Cryptic species in cyanobacterial systematics: a case study of Phormidium retzii (Oscillatoriales) using RAPD molecular markers and 16S rDNA sequence data

• Published in: Aquatic botany 2003, Vol.77 (4), p.295-309
• Main Authors: Casamatta, D.A, Vis, M.L, Sheath, R.G
• Format: Article
• Language: English
• Subjects: Cryptic species; Cyanobacteria; Freshwater; Phormidium retzii; Phylogeny; RAPD; rDNA
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/j.aquabot.2003.08.005

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 (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.