Clarifying confusion – Prorocentrum triestinum J.Schiller and Prorocentrum redfieldii Bursa (Prorocentrales, Dinophyceae) are two different species

ABSTRACT

The Prorocentrales are a unique group of dinophytes based on several apomorphic traits, but species delimitation is challenging within the group. Prorocentrum triestinum was described by Josef Schiller in 1918 as an important bloom-forming species from Trieste (Mediterranean, Adriatic Sea) with a conspicuous asymmetric outline and a small, asymmetrically located subapical spine. All subsequent records under this name fail to conform to Schiller’s original description. These inconsistencies have their origin in John Dodge’s 1975 revision of Prorocentrum, which placed Prorocentrum redfieldii, a more symmetrical, slender species with a long apical spine, into synonymy under P. triestinum. To clarify this confusion, we collected samples at the type locality of P. triestinum in Trieste and established a strain that is morphologically consistent with the protologue and suitable for use in epitypification. Morphology and rRNA sequence data of this strain were compared with four new strains identified as P. redfieldii from the Mediterranean Sea and the North Atlantic Ocean. Cells of P. triestinum had an asymmetric outline in lateral view and a small, dorso-subapical spine. These features, which are readily resolved by light microscopy, were distinct from those of the nearly symmetrical and slender cells of P. redfieldii, which had a long, apically located spine. The species are nevertheless closely related and share an identical architecture of the periflagellar area with a distinctive, largely reduced accessory pore together with a very small platelet 7. This apomorphy clearly differentiates both species from other species of Prorocentrum. Both species differ in their primary rRNA sequences, and ITS and LSU sequence differences will enable them to be distinguished in future meta-barcoding studies. The present study demonstrates that P. triestinum and P. redfieldii are distinct species and thus contributes to a reliable biodiversity assessment of Prorocentrum.

HIGHLIGHTS

Prorocentrum triestinum is characterised molecularly for the first time and delimited from P. redfieldii.

The identity of important bloom-forming species is clarified.

Structural details of the periflagellar area are described.

KEYWORDS:

• Diversity
• epitypification
• marine
• Mediterranean Sea
• microalgae
• North Atlantic
• phylogeny

Acknowledgements

MH thanks Nils Gülzow (Wilhelmshaven) for allocating his P. redfieldii strain from the German Bight. The authors are thankful to Dr Steve Pueppke (Michigan State University) for improving the English of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.1948614

Supplementary table S1. Voucher list. All names are given under the rules of the ICN, the author standard forms follow Brummitt & Powell (1992). Abbreviation: n. inf., no information; s.n., without number. If ‘holotype’ or ‘epitype’ is noted for a species name, then it refers to material from which the type was prepared.

Supplementary figures S1–S12. Prorocentrum redfieldii (strain 1033) LM. figs S1–S9. Living cells. figs S11, S12. Formaldehyde-fixed cells. figs S1–S9. General size and shape of cells in right lateral (figs S1, S2), in left lateral (figs S3, S4), in ventral (figs S5, S9) and in dorsal (figs S6–S8) view. Note the long apical trichocyst rods (arrows in figs S1, S7), the thick chromosomes (visible, e.g., in figs S1, S4, S7, S8), the presence of thecal pores (arrows) visible for the empty theca in fig. S10 and the presumptive pusule (p) in fig. S8. fig. S11. Cell with blue light excitation, when chlorophyll autofluorescence indicated chloroplast structure. fig. S12. DAPI stained cell with UV excitation to illustrate shape and position of the nucleus. Scale bars: 5 μm.

Supplementary figures S13–S20. Prorocentrum redfieldii (strain 1033) SEM, entire cells. fig. S13. Cell in right lateral view. fig. S14. Cell in left lateral view. fig. S15. Cell in left-lateral ventral view. figs S16, S17. Cells in ventral view. fig. S18. Cell in right-lateral dorsal view. figs S19, S20. Cells in dorsal view. Scale bars: 5 μm.

Supplementary figures S21–S242. Prorocentrum redfieldii (strain 1033), detailed SEM of surface structure, pores and of the periflagellar area. figs S21, S22. Large tubular and small pores in external (fig. S21) and internal (fig. S22) view. Note the presence of a mini-pore located posterior at the antapex (white arrow in fig. S21), which is distinctly smaller than a small pore (black arrow in fig. S21). figs S23, S24. Detailed view of the periflagellar area of the same cell in two different magnifications. ap = accessory pore, fp = flagellar pore. Scale bars: 1 μm.

Author contributions

U. Tillmann: original concept, isolation of strains, morphological analysis and discussion, drafting and editing manuscript. A. Beran: isolation of strains, morphological discussion, editing manuscript; M. Gottschling: phylogenetic analysis, drafting and editing manuscript; S. Wietkamp, DNA extraction and sequencing, editing manuscript; M. Hoppenrath: original concept, morphological discussion, drafting and editing manuscript.

Additional information

Funding

This work was supported by the PACES II research program of the Alfred-Wegener-Institute as part of the Helmholtz Foundation initiative in Earth and Environment.