Several papers have been focused on providing taxonomic reports for symbiotic ciliates, some of them as general works, and a few directed to certain groups, and some were focused on certain geographic areas. The boundary between these categories sometimes is not clear, and there are frequent transitions between them. The symbiotic relationships can be categorized into mutualistic, commensalistic, or parasitic. This classification is based on several features: i) the dependence, where symbionts can be obligate or facultative ii) specificity of the symbionts iii) nutrients obtention, then biotrophic and necrotrophic symbionts are distinguished on the basis of whether nutrients are obtained from a living or dead partner, and iv) location of the symbionts, ectosymbionts or endosymbionts. ĭue to the diversity of symbioses, a classification system for symbiotic associations has been developed. The intricate associations are believed to have an essential driving force in evolutionary biology, as a host and their symbiotic microbiota acclimatize on scales of short time. This interaction is transmitted vertically (from one generation to the next) or horizontally (acquired de novo in each generation). The term symbiosis can be defined as a sustained relationship between at least two individuals from different species, either living in direct contact or close enough to each other during a part or the whole life cycles of the partners. These symbiotic ciliates have been reported in aerobic and anaerobic environments and from aquatic and terrestrial habitats. They belong to eight classes (Armophorea, Heterotrichea, Litostomatea, Nassophorea, Oligohymenophorea, Plagiopylea, Phyllopharyngea and Spirotrichea), 31 orders, 151 families, and almost 700 genera. ![]() This is equivalent to 33% of all the known species of the phylum. According to Corliss, 2,600 species of ciliates have been described as symbionts, mainly of individuals of metazoan phyla. ![]() *Address all correspondence to: IntroductionĬiliates (Alveolata: Ciliophora) comprise free-living and symbiotic species. Laboratório de Protozoologia, Instituto de Ciências Biológicas, Universidade Federal de Juiz de Fora, Brazil.Laboratório de Protozoologia, Programa de Pós-graduação em Biodiversidade e Conservação da Natureza, Universidade Federal de Juiz de Fora, Brazil.Laboratorio de Protozoología, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico.We propose new approaches for an integrative study of symbiotic ciliates. The analysis of the evolution of the life cycles complexity, exploring molecular data of the phases of the ciliate cycle in their hosts is also essential. The evolution of the symbiosis in ciliates demonstrates a higher diversification rate concerning free-living ciliates. At least three evolutionary routes can be traced: (1) transition from free-living to mutualism and parasitism, (2) transition from free-living to parasitism, and (3) regression from parasitism to free-living. Analysis of reconstructions of ancestral state evidence that the parasitism arose numerous times and independently among the lineages of ciliates. ![]() Some species are free-living as well symbionts, facultative symbionts, and obligate symbionts. Symbiosis, defined as an interaction between two species, is analyzed in this chapter to show a wide diversity of symbiotic systems in ciliates (epibiosis, commensalism, mutualism, and parasitism), providing some data about ciliate strategies showing their success as symbionts. Although many ciliates are free-living, more than 140 families of ciliates (Alveolata, Ciliophora) include symbiotic species of animals.
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