Predator-prey interactions in ciliated protists

Protists appeared relatively early in evolution, about 1.8 billion years ago, soon after the first prokaryotic organisms. During this time period, most species developed a variety of behavioural, morphological, and physiological strategies intended to improve the ability to capture prey or to avoid predation. In this scenario, a key role was played by specialized ejectable membrane-bound organelles called extrusomes, which are capable to discharge their content to the outside of the cell in response to various stimuli. The aim of this chapter is to describe the two main strategies adopted in ciliate predator–prey interactions: 1) the first, mediated by mechanical mechanisms and involving, for example, extrusomes called trichocysts; 2) the second, mediated by toxic secondary metabolites and involving different kinds of chemical extrusomes.