Enhanced predator detection by means of red fluorescence in a small fish species

几年来，我们一直在研究一种可能性，即生活在海底的小型鱼类可能会用它们的眼睛重新引导下沉的光线，以照亮它们周围几厘米远的环境。我们认为这提高了它们探测猎物或捕食者的能力，并将这种主动感知形式称为“昼夜主动光定位”。以前，我们能够证明我们的模型物种，三鳍雷公鱼，用它的眼睛积极地反射向下的阳光。研究发现，这种效应在浅水（约10米）中足够强，足以引起蝎鱼（Scorpaena porcus）瞳孔的反光。蝎鱼是一种隐蔽的坐等捕食者。行为实验和模型表明，三鳍鱼在距离捕食者7-12厘米的地方看到了这种自我诱导的反射，这可能是它们保持更多距离的原因。这段距离足以逃脱攻击。先前的实验也表明，当它们看到蝎子鱼时，相对于其他三种无害的视觉刺激，三鳍鱼会增加摆动行为的频率（=反复抬起头）。这让我们可以用摇摆来衡量警惕。在这个项目中，我们评估了浅水中的红光反射是否可以用于深度的局部照明。德莱西蝇的虹膜发出强烈的荧光。这在浅水中是不明显的，但在20米以下的昏暗的蓝绿色光线下很明显。2022年对122条三鳍进行的一项实验显示，在中性滤光片（所有波长都通过）下看到的蝎子鱼，比在阻挡红色的蓝绿色滤光片下看到的蝎子鱼摆动得更多。作为对照，它们对石头的反应引起的摆动要少得多，并且不受过滤器处理的影响。在后续的实验中，也就是本应用的主题中，我们现在想要具体地测试是否像隐含假设的那样，是蝎子鱼的眼睛引起了这种效果。使用类似的实验设计，我们将用3d打印的蝎子鱼模型来面对三鳍，这些模型安装了一个人工眼睛，可以反光，也可以不反光。我们预测三鳍对具有反射光瞳孔的模型显示出最大的摆动。第三个视觉刺激将是一条活的蝎子鱼，以确认第一个实验中的过滤器处理是可重复的，并评估在两种过滤器处理下，对反射眼睛的反应与对活蝎子鱼的反应相比如何。通过这种方法，我们希望提供进一步的证据，证明反向反射眼的存在是三鳍对视觉目标的差异反应的重要因素。

For several years, we have studied the possibility that small, bottom-dwelling fish may be using their eyes to re-direct downwelling light to illuminate their immediate environment over distances of a few centimetres. We think this improves their ability to detect prey or predators and call this form of active sensing “diurnal active photolocation”. Previously, we were able to show that our model species, the triplefin Tripterygion delaisi, actively reflects downwelling sunlight sideways with its eyes. This effect was found to be sufficiently strong in shallow water (~ 10 m) to induce retroreflective eyeshine in the pupil of the scorpionfish Scorpaena porcus, a cryptic sit-and-wait predator. Behavioural experiments and modelling suggested that triplefins see this self-induced reflexion in the predator’s pupil over distances of 7-12 cm, and that this is a possible reason why they keep more distance. This distance is sufficient to escape an attack. Previous experiments also demonstrated that triplefins increase the frequency of bobbing behaviour (= repeated head-raising) when they see a scorpionfish relative to three other, harmless visual stimuli. This allows us to use bobbing as a measure of wariness. In this project, we assess whether – in addition light reflection in shallow water – red fluorescence can be used for local illumination at depth. The iris of T. delaisi fluoresces strongly. This is inconspicuous in shallow water, but stands out under dim, blue-green light at depths below 20 m. An experiment in 2022 with 122 triplefins showed more bobbing in the visual presence of a scorpionfish when seen through a neutral filter (all wavelengths pass), than through a blue-green filter that blocks reds. Their response to a stone as a control elicited much less bobbing and was unaffected by the filter treatment. In a follow-up experiment, and the subject of this application, we now want to specifically test whether it is the eyes of a scorpionfish that induce the effect, as implicitly assumed. Using a similar experimental design, we shall confront triplefins with 3D-printed scorpionfish models that are fitted with an artificial eye that is either retroreflective or not. We predict that triplefins show most bobbing to the model with the retroreflective pupil. The third visual stimulus will be a live scorpionfish, to confirm that the filter-treatment in the first experiment is reproduceable, as well as to assess how the response to a retroreflective eye compares to that to a live scorpionfish under the two filter treatments. With this approach, we hope to provide further evidence that the presence of a retroreflective eye is an important contributor to the differential response of triplefins to a visual target.