| 1. |
- Logares, Ramiro, et al.
(författare)
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Extensive dinoflagellate phylogenies indicate infrequent marine-freshwater transitions
- 2007
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1095-9513 .- 1055-7903. ; 45:3, s. 887-903
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Tidskriftsartikel (refereegranskat)abstract
- We have constructed extensive 18S–28S rDNA dinoflagellate phylogenies (>200 sequences for each marker) using Maximum Likelihood and Bayesian Inference to study the evolutionary relationships among marine and freshwater species (43 new sequences). Our results indicated that (a) marine and freshwater species are usually not closely related, (b) several freshwater species cluster into monophyletic groups, (c) most marine–freshwater transitions do not seem to have occurred recently and, (d) only a small fraction of the marine lineages seem to have colonized fresh waters. Thus, it becomes apparent that the marine–freshwater boundary has acted as a barrier during the evolutionary diversification of dinoflagellates. Our results also shed light on the phylogenetic positions of several freshwater dinoflagellates which, to date, were uncertain.
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| 2. |
- Logares, Ramiro, et al.
(författare)
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Infrequent marine-freshwater transitions in the microbial world
- 2009
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Ingår i: Trends in Microbiology. - : Elsevier BV. - 0966-842X .- 1878-4380. ; 17:9, s. 414-422
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Forskningsöversikt (refereegranskat)abstract
- Until recently, the evolutionary relationships between marine and freshwater microbes were unclear, but the use of molecular phylogenies is beginning to shed light on this subject. An increasing amount of studies are showing that marine and freshwater microbes (including viruses) are usually not closely related, often grouping into distinct marine and freshwater phylogenetic clusters, similar to what has been reported before for macroorganisms. These studies indicate that marine–freshwater transitions have been infrequent events during the diversification of microbes and that most of these transitions occurred a long time ago in evolutionary terms. Here we discuss the significance of recent studies addressing this question and consider possible avenues for future research.
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| 3. |
- Logares, Ramiro, et al.
(författare)
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Phenotypically different microalgal morphospecies with identical ribosomal DNA: A case of rapid adaptive evolution?
- 2007
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Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 1432-184X .- 0095-3628. ; 53:4, s. 549-561
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Tidskriftsartikel (refereegranskat)abstract
- The agents driving the divergence and speciation of free-living microbial populations are still largely unknown. We investigated the dinoflagellate morphospecies Scrippsiella hangoei and Peridinium aciculiferum, which abound in the Baltic Sea and in northern temperate lakes, respectively. Electron microscopy analyses showed significant interspecific differences in the external cellular morphology, but a similar plate pattern in the characteristic dinoflagellate armor. Experimentally, S. hangoei grew in a wide range of salinities (0–30), whereas P. aciculiferum only grew in low salinities (0–3). Despite these phenotypic differences and the habitat segregation, molecular analyses showed identical ribosomal DNA sequences (ITS1, ITS2, 5.8S, SSU, and partial LSU) for both morphospecies. Yet, a strong interspecific genetic isolation was indicated by amplified fragment length polymorphism (F ST = 0.76) and cytochrome b (cob) sequence divergence (∼1.90%). Phylogenetic reconstructions based on ribosomal (SSU, LSU) and mitochondrial (cob) DNA indicated a recent marine ancestor for P. aciculiferum. In conclusion, we suggest that the lacustrine P. aciculiferum and the marine-brackish S. hangoei diverged very recently, after a marine–freshwater transition that exposed the ancestral populations to different selective pressures. This hypothetical scenario agrees with mounting data indicating a significant role of natural selection in the divergence of free-living microbes, despite their virtually unrestricted dispersal capabilities. Finally, our results indicate that identical ITS rDNA sequences do not necessarily imply the same microbial species, as commonly assumed.
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