Photoreception in echinoderms has been studied for several years with a focus on the dermal photoreceptors of echinoids. Even though spatial vision has been proposed for this dermal photosystem, by far the most advanced system is found in a number of asteroids where an unpaired tube foot at the tip of each arm carries a proper eye, also known as the optical cushion. The eyes resemble compound eyes, except for the lack of true optics, and they typically have between 50 and 250 ommatidia each. These eyes have been known for two centuries but no visually guided behaviors were known in starfish until recently when it was shown that both Linckia laevigata and Acanthaster planci navigate their coral reef habitat using vision. Here we investigate the visual system of A. planci and find that they have active control of their visual field. The distalmost tube foot holding the eye is situated on a movable knob, which bends to adjust the vertical angle of the visual field. On the leading arms the visual field is directed 33° above the horizon, whereas the eyes on the trailing arms are directed 44° above horizontal on average. When the animal traverses an obstacle the knob bends and counteracts most of the arm bending. Further, we examined a previously described behavior, rhythmic arm elevation, and suggest that it allows the animal to scan the surroundings while preventing photoreceptor adaptation and optimizing image contrast.
棘皮动物的光感受研究已经开展了数年，重点是海胆类的真皮光感受器。尽管已经有人提出这种真皮光系统具有空间视觉，但迄今为止最先进的系统存在于一些海星中，在这些海星的每条触手末端有一个不成对的管足，其上带有一个合适的眼睛，也称为视垫。这些眼睛类似于复眼，只是没有真正的光学结构，通常每个眼睛有50到250个小眼。这些眼睛已经被发现两个世纪了，但直到最近才知道海星有视觉引导行为，当时发现光裸星虫和刺冠海星都利用视觉在珊瑚礁栖息地中导航。在这里，我们研究了刺冠海星的视觉系统，发现它们对视野有主动控制。握住眼睛的最远端管足位于一个可移动的瘤上，该瘤会弯曲以调整视野的垂直角度。在前进的触手上，视野平均指向地平线以上33°，而后退触手上的眼睛平均指向水平以上44°。当动物穿越障碍物时，瘤会弯曲并抵消大部分触手的弯曲。此外，我们研究了一种先前描述的行为，即有节奏的触手抬起，并认为这使动物能够扫描周围环境，同时防止光感受器适应并优化图像对比度。
