Heterogeneity of LSU rDNA sequences and morphology of Gymnodinium catenatum dinoflagellate strains in Bahia Concepcion, Gulf of California, Mexico.

We report the large subunit (LSU) rDNA sequences and morphology of several Gymnodinium catenatum dinoflagellate strains isolated from Bahía Concepción, Mexico. PCR amplifications of the D1–D2 fragment of the nuclear LSU rDNA gene resulted in a single product of ∼889 bp. A phylogenetic tree was constructed from the partial LSU rDNA (350 bp) sequences from six strains of G. catenatum isolated from the bay and 12 isolates from around the world. Strains from the bay grouped within the G. catenatum clade; however, a constant characteristic of G. catenatum strains from the bay is that, at position ≈453, a single nucleotide polymorphism was observed, presenting cytosine instead of guanine. This single base polymorphism could indicate a mutation or genetic isolation from other G. catenum populations. It is suggested that the Western Pacific could be the ancestral population of this species. Significant differences were found between cell length (CL), cell width (CW) and CW/CL ratios in laboratory cultures in the late exponential growth phase. Average CL varied between 41 and 53.69 μm, with a range between 26.94 and 69.99 μm; average CW varied between 33.75 and 40.68 μm, with a range between 25.04 and 54.73 μm; the average CW/CL varied between 0.76 and 0.97 μm, with a range between 0.49 and 1.27 μm. Cingulum thickness was between 3 and 4.11 μm, with a range between 1.97 and 6.74 μm. Cell size varied with the length of the chain and position in the chain. [ABSTRACT FROM AUTHOR]