Ciliary-based propulsion of Paramecium aurelia under varying viscosity

Abstract

Paramecia swim along helical trajectories propelled by the coordinated beating of the thousands of cilia covering their bodies. We have investigated how the swimming of populations of paramecium aurelia changes their swimming trajectories with varying viscosity, η, of their swimming medium to obtain their motor characteristics. The swimming speed distributions for 1 cP < η < 5.2 cP are Gaussian. The average instantaneous speed, v, and the variance, Δv, decrease monotonically with η. Simultaneously, their helical trajectories monotonically develop a greater pitch and radius. The product ηv is roughly constant over this factor of 5 change in η, indicating that paramecia aurelia swim with a constant propulsive force. Here, we present a phenomenological model of the beating cilia that produces the helical trajectory with a minimum number of swimming parameters. The model implies that the beat frequency of the body cilia decreases with increasing viscosity. The decrease can account for most of the observed decrease in swimming speed with η. We also find that the frequency of the cilia beating in the oral groove, which draws nutrients in, changes little with viscosity in sharp contrast with the body cilia responsible for propulsion.