Electrophysiological responses of Didinium nasutum to Paramecium capture and mechanical stimulation

Abstract

Didinium nasutum is a carnivorous ciliate with a preference for feeding on species of Paramecium. Accidental contact between a Paramecium and the proboscis of a hungry Didinium (Fig. 1a) causes instantaneous discharge of extrusive organelles from the proboscis. If the strike is successful, some of these organelles penetrate the Paramecium, which immediately stops swimming and discharges many trichocysts, mostly from the struck side (Fig. 1b). Cytoplasmic streaming pulls the discharged organelles inward, the captured Paramecium reaches the proboscis, and then the Didinium swallows the prey, opening its proboscis^1–10 (Fig. 1c and d). On the other hand, a hungry Didinium does not discharge extrusive organelles when it collides with a glass wall. Instead it shows an avoiding reaction. When a Paramecium collides with the proboscis of a fed Didinium, the proboscis similarly does not discharge extrusive organelles, and the fed Didinium makes an avoiding response. We found that a hungry Didinium held steady by two glass capillary microneedles performed normal capture and ingestion in a solution containing Paramecium caudatum. We describe here an electrophysiological investigation of Didinium nasutum in collision with P. caudatum or with a glass rod while held still by glass capillary microneedles.