Trying so hard but going nowhere: Swimming of drugged Daphnia magna

Daphnia or water fleas are millimeter sized microcrustaceans commonly studied as model organism in ecology, ecotoxicology and evolutionary biology. They propel themselves through water using powerstroke motion, by periodically beating their antennae. These antennae movements change dynamically to achieve particular swimming gaits whose descriptions in the literature have been qualitative and vaguely quantitative. Our study creates a granular level quantitative classification of baseline motion parameters of these swimming gaits. To further study the impact of these gaits on the dynamics, speed and efficiency of swimming, we treated these organisms with a dopamine receptor agonist. This drug is known to decrease the average swimming speed of the daphnids, however the exact physical mechanism by which that happens remains unclear. We image the beat patterns of the Daphnia antennae using high-speed video microscopy. By tracking the position and shape of the antennae during the beating cycle, we identify the features of the swimming gait that lead to emergence of distinct mobility patterns that decreases their overall speed.