Ciliary activity and the origin of metachrony in Paramecium: effects of increased viscosity.

The small dimensions of ciliary movement make viscosity of the medium a key factor in the hydrodynamic interaction of cilia. Because technical difficulties are encountered in direct observations of ciliary systems, little is known concerning the mechanisms by which the fluid medium actually influences the beat of cilia and metachronism. Gosselin (1958) observed in lateral cilia of mussel gills an increase in wave velocity when the viscosity was raised to 15 cP. Sleigh (1966), on the other hand, found that in increased viscosity Paramecium slowed down the frequency of the beat and the velocity of the metachronal wave and changed the metachronism from antiplectic to symplectic. Kuznicki, Jahn & Fonseca (1970) described an unpolarizedf, helicoidal travelling wave in the cilia of Paramecium swimming at normal and high viscosity. According to these authors metachrony is lost at the start of locomotion. The conclusions by Kuznicki et al. are not supported by my own observations made on swimming specimens at normal temperature and viscosity, which show a polarized beat in time and space and a dexioplectic metachrony (Machemer, 1972 a). Though it is widely accepted that metachronal patterns result from mechanical interactions of cilia, current hydrodynamic hypotheses (Gray, 1930; Machin, 1963; Jahn, 1964; Sleigh, 1966) do not explain certain systematic relations between ciliary activity and the parameters of metachronism. The present study was undertaken with the expectation that extensive variation of the viscosity of the medium would provide clues to the influence of this factor on the beating cilium and the coordination of movement in populations of cilia. The findings presented below have led to a working hypothesis of metachronal coordination which relates the parameters of this phenomenon to the spatio-temporal characteristics of the ciliary cycle.