A Molecular Perspective on Ecological Differentiation and Biogeography of Cyclotrichiid Ciliates

Abstract

Cyclotrichiids are of ecological and evolutionary interest by virtue of their importance in red tide formation, their highly divergent small subunit (SSU) ribosomal RNA (rRNA) genes, kleptoplastidy, and utility as indicators of eutrophication. However, only seven strains have had their SSU rRNA genes sequenced and their environmental diversity and distribution are largely unknown. We probed 67 globally dispersed freshwater column/sediment and soil DNA samples (eDNAs) and constructed 24 environmental gene libraries using polymerase chain reaction primers specific to an uncharacterised cyclotrichiid subgroup. We reveal a novel, globally ubiquitous freshwater clade comprising 25 genetically distinct SSU ribosomal DNA (rDNA) sequences (SSU-types). Some identical SSU-types were detected at globally widely distributed sites. The SSU-types form four distinct phylogenetic clusters according to marine or non-marine provenance, suggesting at least one major marine-freshwater evolutionary transition within the cyclotrichiids. We used the same primers to sample intensively 18 sampling points in 13 closely situated lakes, each characterised by 14 environmental variables, and showed that molecular detection or non-detection of cyclotrichiids was most significantly influenced by levels of total phosphorus, dissolved organic carbon, and chlorophyll a. Within the subset of lakes in which cyclotrichiids were detected, closely related SSU-types differed in their ecological preferences to pH, total phosphorus, and sample depth.

Consistent patterns of high alpha and low beta diversity in tropical parasitic and free‐living protists

“…The dominant group within Cercozoa was the sarcomonads (44.9% of reads, 38.2% of OTUs), which comprises the Cercomonadida and Glissomonadida. These two groups are generally bacterivorous or fungivorous flagellates (Bass et al., ), although one per cent of the glissomonad reads were assigned to an algivorous viridiraptorid genus (Hess & Melkonian, ). Other detected algivorous cercozoans included the vampyrellid amoebae (Berney et al., ).…”

The Genetic Diversity of Mesodinium and Associated Cryptophytes

“…At least one additional major clade of Mesodinium -like ciliates are found in freshwater habitats, and phylogenies based on the SSU rRNA gene group them as a sister group to M. pulex (Bass et al, 2009). Since we did not sequence samples from freshwater habitats and no cultures of these species were available, comparisons of their full rRNA gene cassette to marine Mesodiniidae were not made here.…”

Studies on the Genus Mesodinium II. Ultrastructural and Molecular Investigations of Five Marine Species Help Clarifying the Taxonomy

“…Five freshwater Mesodinium environmental sequences were chosen as outgroup based on Bass et al. (). Six of the marine species were obtained during this study while all others were retrieved from GenBank.…”

“…Crude cultures. Cells of M. chamaeleon were isolated from shallow waters at the sand surface in Niva˚Bay, Denmark during the summers of 2007-2009(Moestrup et al 2012. When offered the cryptophyte Chroomonas vectensis as prey, the crude cultures could be maintained in the laboratory for several months.…”