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Microevolution and speciation in Thalassiosira weissflogii (Bacillariophyta).
Ulf Sorhannus1, Joseph D Ortiz, Matthias Wolf
1Department of Biology & Health Services, Edinboro University of Pennsylvania, Edinboro, Pennsylvania 16444, Edinboro, Pennsylvania 16444, USA. usorhannus@edinboro.edu
Protist
|December 19, 2009
Summary
Phylogeographic analysis of Thalassiosira weissflogii using molecular markers reveals distinct evolutionary pathways and biological species status across Atlantic and Pacific populations. Findings suggest potential reproductive isolation and complex diversification patterns.
Area of Science:
- Marine Diatom Phylogenetics
- Molecular Evolution
- Population Genetics
Background:
- Thalassiosira weissflogii is a globally distributed marine diatom with complex population structures.
- Understanding its phylogeography and biological species status is crucial for marine ecology and evolutionary studies.
- Previous studies have suggested geographic differentiation, but species boundaries remain debated.
Purpose of the Study:
- To infer phylogeographic differentiation of Thalassiosira weissflogii in the Atlantic and Pacific Oceans.
- To assess the biological species status of geographically distinct lineages using multiple molecular markers.
- To investigate the evolutionary history and reproductive isolation of different T. weissflogii strains.
Main Methods:
- Analysis of five different molecular markers, including ribosomal RNA, partial sexually induced gene 1 (Sig1), and partial beta-tubulin.
- Phylogenetic tree construction to infer evolutionary relationships and divergence patterns.
- Compensatory base change (CBC) analysis in ITS2 to assess reproductive isolation and biological species status.
Main Results:
- Ribosomal RNA data suggested an early evolution of the Hawaiian isolate, followed by divergence of Indonesian and Atlantic/California strains.
- Sig1 and beta-tubulin phylogenies indicated different divergence orders, with Sig1 supporting three biological species and beta-tubulin contradicting CBC analysis.
- ITS2 CBC analysis identified the Atlantic group (including California) as a single reproductive unit, and Indonesian and Hawaiian isolates as distinct biological species.
Conclusions:
- The study highlights conflicting phylogenetic signals among different markers, suggesting complex evolutionary histories for T. weissflogii.
- Concordance between ITS2 CBCs (a biological species marker) and Sig1 (involved in sperm-egg recognition) provides strong evidence for distinct biological species.
- The Pacific/Indonesian species complex likely evolved under gene flow and local environmental selection, with proposed hypotheses for Atlantic-California genetic similarities.
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