# Run stop shock, run shock run: Spontaneous and stimulated gait-switching in a unicellular octoflagellate

## TL;DR

This study uncovers a novel tripartite motility pattern in an octoflagellate alga, revealing complex intracellular control over gait switching, including spontaneous shocks and quiescent stops, suggesting early evolution of signal transduction mechanisms.

## Contribution

The paper reports the discovery of a new tripartite motility pattern in an octoflagellate, highlighting intracellular control of gait switching and the presence of shock responses and quiescent states.

## Key findings

- Identified three distinct gaits: run, shock, and stop.
- Gait switching is weakly reversible in the reaction graph.
- Shocks can be spontaneous or mechanically triggered.

## Abstract

In unicellular flagellates, growing evidence suggests control over a complex repertoire of swimming gaits is conferred intracellularly by ultrastructural components, resulting in motion that depends on flagella number and configuration. We report the discovery of a novel, tripartite motility in an octoflagellate alga, comprising a forward gait ($run$), a fast knee-jerk response with dramatic reversals in beat waveform ($shock$), and, remarkably, long quiescent periods ($stop$) within which the flagella quiver. In a reaction graph representation, transition probabilities show that gait switching is only weakly reversible. Shocks occur spontaneously but are also triggered by direct mechanical contact. In this primitive alga, the capability for a millisecond stop-start switch from rest to full speed implicates an early evolution of excitable signal transduction to and from peripheral appendages.