Gait coordination and hydrodynamic performance of a quadriflagellate robophysical model

Multi-legged animals coordinate their limbs in distinctive patterns known as gaits. At the microscopic scale, quadriflagellate algae have been found to exhibit similar capabilities, coordinating their flagella to numerous rhythmic patterns to generate propulsion (Wan & Goldstein, 2016). To study quadriflagellate gait coordination, we developed a robophysical model which replicates quadriflagellate swimming at low-Reynolds number. We focus on two distinct gaits, the pronk and the trot, and explored the effects of flagellar orientation. When the flagella were oriented parallel to the cell body, forward motion was measured at 0.30±0.09 body lengths per gait cycle (BL/cyc) for the trot and at 0.19±0.03 BL/cyc for the pronk. Results are comparable to microorganisms’ performance, where using the trot enables a higher speed (0.39±0.18 BL/cyc) than the pronk (0.18±0.05 BL/cyc). Surprisingly, when the flagella beat planes were perpendicular to the cell body, hydrodynamic performance improved significantly. Forward motion was measured at 0.66±0.13 BL/cyc for the trot and at 0.38±0.10 BL/cyc for the pronk. The results show that hydrodynamic performance is highly sensitive to swimming gait and flagellar orientation.