Sensitivity of Paramecium Thermotaxis to Temperature Change

Abstract

SYNOPSIS. The relationship to swimming velocity of the critical temperature gradient necessary for inducing thermotaxis in Paramecium caudatum was analyzed at various temperatures and viscosities. Since the critical temperature gradient was linearly proportional to the inverse of the swimming velocity, it is concluded that P. caudatum detects temperature changes by locomotion through space and thus exhibits thermotaxis, provided the rate of change is > 0.055 C/sec. The swimming velocity jump was observed when the ciliates were subjected to a stepwise temperature change toward an optimum with a rate > 0.05 C/sec; the jump was not observed, however, when they were subjected to a change toward an unpreferred temperature with the same rate. Hence, thermotaxis can be explained partly by the swimming velocity jump brought about when the cells are swimming toward an optimum temperature in a spatial gradient. It is suggested that thermotaxis might be a direct manifestation of the dynamic properties of membrane as a receptor.