Oxford University Museum of Natural History, University of Oxford, Parks Road, Oxford OX1 3PW, UK.
Stazione Zoologica Anton Dohrn, Via Francesco Caracciolo, 333, 80122 Naples, Italy.
J Exp Biol. 2021 Jun 1;224(11). doi: 10.1242/jeb.236653. Epub 2021 Jun 8.
Spatial vision was recently reported in a brittle star, Ophiomastix wendtii, which lacks discrete eyes, but little is known about its visual ecology. Our aim was to better characterize the vision and visual ecology of this unusual visual system. We tested animal orientation relative to vertical bar stimuli at a range of angular widths and contrasts, to identify limits of angular and contrast detection. We also presented dynamic shadow stimuli, either looming towards or passing the animal overhead, to test for potential defensive responses. Finally, we presented animals lacking a single arm with a vertical bar stimulus known to elicit a response in intact animals. We found that O. wendtii orients to large (≥50 deg), high-contrast vertical bar stimuli, consistent with a shelter-seeking role and with photoreceptor acceptance angles estimated from morphology. We calculate poor optical sensitivity for individual photoreceptors, and predict dramatic oversampling for photoreceptor arrays. We also report responses to dark stimuli moving against a bright background - this is the first report of responses to moving stimuli in brittle stars and suggests additional defensive uses for vision in echinoderms. Finally, we found that animals missing a single arm orient less well to static stimuli, which requires further investigation.
最近在一种缺乏离散眼睛的短腕海星（Ophiomastix wendtii）中报告了空间视觉，但其视觉生态学知之甚少。我们的目的是更好地描述这种不寻常视觉系统的视觉和视觉生态学。我们测试了动物相对于垂直条刺激的定向，范围包括角度宽度和对比度，以确定角度和对比度检测的极限。我们还呈现了动态阴影刺激，要么朝着动物上方逼近，要么从头顶掠过，以测试潜在的防御反应。最后，我们向缺少一条手臂的动物呈现了一个垂直条刺激，已知这个刺激会在完整的动物身上引起反应。我们发现，O. wendtii 会对大（≥50 度）、高对比度的垂直条刺激做出反应，这与寻求庇护所的作用以及从形态学估计的光感受器接受角度一致。我们计算出单个光感受器的光灵敏度很差，并预测光感受器阵列会进行大规模的过采样。我们还报告了对移动的暗刺激的反应，这是第一个在短腕海星中报告对移动刺激的反应的报告，并表明在棘皮动物中，视觉具有额外的防御用途。最后，我们发现缺少一条手臂的动物对静态刺激的定向能力较差，这需要进一步调查。
