Learning on a chip: Towards the development of trainable biohybrid sensors by investigating cognitive processes in non-marine Ostracoda via a miniaturised analytical system

Miniaturised analytical systems are showing growing interest in aquatic ecology, although this technology has not been exploited to study cognitive behaviours of organisms in aquatic micro-environments. Herein, a miniaturised testing arena was developed to investigate information processes and learning of Heterocypris incongruens, a freshwater ostracod relevant as bioindicator of environmental conditions. After dedicated training phases, a microchannel-based caging system enabled to tested if H. incongruens can associate a light stimulus to a food/stress source. Furthermore, the miniaturised system was used to test the ostracods ability in discriminating different coloured lights by choosing that previously associated with food or by avoiding the one previously associated with a stressor. Trained ostracods significantly reacted to light stimuli compared to naïve individuals. When two different light colours were provided, trained ostracods selected the one associated with food, and avoided that associated with a stress source. The experiment in which ostracods were trained to associate light to food showed that H. incongruens not only exploits visual stimuli for decision making, but also for modulating its behaviour, swimming longer in presence of the right colour light than in presence of the different colour light, or no light. This can be an adapting behaviour balancing the energy use during foraging activities and limiting exposure to potential predators. This study is the first to report such complex cognitive processes in ostracods, paving the way to new research directions for Lab-on-a-Chip systems, focused on behavioural ecology and cognition studies, as well as to the development of novel biohybrid sensors.