Morphological, genetic and mating diversity within the widespread bioindicator Nitzschia palea (Bacillariophyceae)

Abstract

Trobajo R., Clavero E., Chepurnov V.A., Sabbe K., Mann D.G., Ishihara S. and Cox E.J. 2009. Morphological, genetic and mating diversity within the widespread bioindicator Nitzschia palea (Bacillariophyceae). Phycologia 48: 443–459. DOI: 10.2216/08-69.1.

Nitzschia palea (Kützing) W. Smith is believed to be a widely distributed diatom and is common in various lotic and lentic freshwater habitats. However, it is also taxonomically problematic. As part of a multidisciplinary study of this diatom, 25 clones identified morphologically as N. palea were isolated from different freshwater habitats around the world (Belgium, Brazil, Egypt, India, Japan, Paraguay, Spain, Sri Lanka and the United Kingdom). Morphological and genetic diversity (using the hypervariable D1–D2 domains of LSU rDNA) were investigated, and an almost complete set of interclonal crossing experiments was carried out. Results indicate that N. palea is not a simple, homogeneous taxon and that N. palea will probably have to be split into three or more species. Molecular and mating groups do not separate along the traditional morphological boundaries among N. palea varieties, in particular between vars palea and debilis, two taxa that are commonly used to discriminate between different degrees of water pollution. At least two of the putative species within the N. palea complex appear to be geographically widespread. Because of the complexity of variation revealed by the LSU, mating and morphometric data, it is clear that further work, using extra genetic markers and new isolates, will be needed to determine the full extent of cryptic and pseudocryptic speciation in N. palea and to investigate whether the segregate species are ecologically differentiated and have value as indicators.

Key Words::

• Nitzschia palea
• LSU rDNA
• Diatoms
• Cryptic diversity
• Sexual reproduction
• Morphology

ACKNOWLEDGMENTS

Financial support for this research was provided by the European Commission, Marie Curie Research Fellowship, to Rosa Trobajo at the Natural History Museum, London. Special thanks to Sylvie Cousin for introducing Rosa Trobajo into the molecular techniques. The molecular work and mating experiments were carried out at the Laboratory of Protistology and Aquatic Ecology of Ghent University, Belgium. Many thanks to Mamen Peña (Natural History Museum, UK), Juan Tun-Garrido (Autonomous University, Yucatán, Mexico) and Aitor Laza-Martínez (University of Basque Country, Spain) for collecting samples from Paraguay, Argentina, Egypt, Brazil and northern Spain and to Shigeki Mayama (Tokyo Gakugei University, Japan) for providing N. palea Japan F clone. The support of Ben Williamson and Alex Ball (EMMA Unit, NHM) in using the EM facilities at the Natural History Museum is also gratefully acknowledged. Completion of the manuscript was aided by an EU Synthesys award to Rosa Trobajo to visit Royal Botanic Garden Edinburgh.