Morphological and genetic variability of assemblages of Cyclotella ocellata Pantocsek/C. comensis Grunow complex (Bacillariophyta, Thalassiosirales)

Abstract

Centric diatom taxa in the Cyclotella ocellata and C. comensis complexes show high morphological variability and often apparently continuous morphological transitions. In this study, we investigated natural assemblages of the C. ocellata/C. comensis complex from Hungarian and Croatian lakes and from Turkish streams using morphological and molecular methods. The studied assemblages contained cells with morphologies resembling C. ocellata as well as other, closely related, species: C. comensis, C. pseudocomensis, C. costei, and C. trichnoidea. The goal of our paper was to assess whether the observed morphological differences were due to intraspecific variability or suggest the existence of several, putatively distinct species.

Ten morphometric characters were measured, which, either individually, or in pairs, did not differentiate the nominal taxa in our assemblages. However, multivariate discriminant analysis has revealed a group including C. ocellata and C. trichonidea morphologies could be separated from another containing C. comensis, C. pseudocomensis and C. costei.

A nuclear (18S rDNA) and a chloroplast (rbcL) gene were amplified and partially sequenced from environmental DNA or from isolated cells. The sequences showed little variability among the assemblages and nominal species. Although general congruence of molecular and morphometric separation supports the species level separation of C. ocellata/trichonidea from the probably conspecific C. comensis/pseudocomensis/costei, sequence divergences between the groups are in the same range as within them, so that a conspecificity of all four taxa cannot be unequivocally excluded.

Keywords:

• Cyclotella ocellata
• Cyclotella comensis
• European and Turkish assemblages
• morphometric analysis
• 18S rDNA
• rbcL

Acknowledgements

This research was conducted at the MTA Centre for Ecological Research, Danube Research Institute, H-1113 Budapest, Karolina út 29, Hungary and in the Department of Microbiology, Institute of Biology, Eötvös Loránd University, H-1117 Budapest Pázmány Péter sétány 1/C, Hungary.

The authors would like to thank Sonja Kistenich, Mirko Dreßler and Dr. Thomas Hübener for the C. costei, C. comensis and C. pseudocomensis sequences, Neela Enke, Regine Jahn and Bánk Beszteri and two anonymous reviewers for their valuable comments on the manuscript, Paul Thatcher, Zsuzsa Szilágyi and Virág Pozderka for the language correction. This study was supported by Hungarian National Science Foundation [KTIA-OTKA 80140] and also received support from the Turkish National Science Foundation [TUBITAK-116Z004].

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

Supplemental data for this article can be accessed at the Taylor & Francis website, doi: 10.1080/0269249X.2015.1101402