Expression of opsins, ultrastructure of eyes, and light-induced behaviour in tardigrades (water bears): Insights into the evolution of visual systems and photoreception in panarthropods

感知光的能力在动物中广泛分布，但这种复杂的感觉能力的进化尚未完全了解。我们的知识中有一个特别的空白是关于缓步动物（水熊）的视觉系统。尽管他们的关键系统发育的位置作为一个最接近的节肢动物亲属，不足的数据是可利用的光感受器和视觉器官的缓步动物的超微结构。此外，最近在缓步动物物种中发现的视蛋白基因表达的数据完全缺失，尽管这些蛋白质在光接收和光诱导行为中起着关键作用。因此，计划项目的主要目标是：㈠分析光感受器的超微结构，并对两个主要缓步动物亚群-异缓步动物和真缓步动物-的眼睛进行三维重建，因为这些数据将提供关于缓步动物眼睛视觉特性的基本信息;（ii）免疫定位所有已知来自缓步动物的视蛋白，以澄清这些蛋白中哪些与视觉有关，哪些是非视觉分子;（iii）研究缓步动物Hypsibius dujardini的趋光/光动力学行为，并检测该物种的光谱敏感性，以阐明它对哪些波长的光有反应。新的数据将有助于我们了解缓步动物的视觉和感光系统，并阐明其进化以来的三个主要泛节肢动物群的分歧：节肢动物，Onychophora和缓步动物。

The ability to perceive light is widely distributed among animals, but the evolution of this complex sensory capacity is not fully understood. One particular gap in our knowledge concerns the visual system of tardigrades (water bears). Despite their key phylogenetic position as one of the closest arthropod relatives, insufficient data are available on the ultrastructure of the photoreceptors and visual organs of tardigrades. Moreover, data on the expression of opsin genes, which have been identified recently in a tardigrade species, are completely missing, although these proteins play a key role in light reception and light-induced behaviour. The major goal of the planned project is therefore: (i) to analyse the ultrastructure of photoreceptors and to perform a 3D reconstruction of eyes in representatives of two major tardigrade subgroups, the Heterotardigrada and Eutardigrada, as these data will provide essential information on visual properties of the tardigrade eye; (ii) to immunolocalise all opsin proteins known from tardigrades in order to clarify which of these proteins are involved in vision and which ones are non-visual molecules; and (iii) to study the phototactic/photokinetic behaviour in the tardigrade Hypsibius dujardini and to examine the spectral sensitivity of this species to clarify to which wavelengths of light it responds. The new data will help us to understand the visual and photosensory system of tardigrades and to shed light on its evolution since the divergence of the three major panarthropod groups: Arthropoda, Onychophora, and Tardigrada.