Defensive function of trichocysts in Paramecium tetraurelia against heterotrich ciliate Climacostomum virens

Defensive function of trichocysts in Paramecium tetraurelia was tested agai nst the heterotrophic heterotrich ciliate Climacostomum virens, which inges ts various sizes of prey by means of a well-developed buccal apparatus. Tri chocyst-non-discharge mutant and wild-type cells were compared as prey for this predator. The mutant cells were much more vulnerable than wild-type ce lls. Wild-type cells entering the buccal tube of Climacostomum often escape d by discharging trichocysts. We also studied the possible defensive functi on of backward swimming, which often follows Climacostomum-Paramecium inter action. The mutant incapable of backward swimming and wild-type cells escap ed from C. virens in about the same frequency. Defensive function of trichocysts in Paramecium has been verified against t he haptorian ciliates, Dileptus margaritifer and Monodinium balbiani, which have toxicysts as offensive organelles. In this work, we showed defensive function of trichocysts against the heterotrich ciliate C. virens, which do es not have toxicysts. This work suggests that the trichocyst discharge may defend Paramecium from a variety of predators.