Hidden genetic diversity in the green alga Spirogyra (Zygnematophyceae, Streptophyta)

BMC Evolutionary Biology

Michael Schagerl²  Thomas Pröschold³  Michael HJ Barfuss¹  Charlotte Chen² 

[1] Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, Vienna, A-1030, Austria;Department of Limnology, University of Vienna, Althanstraße 14, Vienna A-1090, Austria;Department Applied Limnology, University of Rostock, Albert-Einstein-Str. 3, Rostock, D-18059, Germany

关键词: Diversity;    SSU rDNA;    Spirotaenia;    Sirogonium;    Spirogyra;    Non-homoplasious synapomorphy;    Zygnematophyceae;    Zygnematales;   

Others  :  1141162
DOI  :  10.1186/1471-2148-12-77

 received in 2012-03-22, accepted in 2012-05-07,  发布年份 2012

【 摘 要 】

Background

The unbranched filamentous green alga Spirogyra (Streptophyta, Zygnemataceae) is easily recognizable based on its vegetative morphology, which shows one to several spiral chloroplasts. This simple structure falsely points to a low genetic diversity: Spirogyra is commonly excluded from phylogenetic analyses because the genus is known as a long-branch taxon caused by a high evolutionary rate.

Results

We focused on this genetic diversity and sequenced 130 Spirogyra small subunit nuclear ribosomal DNA (SSU rDNA) strands of different origin. The resulting SSU rDNA sequences were used for phylogenetic analyses using complex evolutionary models (posterior probability, maximum likelihood, neighbor joining, and maximum parsimony methods). The sequences were between 1672 and 1779 nucleotides long. Sequence comparisons revealed 53 individual clones, but our results still support monophyly of the genus. Our data set did not contain a single slow-evolving taxon that would have been placed on a shorter branch compared to the remaining sequences. Out of 130 accessions analyzed, 72 showed a secondary loss of the 1506 group I intron, which formed a long-branched group within the genus. The phylogenetic relationship to the genus Spirotaenia was not resolved satisfactorily. The genetic distance within the genus Spirogyra exceeded the distances measured within any other genus of the remaining Zygnemataceae included in this study.

Conclusion

Overall, we define eight distinct clades of Spirogyra, one of them including the genus Sirogonium. A large number of non-homoplasious synapomorphies (NHS; 114 NHS in total) was found for Spirogyra (41 NHS) and for each clade (totaling 73 NHS). This emphasizes the high genetic diversity of this genus and the distance to the remaining Zygnematophyceae.

【 授权许可】

   
2012 Chen et al.; licensee BioMed Central Ltd; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

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