Predation risk of typical ovoid and ‘winged’ morphs of Euplotes (Protozoa, Ciliophora)

Freshwater species of the genus Euplotes (Protozoa, Ciliophora) change their morphology in the presence of some of their predators. The ciliates develop extended lateral ‘wings’ as well as dorsal and ventral projections which make engulfment by predators more difficult. In a series of laboratory experiments ingestion rates of four protozoan predators, the ciliates Lembadion bullinum, Dileptus anser, Stylonychia mytilus and Urostyla grandis, and one metazoan predator, the turbellarian Stenostomum sphagnetorum, on three species of Euplotes (E. octocarinatus, E. patella and E. aediculatus) were determined. It was calculated that the probability of rejection by a predator changed from 1:1 for ovoid morphs of Euplotes to about 2:1–20:1 for ‘winged’ morphs of Euplotes, dependent on the prey and predator species that were combined. The nutritional condition of the prey also had some influence. In mixed-species cultures of prey and predators, transformed cells of E. octocarinatus survived for several months.