Defining the core group of the genus Gomphonema Ehrenberg with molecular and morphological methods

ABSTRACT

In order to understand the taxonomy and phylogeny of the genus Gomphonema, the type of the name of the genus, G. acuminatum, and related species complexes are studied with an integrative taxonomic approach. Sixty-seven unialgal Gomphonema strains were established from 34 different water bodies in Croatia, Faroe Islands, Finland, Iceland, Germany, Mexico, Spain, Switzerland and Korea, which provided molecular (18S and rbcL), morphometric and ultrastructural data. Our study was complemented by molecular data from INSDC, summing up the studied data to 82 freshwater Gomphonema strains from the G. acuminatum and related species complexes which are here defined as the Gomphonema core group. Except for outline variations which occur even within one clone, their micro-morphologies are indistinguishable. The molecular data of the two markers clustered the taxa of the core group into one clade, well differentiated from other Gomphonema taxa such as G. augur and G. parvulum. For differentiation within the clade, the plastid marker rbcL provided better species resolution comparable to traditionally recognized taxa. The combined analysis of the molecular as well as morphological data resulted in the defining of only 7 subclades in contrast to 20 currently assigned names for the taxa of the Gomphonema core group in this study. The Gomphonema core group has been overdescribed due to the use of outline as the main criterion for species delimitation. A polyphasic approach, combining molecular and micromorphological data for taxonomy, nomenclatural evaluation, and observations from clonal cultures can reveal the full intricacies of evolutionary relations.

KEYWORDS:

• Biogeography
• micro-morphology
• cladistics
• phylogeny
• Bacillariophyceae
• genodeme
• taxonomy
• new species

Acknowledgments

The authors are grateful to Jana Bansemer for sampling and cultivating, to Juliane Bettig and Monika Lüchow for support at the SEM, and to Michael Rodewald for help with the plates. Bart van de Vijver kindly provided data and images from the Van Heurck collection. The authors acknowledge funding by the Deutsche Forschungsgemeinschaft for SEM, for Names Registration, and by the BMBF for GBOL-2 Diatoms.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Bundesministerium für Bildung und Forschung [01LI1501E]; Deutsche Forschungsgemeinschaft [INST 130/839-1 FUGG; JA 874/8-1].

Notes on contributors

Nélida Abarca

Nélida Abarca is Algae Curator and Co-Head of the BGBM Research Group Diatoms, Freie Universität Berlin. Her focus is the phylogeny and taxonomy of diatoms with morphological and molecular methods. Contribution: identification, morphological and phylogenetic taxonomy, concept and main writing of the manuscript.

Jonas Zimmermann

Jonas Zimmermann is Head of the BGBM Research Group Diatoms, Freie Universität Berlin. His focus is on integrative taxonomy, DNA-Barcoding/Metabarcoding of diatoms for biodiversity and water quality assessments. Contribution: data analyses, performed the final phylogenetic analyses and gene trees, discussion of the results, writing of the corresponding parts and editing of the manuscript.

Wolf-Henning Kusber

Wolf-Henning Kusber is Data Curator of the BGBM Research Group Diatoms, Freie Universität Berlin. His focus is the nomenclature of algae; he runs the registration site PhycoBank. Contribution: typification and nomenclatural revision, editing of the manuscript.

Demetrio Mora

Demetrio Mora is currently Post Doc at the BGBM Research Group Diatoms, Freie Universität Berlin. Contribution: performed comparative phylogenetic analyses, assistance in writing and editing of the manuscript.

Anh T. Van

Anh T. Van did her M.Sc. study on diatoms at the BGBM Research Group Diatoms, Freie Universität Berlin, and is now a Doctorate Student at the University of Rostock Department of Applied Ecology and Phycology, Rostock, Germany. Contribution: performed laboratory work, early phylogenetic analyses.

Oliver Skibbe

Oliver Skibbe is Senior Researcher, BGBM Research Group Diatoms, Freie Universität Berlin. His specialty is the isolation and cultivation of uni-celled organisms such as diatoms. Contribution: isolation and cultivation of the strains, SEM,  editing the plates, discussion of the results.

Regine Jahn

Regine Jahn was Head of the BGBM Research Group Diatoms, Freie Universität Berlin until March 2019. She is officially retired but keeps on working as an Honorary Researcher. Contribution: conceived the topic, discussion of the results, some writing and editing of the manuscript.