Benefits and costs of predator-induced morphological changes in the ciliate Colpidium kleini(Protozoa, Ciliophora)

Phenotypic transformation of C. kleinioccurred when the prey coexisted with the predatory ciliate Lembadion bullinumfor at least 24 hours, and was completed after 36–48 h. Net-separated predator medium caused visible shape changes in the prey. The induced phenotype was about 60% wider and 20% shorter than the typical one and had an almost spherical shape. The results showed that the induced morphological changes are a defense against L. bullinum, which is a raptorial feeder. In the presence of 100 predators, on an average 132 of 150 induced phenotypes survived for 2 h, but in the same conditions only 33 of 150 normal phenotypes did. The predator needed significantly more time and had to repeat attacks many times to catch and engulf the morphologically transformed prey. Only 16% of the attacks ended in ingestion of the transformed prey in less than 15 min, while in 54% of the cases the typical C. kleiniform was ingested during the first predator attack, which occurred in the first 2 min. The growth rate of induced C. kleiniphenotypes was on an average about 25% less than that of typical ones, indicating the substantial cost of the defense mechanism. Other predacious ciliates such as Dileptus margaritifer, Homalozoon vermiculareand Stylonychia mytilusdid not cause any morphological changes in C. kleini.