RHYTHMICITY OF SWIMMING ACTIVITY IN AN AXENIC POPULATION OF PARAMECIUM-MULTIMICRONUCLEATUM

A unicellular organism, Paramecium, exhibits circadian rhythm activiti es in many physiological phenomena, i.e., mating reactivity, photoaccu mulation in Paramecium bursaria and mating type reversals in Parameciu m multimicronucleatum. In this study, we used an image-processing syst em to analyze swimming activity in a population of Paramecium multimic ronucleatum cultured axenically under 12 h-light/12 h-dark cycles (LD 12:12). Swimming behavior was recorded both under LD 12:12 and constan t darkness and images tracing the tracks of Paramecium were produced e very 4 min. Swimming activity was represented by the occupied area by the tracks relative to the total observed area. It is high during dayt ime and low at night and exhibits a free-running rhythm in constant da rkness. Furthermore, criteria for two major components of swimming beh avior, straight and circle swimming, were established and analyzed. Th e results indicate that swimming behavior alters depending on the time of day: straight swimming increased during the day and circling was d ominant around dusk both under LD 12:12 and constant darkness.