Morphological and taxonomic implications of the formation of colonies in Cyclostephanos and Stephanodiscus (Bacillariophyta)

ABSTRACT

The importance of diatoms in bioindication and palaeolimnology is significant. For these applications, and species identification in general, a sound understanding of morphological variability is essential. Some species of the centric diatom genera Cyclostephanos and Stephanodiscus can form long, chain-like colonies. In these genera colony formation is associated with the morphology of the spines, which hold the cells together. One objective of this study was to investigate other possible differences in the valve morphology of solitary and colonial cultures. In addition, all strains were sequenced to account for the possibility that solitary and colonial forms may be different species, using three different loci (LSU, rbcL, cox1). The results show that colony formation not only affects the spine morphology but also other morphological features of the valve. The current interpretation that C. invisitatus and C. delicatus are facultative colony formers is supported by the results of this study. The evidence furthermore suggests that C. incognitus is a morphotype of C. invisitatus. A similar morphological pattern leads to the hypothesis that S. hantzschii and S. binderanus could possibly be solitary and colonial forms of the same species, which is also in agreement with the molecular analysis. These findings have implications for the taxonomy of the group and its application and open up a way for future investigations of morphological changes due to colony formation in other groups and taxa.

HIGHLIGHTS

• Molecular data support facultative colony formation.

• Colony formation affects the valve morphology.

• Stephanodiscus hantzschii and S. binderanus may be conspecific.

KEYWORDS:

• Colony formation
• Cyclostephanos
• diatom taxonomy
• diatoms
• DNA barcoding
• LSU rDNA
• morphology
• rbcL
• Stephanodiscus
• taxonomy

Acknowledgements

We would like to thank Steffi Gottschalk, Sarah Haupt, Matthias Knie, Klaus-Peter Macke, Udo Nitschke, Eugen Rott and Susanne Schultz for their sampling efforts.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

K. Schultz: original concept, drafting, editing manuscript, sampling, cultures, molecular analysis, morphological analysis; M. Dreßler: editing manuscript, figure editing, sampling, cultures; O. Jacques: editing manuscript, sampling, cultures; M. Frank: electron microscopy; Armin Springer: electron microscopy; T. Hübener: editing manuscript, figure editing, sampling, cultures.

Additional information

Funding

This research was funded by the State Postgraduate Scholarship Program of the State of Mecklenburg-Vorpommern.