Distinct gaits of self-propelled quadriflagellate microswimmers
Legged animals often coordinate multiple appendages for both underwater and terrestrial loco-motion. Quadrupeds in particular, change their limb movements dynamically to achieve a number of gaits, such as the gallop, trot, and pronk. Surprisingly, micron-sized unicellular algae are also capable of coordinating four flagella to produce microscale versions of these gaits for swimming. Here we present a fully-3D model of a quadriflagellate microswimmer comprising five beads and systematically investigate the effect of gait on swimming dynamics, propulsion speed, efficiency, and induced flow patterns. We find that by changing gait alone, distinct motility patterns emerge from the same basic microswimmer design. Our findings suggest that different species of morphologically-similar microorganisms (e.g. with identical number and placement of appendages) evolved distinct flagellar coordination patterns as a consequence of different ecological drivers. By comparing the flagella-induced flows in terms of volumetric clearance rate, we further explore the implications of distinct gaits for single-cell dispersal, feeding, and predator-avoidance.