Eukaryotic swimming cells are shaped by hydrodynamic constraints

TL;DR

This study investigates how hydrodynamic constraints influence the shape of eukaryotic swimming cells, showing that their morphology often aligns with theoretical optima for propulsion efficiency and drag minimization.

Contribution

The paper demonstrates that the shapes of eukaryotic swimming cells are closely aligned with hydrodynamic efficiency and drag minimization principles, supported by analysis of a comprehensive cell motility database.

Findings

Flagella amplitude-to-wavelength ratio near theoretical optimum

Ciliate aspect ratios close to drag-minimizing predictions

Hydrodynamic constraints significantly influence cell shape

Abstract

Eukaryotic swimming cells such as spermatozoa, algae or protozoa use flagella or cilia to move in viscous fluids. The motion of their flexible appendages in the surrounding fluid induces propulsive forces that balance with the viscous drag on the cells and lead to a directed swimming motion. Here, we use our recently built database of cell motility (BOSO-Micro) to investigate the extent to which the shapes of eukaryotic swimming cells may be optimal from a hydrodynamic standpoint. We first examine the morphology of flexible flagella undergoing waving deformation and show that their amplitude-to-wavelength ratio is near the one predicted theoretically to optimise the propulsive efficiency of active filaments. Next, we consider ciliates, for which locomotion is induced by the collective beating of short cilia covering their surface. We show that the aspect ratio of ciliates are close to the one predicted to minimise the viscous drag of the cell body. Both results strongly suggest a key role played by hydrodynamic constraints, in particular viscous drag, in shaping eukaryotic swimming cells.