Symbiotic associations in ciliates: Ecological and evolutionary perspectives

Abstract

Ciliates can develop facultative or permanent symbiotic associations with other species. The ecological success of mixotrophic symbiosis in ciliates lead us to question the physiological aspects and the evolutionary processes by which such associations can emerge, be maintained, and evolve. We highlight the symbiotic interactions between ciliated protozoan and other organisms, and discuss the general and essential aspects of these associations from the ecological and evolutionary perspectives. We first overview the ecological role of mixotrophic protists and the major types of symbiotic associations in aquatic environments (Sects. 15.2 and 15.3). Subsequently, we review the mechanisms employed for partner recognition and selective acquisition, for the infection process of symbiotic cells, and the physiological regulation used by the ciliate hosts to control or exploit these symbionts (Sect. 15.4). Lastly, we introduce a non-reductionist approach, by using an experimental synthetic ecosystem, which focuses on how ecosystem processes affect the emergence and evolution of symbiotic associations (Sect. 15.5).