ROLE OF ENDOSYMBIOTIC ALGAE IN PHOTOKINESIS AND PHOTOPHOBIC RESPONSES OF CILIATES

Abstract— The photobehavior of the ciliates Climacostomuum virens, Euplotes daidaleos and Paramecium bursaria associated with endosymbiotic green algae (Chlorella sp.) was compared with that of aposymbiotic ciliates (ciliates free of algae) and with the always aposymbiotic Paramecium arcticum. The aposymbiotic ciliates showed step‐up photophobic responses. The responses were more frequent and occurred at lower light intensities when the organisms contained endosymbiotic algae. In contrast, step‐down photophobic responses and photoaccumulations, as well as photokinesis, were never observed in aposymbiotic cells. These responses could be found only in ciliates when endosymbionts were present with the exception of C. virens, which showed none of these photoresponses.