Quantification of Flagellar Gait Changes with Combined Shape Mode Analysis and Swimming Simulations

TL;DR

This study combines shape mode analysis and swimming simulations to quantify how flagellar waveforms and swimming speeds of Chlamydomonas reinhardtii change with fluid viscosity, revealing that mean shape and beat frequency are key factors.

Contribution

It introduces a combined approach of shape mode analysis and simulations to understand flagellar gait changes with fluid rheology, highlighting the role of mean shape and frequency.

Findings

Flagellar mean shape significantly changes with viscosity.

Swimming speed variations are mainly due to mean shape and beat frequency.

Changes in the time-varying stroke are relatively subtle.

Abstract

Many different microswimmers propel themselves using flagella that beat periodically. The shape of the flagellar beat and swimming speed have been observed to change with fluid rheology. We quantify changes in the flagellar waveforms of Chlamydomonas reinhardtii in response to changes in fluid viscosity using (1) shape mode analysis and (2) a full swimmer simulation to analyze how shape changes affect the swimming speed and to explore the dimensionality of the shape space. By decomposing the gait into the time-independent mean shape and the time-varying stroke, we find that the flagellar mean shape substantially changes in response to viscosity, while the changes in the time-varying stroke are more subtle. Using the swimmer simulation, we quantify how the swimming speed is affected by the dimensionality of the flagellar shape reconstruction, and we show that the observed change in swimming speed with viscosity is explained by the variations in mean flagellar shape and beat frequency, while the changes in swimming speed from the different time-varying strokes are on the scale of variation between cells.