Visually guided swimming in box jellyfish: A study of swimming behaviour in response to visual stimuli

Abstract: Most animals use eyes to guide their behaviour. Analysing, and understanding, visually guided behaviours gets more complicated the more advanced the animal gets. Box jellyfish provide a relatively simple system for understanding visually guided behaviours. They have a limited nervous system, but they also possess a visual system that is quite impressive for a jellyfish. Box jellyfish have 24 eyes of four different eye types. For directional swimming the animals need to set swim speed and direction. In our investigations we measured how visual stimulation affected factors controlling swim speed and swim direction. As a model species we used the well studied box jellyfish species Tripedalia cystophora. In paper I we measured the pattern of bell movement of a tethered jellyfish in response to a simple visual stimulus. We found that animals responded to a darkening of a quarter of the underwater scene by increasing swim pulse frequency, producing off-centred openings in the bell and delaying contraction in one of the four sides of the bell. The increase in swim pulse frequency would make the animal swim faster, while the off-centred opening in the bell made the animal turn. In paper II we investigated how the four pacemakers that regulate the swim pulse frequency interact. We compared experimental data with the outcome of several different models and found a good fit to experimental data with a model where the pacemakers fully reset each other, in combination with a hyper-polarising pacemaker. All models underestimated the proportion of long inter-pulse intervals, implying the existence of an additional control mechanism. In paper III we measured the shape of the opening of the bell in response to different patterns of visual stimulation. We showed that the direction of the opening in the bell matches the pattern of stimulation. The opening of the bell was directed towards the middle of the dark area. When light intensity decreased all around the animal, centred openings in the bell where found. In paper IV we measured bell contraction patterns in response to increases in contrast or rate of light intensity decrease of the stimulus. Upon stimulation animals increased their swim pulse frequency. They slightly increased bell contraction, while the duration of the contraction phase of the swim pulse was not altered. Swim pulses where also more consistently directed at higher contrasts and higher rates of light-intensity decrease.