IDENTIFICATION OF GROUP-SPECIFIC AND STRAIN-SPECIFIC GENETIC-MARKERS FOR GLOBALLY DISTRIBUTED ALEXANDRIUM (DINOPHYCEAE) .1. RFLP ANALYSIS OF SSU RIBOSOMAL-RNA GENES

Two distinct small-subunit ribosomal RNA genes (SSU rDNAs), termed the ''A gene'' and ''B gene,'' were recently Sound in the toxic dinoflagellate Alexandrium fundyense Balech. A restriction fragment length polymorphism (RFLP) assay was developed to rapidly detect the A and B genetic markers. SSU rDNA from 58 cultures with species designations of A. tamarense (Lebour) Balech, A. catenella (Whedon et Kofoid) Balech, A. fundyense, A. affine (Fukuyo et Inoue) Balech, A, minutum Halim, A. lusitanicum Balech, and A. andersoni Balech were screened. These cultures represent toxic and nontoxic isolates from North America, western Europe, Thailand, Japan, Australia, and the ballast water of several cargo ships. The RFLP assay revealed five distinct groups. Three subdivided the A. tamarense/catenella/fundyense ''species complex'' into clusters defined by geographic origin, not by morphospecies designations. The fourth group consisted of A. affine, whereas the fifth group was represented by A. minutum, A. lusitanicum, and A. andersoni. The B gene was only found in A. tamarense, A. catenella, and A. fundyense, but not in all isolates. However, all North American isolates of this closely related group harbored this gene, and it also was found in some A. tamarense from scattered locations in Japan and in the ballast water of one ship that operated exclusively between Japan and Australia, Isolates without the B gene appeared to have only a single class of SSU rDNA. The B sequence was not essential for toxin production, but thus Sar those organisms harboring it were toxic. The A. tamarense/catenella/fundyense complex is composed of genetically distinct populations, within which may exist two or all three of the mophotypically defined species. The B gene is a promising taxonomic and biogeographic marker and may be useful for tracking the regional and/or global dispersal of particular populations.