Metachronal wave coordination encodes multimodal swimming in ciliated unicellular predators

Abstract

Motile cilia are slender cellular appendages, conserved across eukaryotes ranging from unicellular protists to humans, that beat to generate fluid flow. In most organisms, cilia form dense arrays of thousands of filaments that coordinate their motion into persistent, temporally synchronized patterns known as metachronal waves. Despite their ubiquity, the dynamics of these patterns and their role in tuning propulsion remain poorly understood. Here, we investigate how metachronal coordination shapes the navigation of Didinium nasutum, a highly agile unicellular predator with two circumferential ciliary bands. Using high-speed imaging of freely swimming cells, we capture and quantify the dynamics of metachronal wave coordination and track their evolution across different swimming states and transitions. Combining these measurements with a hydrodynamic model, we uncover how dynamic changes in coordination directly regulate propulsion and maneuverability. We show that stable metachronal waves support persistent directed swimming, local inhomogeneities in coordination give rise to curved trajectories, and global wave reversals accommodate rapid evasion-like reorientations. Our findings reveal that transitions between coordination modes allow Didinium to access a diverse swimming repertoire, highlighting dynamic ciliary patterning as a key mechanism to encode complex microscale navigation strategies. More broadly, they provide mechanistic insights into how metachronal coordination shapes fluid flows generated by dense ciliary arrays found in unicellular protists and airway epithelia alike, ultimately influencing swimming and transport in biological systems.