Macroscopic robophysical model of turning in biflagellate algae

Single-cell algae exhibit diverse behaviors and are capable of goal-directed motion. Of interest is phototaxis, a light-triggered response during which algae swim and turn their eyespot towards a light source. While the photoreceptor responsible for this behavior has been characterized, the mechanics behind this response remain unknown. In Chlamydomonas, studies suggest that phototactic turning is mediated by differential changes in the beating frequency and amplitude of the flagella (Witman, 1996). To study algae turning, we developed a macroscopic motor-driven robophysical model (two flagella, body length of 8 cm) that swims in a viscous fluid (glycerin, 1,100 cSt) to replicate low Reynolds number swimming. We varied the frequency of one flagella (trans) while maintaining the other constant (cis). We observed that turning rate depended on the phase of the cis flagellum. When the cis flagellum was in the recovery phase, the robot achieved a rotation from 23– 34 degrees per cycle (deg/cyc). When the cis flagellum was in the power phase, the robot achieved a rotation of 8 – 13 deg/cyc. The results suggest that turning is sensitive to flagellar coordination. Preliminary experiments suggest feedback control can be implemented in the robot to generate autonomous phototactic turning.