The effects of heating on the behaviour ofOxytricha bifaria(Ciliophora, Hypotrichida)

Abstract

Experimental populations of the ciliate Oxytricha bifaria grown at 24°C were exposed to progressively higher temperatures in a thermally isotropic environment. Their behaviour was monitored and an ethogram was drawn for each step of the warming process (24, 29, and 34°C), as well as for three further periods of time after the temperature was brought back to the initial 24°C. As the temperature increased, (i) the percentage of mobile cells decreased (significantly at 34°C), (ii) their periods of immobilisation were more frequent; (iii) their average creeping velocity did not change; (iv) the radius of the arcs and the length of both the linear segments and the arcs decreased; (v) the frequency of the "side-stepping reaction" increased progressively, and (vi) it was often performed as bursts of reactions. Moreover, (vii) a new behavioural pattern, the "maximum-rotation reaction," was performed. When the ciliates were brought back to 24°C, their behavioural parameters, except for general mobility, did not return to normal values during the first 90 min. Linear heating of the experimental populations of O. bifaria induced nonlinear and time-stable effects on their behaviour (12 out of 17 parameters actually changed at 34°C).