Identity and speciation in marine benthic cyanobacteria: The <I>Phormidium</I>-complex

Abstract

Recent advances in nucleic acid sequencing have confirmed polyphyletic origins of coccoid (Synechocwcus) as well as filamentous (Leptolyngbya) cyanobacteria of simple morphology, whereas genotypic and phenotypic clustering of complex heterocystous forms consistently revealed monphyletic origins. The majority of cyanobacterial morphotypes, however, are between these two extremes, thus requiring a broader comparative ecological, genotypic and phenotypic assessments for satisfactory resolution. Genotypic analyses of cyanobacterial diversity have to date identified extreme environments, such as hypersaline and hydrothermal ones as separate speciation centers. The present work identifies niche differentiation and speciation centers in ecologically optimal environments under stable tropical normal marine conditions. Morphotypic and genotypic properties of a group of non-heterocystous filamentous cyanobacteria associated with benthic bio-sedimentary structures in the lagoons of tropical atolls and islands were compared, including their inter- and intrapopulational size variability. Genotypic distinctions within the studied group of taxa support their separation in smaller genera. The speciation within these genera is reflected in separation by ecological niches as well as in the morphology of their cells and colonies. Morphometric analysis of particular natural populations reveals further a considerable interclonal variability, which statistically supports a separation in sub-specific microtaxa. and reveals the existence of continuing speciation process in the habitat.