Micro-Game Hunting: Predatory Behavior and Defensive Strategies in Ciliates

Using various feeding strategies ciliates consume all sizes of autotrophic cells from bacteria to the larger dinoflagellates or diatoms. In addition they consume other heterotrophic protists. In this way every component of prokaryotic and eukaryotic nanoproducer biomass can be transferred to higher trophic levels. Predator ciliates provide an intermediate level in the microbial loop and to obtain adequate information on their biology is important from an ecological point of view. On the other hand, effort spent in attempting to deepen our understanding of predation among protozoa are completely justified by the basic importance of this process. Protozoa, indeed, were not only the first primary consumers in the primeval Oceans, but the first predators as well. Such a new trophic niche is quite important, due to the two consequences it leads to: 1) it creates new empty spaces for new organisms to settle in; 2) it triggers a sort of evolutionary competition between predators and prey as to their morpho-functional acquisitions. So predation in protozoa offers a wide range of examples of more or less species specific and more or less direct cell interactions leading the organism to specific morphological or behavioral responses. Indeed if predators developed a variety of hunting strategies, the potential prey evolved defensive responses. Nevertheless there are not models exhaustively examined to obtain an overall picture of this phenomenon considered from a more specific sinecological point of view. This chapter deals with predation in ciliates. After an introduction to the various feeding strategies of ciliates and a survey of the ciliate predator-prey systems already studied by other authors, the model Amphileptus preying on Euplotes, is presented in more detail as a prototype of ciliate raptorial feeding behavior. Our attention is successively focused on: a) the ultrastructure of predator toxicysts (the hunting devices); b) the electrophysiological and ultrastructural effects of toxicysts discharge by Amphileptus on Euplotes; c) the behavioral patterns of the predator (prey recognition from a distance; nearby recognition; engulfment process); d) the peculiar digestion process; e) the defensive strategies of the prey.