Pinnularia catenaborealis sp. nov. (Bacillariophyceae), a unique chain-forming diatom species from James Ross Island and Vega Island (Maritime Antarctica)

Abstract:

A recent detailed survey of the Maritime Antarctic diatom flora using a fine-grained taxonomy resulted in the description of many new species of Pinnularia in general and the section Distantes, including the P. borealis species complex, in particular. Moreover, DNA-based studies of P. borealis revealed that many more species need to be described within this complex. During a survey of the freshwater littoral diatom flora of James Ross Island (Ulu Peninsula) and Vega Island in Maritime Antarctica, a previously unknown chain-forming species in the P. borealis species complex of section Distantes was cultured from three different localities. Molecular phylogenies based on the nuclear-encoded D1–D3 large-subunit ribosomal DNA and plastid rbcL genes revealed that all cultures belong to a distinct highly supported lineage within the P. borealis species complex. Pinnularia catenaborealis sp. nov. is characterised by the presence of small spines located on a raised, thin silica ridge that almost entirely surrounds the valve face near the valve face/mantle junction, and the presence of small silica plates near the apices. In culture, P. catenaborealis formed chains of several tens of cells and in oxidised natural material, chains up to seven frustules were observed. Pinnularia catenaborealis is described from the littoral zone of freshwater Black Lake (Ulu Peninsula, James Ross Island) and has also been observed on nearby Vega Island. Although P. borealis is generally regarded as a (semi-)terrestrial diatom complex mainly occurring in (moist) soils and mosses, P. catenaborealis was found in freshwater habitats with an alkaline pH and low conductivity.

Key Words::

• Colony formation
• Cultures
• Molecular phylogeny
• Nuclear-encoded LSU rDNA
• Pinnularia borealis
• rbcL

ACKNOWLEDGEMENTS

Part of this research was financially supported by the Fund for Scientific Research – Flanders (FWO-Flanders, Belgium, funding of EP as a PhD student and PV as a postdoctoral fellow). During her stay in Belgium, EH benefited from a Charles University Mobility grant and the Hlávka Foundation for travel funding. Part of the research was funded within the Belspo CCAMBIO project. The BCCM/DCG culture collection is supported by Belspo. Mr. Jan Kavan is thanked for collecting the Vega Island sample in 2013 and Juan Presta is acknowledged for the Black Lake samples of 2014. The authors also thank all members of the expeditions to the Czech Antarctic Station ‘J.G. Mendel’. The members of the scientific expedition ‘Lagos 2012, 2013 and 2014′ (Picto project nr. 2010-0096) are thanked for their support and help in the field, together with the Instituto Antártico Argentino Dirección Nacional del Antártico for all logistical support during the Antarctic expedition. Sofie D'hondt is thanked for her help with the molecular analysis, Olga Chepurnova and Tine Verstraete for their help with the cryopreservation of the culture material.