The effects of fluid viscosity on the kinematics and material properties of C. elegans swimming at low Reynolds number

TL;DR

This study investigates how fluid viscosity influences the swimming kinematics and material properties of C. elegans, revealing that swimming speed remains constant while beating frequency decreases and tissue properties change with viscosity.

Contribution

It introduces a combined experimental and modeling approach to analyze how fluid viscosity affects nematode swimming behavior and tissue mechanics at low Reynolds number.

Findings

Swimming speed is nearly unaffected by viscosity changes.

Beating frequency decreases with increasing viscosity.

Young's modulus and tissue viscosity increase with fluid viscosity.

Abstract

The effects of fluid viscosity on the kinematics of a small swimmer at low Reynolds number are investigated in both experiments and in a simple model. The swimmer is the nematode Caenorhabditis elegans, which is an undulating roundworm approximately 1 mm long. Experiments show that the nematode maintains a highly periodic swimming behavior as the fluid viscosity is varied from 1.0 mPa-s to 12 mPa-s. Surprisingly, the nematode's swimming speed (~0.35 mm/s) is nearly insensitive to the range of fluid viscosities investigated here. However, the nematode's beating frequency decreases to an asymptotic value (~1.7 Hz) with increasing fluid viscosity. A simple model is used to estimate the nematode's Young's modulus and tissue viscosity. Both material properties increase with increasing fluid viscosity. It is proposed that the increase in Young's modulus may be associated with muscle contraction in response to larger mechanical loading while the increase in effective tissue viscosity may be associated with the energy necessary to overcome increased fluid drag forces.