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Macroevolutionary analyses of ciliates associated with hosts support high diversification rates
Fabiola da Silva Costa1, Roberto Júnio Pedroso Dias1, Mariana Fonseca Rossi1
1Protozoology Laboratory (LabProto), Biological Sciences Institute, Federal University of Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil; Biodiversity and Nature Conservation Post-Graduation Program, Biological Sciences Institute, Federal University of Juiz de Fora, Minas Gerais, Brazil.
International Journal for Parasitology
|May 15, 2021
Summary
Parasitism is a recent adaptation in Ciliophora, evolving independently multiple times from free-living ancestors. Symbiotic ciliates show increased diversification rates compared to their free-living counterparts.
Area of Science:
- Microbiology
- Evolutionary Biology
- Protistology
Background:
- Ciliophora is a diverse phylum of microorganisms found in various environments, exhibiting a range of symbiotic relationships with metazoans, including mutualism and parasitism.
- While symbiotic relationships are widespread across Ciliophora phylogeny, their evolutionary history and the origins of parasitism remain poorly understood.
- Previous theoretical studies proposed two routes for parasitism development, but empirical investigation using molecular data has been limited.
Purpose of the Study:
- To infer a dated molecular phylogeny for the Ciliophora phylum using 18S rDNA gene sequences.
- To map the evolution of life habits, specifically symbiotic relationships, throughout Ciliophora's evolutionary history.
- To investigate whether symbiotic lifestyles are associated with variations in diversification rates and evolutionary modes within ciliates.
Main Methods:
- Construction of a comprehensive, time-calibrated molecular phylogeny for the phylum Ciliophora.
- Analysis of the 18S ribosomal DNA (rDNA) gene for phylogenetic inference.
- Mapping of life habits (free-living, mutualistic, parasitic) onto the inferred phylogeny to trace evolutionary transitions.
Main Results:
- The last common ancestor of Ciliophora was likely a free-living organism.
- Parasitism has evolved independently more than once in Ciliophora, primarily through two distinct pathways: free-living to mutualistic to parasitic, or direct evolution from free-living to parasitic.
- Parasitic and mutualistic ciliates exhibit significantly higher diversification rates when compared to their free-living relatives.
Conclusions:
- Parasitism represents a relatively recent evolutionary innovation within the Ciliophora phylum.
- The evolution of symbiotic relationships, particularly parasitism and mutualism, is linked to increased diversification rates in ciliates.
- Factors such as host interaction, colonization site, and host-provided conditions likely contribute to the evolutionary success of symbiotic ciliates.
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