Nitzschia captiva sp. nov. (Bacillariophyta), the essential prey diatom of the kleptoplastic dinoflagellate Durinskia capensis, compared with N. agnita, N. kuetzingioides and other species

ABSTRACT

Durinskia capensis is a kleptoplastic dinoflagellate species from high intertidal marine rock pools, which can use a variety of diatoms for photosynthesis. However, very few of the diatoms permit indefinite survival of the dinoflagellate and rbcL sequences show that D. capensis isolated from nature contains one of two closely related Nitzschia species as its kleptoplastids. In culture, without a supply of these ‘essential’ Nitzschia cells to replenish the intracellular store of diatom plastids and other organelles, D. capensis eventually loses all its kleptoplastids and dies. Inside Durinskia, diatoms do not possess frustules and so cannot be compared morphologically with free-living forms. Recently, one of the essential Nitzschia species was isolated from the type locality of D. capensis and grown in culture, allowing comparison with similar Nitzschia species, particularly N. agnita and N. kuetzingioides, examined from type material. We conclude that the ‘essential diatom’ of D. capensis differs morphologically from these and other Nitzschia species and it is therefore described as N. captiva sp. nov. Nitzschia agnita and N. kuetzingioides, on the other hand, are conspecific and N. agnita has priority. Nitzschia captiva and N. agnita are extremely similar in valve shape, dimensions, pattern and ultrastructure, but can be separated by their girdle structure. Nitzschia agnita appears to be a freshwater species, though somewhat salt-tolerant. In contrast, N. captiva, which is known principally from records of the kleptoplastids of D. capensis rather than from frustules, is so far marine.

KEYWORDS:

• Dinotom
• Dinoflagellates
• Endosymbionts
• Kleptoplastids
• Taxonomy

ACKNOWLEDGEMENTS

We are very grateful to Dr Lena Eggers for finding and sending type material of N. agnita and N. kuetzingioides from the Hustedt Collection (Alfred Wegener Institute, Bremerhaven, Germany); the late Dr Luc Ector for help with diatom literature; Frieda Christie, Ruth Hollands and Dr Kanae Nishii for support of the SEM and LM facilities at the Royal Botanic Garden Edinburgh; Sam Bolton for technical assistance; and two anonymous reviewers for constructive comments.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00318884.2023.2169024

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

Additional information

Funding

Initial support for our work was provided by the project ‘Biodiversity and evolution of algae in the Indo-Pacific: a Japan/South Africa comparison’ (Strategic International Research Cooperative Program to J.J. Bolton) of JST in Japan and NRF in South Africa. The establishment of the N. captiva strain was then financially supported by a Bridging Stipend of University of Konstanz (No.638/20, to N. Yamada), and a DFG Research Grant (No. YA 577/2-1, to N. Yamada). We also acknowledge support from the CERCA Programme, Generalitat de Catalunya. The Royal Botanic Garden Edinburgh is supported by the Scottish Government’s Rural and Environment Science and Analytical Services Division.