Synchrony and symmetry-breaking in active flagellar coordination

TL;DR

This paper reveals that unicellular algae coordinate flagellar movement through active pattern generation and symmetry-breaking mechanisms, enabling complex locomotion without neural systems.

Contribution

It demonstrates that flagellar coordination involves active rhythmogenesis and symmetry-breaking, acting as a central pattern generator in unicellular organisms.

Findings

Flagella exhibit intermittency and reversible rhythmogenesis.

Flagellar apparatus functions as a central pattern generator.

Symmetry-breaking mechanisms enable cell reorientation.

Abstract

Living creatures exhibit a remarkable diversity of locomotion mechanisms, evolving structures specialised for interacting with their environment. In the vast majority of cases, locomotor behaviours such as flying, crawling, and running, are orchestrated by nervous systems. Surprisingly, microorganisms can enact analogous movement gaits for swimming using multiple, fast-moving cellular protrusions called cilia and flagella. Here, I demonstrate intermittency, reversible rhythmogenesis, and gait mechanosensitivity in algal flagella, to reveal the active nature of locomotor patterning. In addition to maintaining free-swimming gaits, I show that the algal flagellar apparatus functions as a central pattern generator which encodes the beating of each flagellum in a network in a distinguishable manner. The latter provides a novel symmetry-breaking mechanism for cell reorientation. These findings imply that the capacity to generate and coordinate complex locomotor patterns does not require neural circuitry but rather the minimal ingredients are present in simple unicellular organisms.