Morphology, phylogeny, and sexual cycle of Pseudo-nitzschia mannii sp. nov. (Bacillariophyceae): a pseudo-cryptic species within the P. pseudodelicatissima complex

Abstract

A. Amato and M. Montresor. 2008. Morphology, phylogeny, and sexual cycle of Pseudo-nitzschia mannii sp. nov. (Bacillariophyceae): a pseudo-cryptic species within the P. pseudodelicatissima complex. Phycologia 47: 487–497. DOI: 10.2216/07-92.1

There is increasing evidence that cryptic and pseudo-cryptic species are widespread in several diatom taxa. This is the case with the genus Pseudo-nitzschia, which includes chain-forming pennate diatoms that bloom both in coastal and open ocean waters. In the last years, up to 10 new species have been described on the basis of morphological and molecular investigations, and some of them are only distinguishable on the basis of minute ultrastructural features of their siliceous frustule. We here describe the morphology of the vegetative cell and sexual stages of Pseudo-nitzschia mannii sp. nov., and present an ITS2-based phylogeny to illustrate genetic relationships between P. mannii sp. nov. and the closest congeneric species. On the basis of ribosomal and chloroplastidial gene phylogenies, P. mannii is closely related to P. calliantha, from which it can be differentiated by its slightly wider cells and a different arrangement of the poroid sectors. The analysed strains did not produce the ASP-toxin domoic acid.

Key Words::

• cryptic species
• diatoms
• ITS rDNA
• morphology
• phylogeny
• pseudo-cryptic diversity
• Pseudo-nitzschia
• Pseudo-nitzschia mannii
• sexual reproduction

ACKNOWLEDGMENTS

This work is part of the PhD programme of A.A. [Open University, London, UK; Stazione Zoologica Anton Dohrn (SZN), Napoli, Italy]. The authors thank David G. Mann (Royal Botanic Garden, Edinburgh, UK) for helpful discussions; Wiebe H.C.F. Kooistra (SZN) for advice on phylogenetic analyses; Raffaele Siano (SZN) for cluster analyses; Bernd Krock (Alfred-Wegener Institute for Polar and Marine Research, Bremerhaven, Germany) for toxin analyses; and Marta Maria Giannone for the Latin translation of the species diagnosis. This study was carried out in the frame of the MarBEF Network of Excellence ‘Marine Biodiversity and Ecosystem Functioning’ (contract no. GOCE-CT-2003-505446) and was partly supported by the Project SEED (Life cycle transformations among HAB species, and the environmental and physiological factors that regulate them) GOCE-CT-2005-003875, both funded in the EU Sixth Framework Programme.