Title | ||
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Differentiation of a free-living alga into forms with ecto- and endosymbiotic associations with heterotrophic organisms in a 5-year microcosm culture. |
Abstract | ||
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The ecological mechanisms underlying the diversification of autotrophic species into endosymbiotic lifestyles and the ways in which the evolution of endosymbiotic species is ecologically and evolutionarily affected by sister lineages/lines that are adapted to extra-host environments remain unclear. In this paper, we investigated a differentiation process of algal species in which an endosymbiotic type was differentiated phenotypically from a free-living ancestral clone, by using an experimental model called the CET microcosm, which contains a green alga (Micractinium sp.), a bacterium (Escherichia coli), and a ciliate (Tetrahymena thermophila) cultured together without an external resource supply for over 5 years. We then analyzed the algal diversification process by comparing algal phenotypic properties regarding cell-aggregate formation and their effects on the survival of Tetrahymena (using a clone isolated on day 2668) in the absence of bacteria. We examined 13 Micractinium clones, including both ancestral and derived clones isolated from long-term (day 1819–1847) CET microcosm cultures. The results revealed that the free-living ancestral algal strain diversified in sympatry into an aggregate-forming type that associates with E. coli, and a non-aggregate-forming type that associates with Tetrahymena. Furthermore, a competition experiment revealed that the endosymbiotic (non-aggregate-forming) type was less adapted to the extracellular environment than the aggregate-forming type. This result suggests that severe competition with a nonendosymbiotic sister line in the extra-host environment favors the host-benefiting phenotype in an endosymbiotic line, because such symbionts can enhance the longevity of the host, thereby enabling the survival and reproduction of the symbiont within the host. |
Year | DOI | Venue |
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2015 | 10.1016/j.biosystems.2015.03.005 | Biosystems |
Keywords | Field | DocType |
Algae,Bacteria,Ciliates,Symbiosis,Evolution,Speciation,Selection | Symbiosis,Algae,Micractinium,Biology,Microcosm,Ciliate,Bacteria,Genetics,Tetrahymena,Autotroph | Journal |
Volume | ISSN | Citations |
131 | 0303-2647 | 0 |
PageRank | References | Authors |
0.34 | 3 | 5 |
Name | Order | Citations | PageRank |
---|---|---|---|
Toshiyuki Nakajima | 1 | 0 | 0.34 |
Yoshiyuki Fujikawa | 2 | 0 | 0.34 |
Toshiyuki Matsubara | 3 | 0 | 0.34 |
Mimi Karita | 4 | 0 | 0.34 |
Akiko Sano | 5 | 5 | 1.76 |