Ref ID : 489
Tom Fenchel and Bland J. Finlay; Photobehavior of the ciliated protozoon Loxodes: taxic, transient, and kinetic responses in the presence and absence of oxygen. J.Protozool. 33(2):139-145, 1986
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Behavioral responses to light at different oxygen tensions were studied in the ciliate Loxodes striatus. In the absence of O2 it does not react to light. In the presence of O2 it reacts to light as if the pO2 had been further increased, with the induction of positive geotaxis, a transient phobic response, and finally with a permanent kinetic response (increased swimming velocity and a decreased rate of tumbling). Cells treated with cyanide behave as cells in an anoxic environment and do not react to light. It is concluded that the light response is due to the photochemical production of oxygen radicals and that the sensory receptors for O2 and for light are identical. The three types of behavioral response (geotaxis, transient, and kinetic responses) are discussed in terms of their adaptive significance for the orientation of Loxodes in the natural environment.