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Cryptic species in cyanobacterial systematics: a case study of Phormidium retzii (Oscillatoriales) using RAPD molecular markers and 16S rDNA sequence data
Casamatta, D.A.; Vis, M.L.; Sheath, R.G. (2003). Cryptic species in cyanobacterial systematics: a case study of Phormidium retzii (Oscillatoriales) using RAPD molecular markers and 16S rDNA sequence data. Aquat. Bot. 77(4): 295-309. dx.doi.org/10.1016/j.aquabot.2003.08.005
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    DNA; Genetic diversity; Phylogeny; RNA; Taxonomy; Phormidium retzii Kützing ex Gomont, 1892 [WoRMS]; Fresh water

Authors  Top 
  • Casamatta, D.A., correspondent
  • Vis, M.L.
  • Sheath, R.G.

Abstract
    The genetic variability of the cosmopolitan, ubiquitous freshwater cyanobacterium Phormidium retzii was assessed using random amplified polymorphic DNA (RAPD) markers and nearly complete (ca. 95%) 16S rDNA sequences. Strains consistent with the morphological species circumscription were utilized from geographically distant locations ranging from British Columbia, Canada, in the north to Rio Claro, Costa Rica in the south, and from Rhode Island, USA in the east coast to Washington State, USA on the west coast. In addition, some strains were from geographically close (<35 km apart) locales. To assess biogeographic trends, the nine RAPD primers utilized yielded 133 distinct bands in total from the 12 strains. Non-metric multidimensional scaling (NMDS) analyses revealed that the strains isolated from Ohio, Connecticut, and Rhode Island were closely related with the Costa Rica strain and one Washington State strain associated with this group. The two strains from Canada, British Columbia and Ontario, were closely related and clustered with the two other strains from Washington State. The remaining two strains from Mexico and Missouri were loosely associated with this cluster and genetically distinct. Geographic proximity did not correlate with genetic similarity (Mantel test, r = 0.235,P > 0.05). A 1340 bp region of the 16S rRNA gene was sequenced for 8 of the 12 strains used in the RAPD analysis. Sequence homology among strains ranged from 88.4 to 98.4%, implying the presence of cryptic species within this group of strains. Given the lack of sequence similarity, P. retzii as presently circumscribed most likely represents several cryptic species not clearly distinguishable with light microscopy of morphological features. This conclusion may explain the lack of correlation between geographic proximity and genetic similarity. This research provides further strength for the case of species of cyanobacteria being more localized rather than having global distributions.

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