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

Defensive function of trichocysts in Paramecium tetraurelia was tested against the heterotrophic heterotrich ciliate Climacostomum virens, which ingests various sizes of prey by means of a well-developed buccal apparatus. Trichocyst-non-discharge mutant and wild-type cells were compared as prey for this predator. The mutant cells were much more vulnerable than wild-type cells. Wild-type cells entering the buccal tube of Climacostomum often escaped by discharging trichocysts. We also studied the possible defensive function of backward swimming, which often follows Climacostomum-Paramecium interaction. The mutant incapable of backward swimming and wild-type cells escaped from C. virens in about the same frequency. Defensive function of trichocysts in Paramecium has been verified against the 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 does not have toxicysts. This work suggests that the trichocyst discharge may defend Paramecium from a variety of predators.