Data from: Controlled iris radiance in a diurnal fish looking at prey

Active sensing using light, or active photolocation, is only known from deep sea and nocturnal fish with chemiluminescent "search" lights. Bright irides in diurnal fish species have recently been proposed as a potential analogue. Here, we contribute to this discussion by testing whether iris radiance is actively modulated. The focus is on behaviourally controlled iris reflections, called "ocular sparks". The triplefin Tripterygion delaisi can alternate between red and blue ocular sparks, allowing us to test the prediction that spark frequency and hue depend on background hue and prey presence. In a first experiment, we found that blue ocular sparks were significantly more often "on" against red backgrounds, and red ocular sparks against blue backgrounds, particularly when copepods were present. A second experiment tested whether hungry fish showed more ocular sparks, which was not the case. Again, background hue resulted in differential use of ocular spark types. We conclude that iris radiance through ocular sparks in T. delaisi is not a side effect of eye movement, but adaptively modulated in response to the context under which prey are detected. We discuss the possible alternative functions of ocular sparks, including an as yet speculative role in active photolocation.

基于光的主动感应，即主动光定位（active photolocation），目前仅在配备化学发光“搜寻”光源的深海及夜行性鱼类中被发现。近期有研究提出，昼行性鱼类的明亮虹彩可作为该机制的潜在类似物。本研究通过测试虹膜辐射是否可被主动调控，为该讨论提供新证据。研究聚焦于受行为调控的虹膜反射现象，即眼闪光（ocular sparks）。三鳍鳚（Tripterygion delaisi）可切换产生红色与蓝色的眼闪光，这使得我们能够验证如下假说：眼闪光的频率与色调取决于背景色调以及猎物是否存在。在首个实验中，我们发现当背景为红色时，蓝色眼闪光的激活概率显著更高；而背景为蓝色时，红色眼闪光的激活概率更高，这一效应在有桡足类动物存在时尤为明显。第二项实验测试了饥饿状态下的鱼是否会产生更多眼闪光，结果并未发现该现象。实验再次验证了背景色调会导致不同类型眼闪光的差异化使用。综上，三鳍鳚通过眼闪光产生的虹膜辐射并非眼球运动的副产物，而是会根据猎物探测的情境进行适应性调控。我们还讨论了眼闪光可能的其他功能，包括其在主动光定位中尚未被证实的推测性作用。