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Variability and species discrimination within the Protogonyaulax tamarensis/catenells species complex : toxic red-tide dinoflagellates Cembella, Allan Douglas


Thecate gonyaulacoid dinoflagellates referable to the genus Protogonyaulax Taylor cause paralytic shellfish poisoning (PSP) in coastal regions throughout the world. Isolates of the Protogonyaulax tamarensis/ catenella species complex from diverse geographical regions, including ten contemporaneous isolates from the same location, were subjected to chemotaxonomic analysis of soluble isozymes by gel electrophoresis, an analysis of toxin components using high-pressure (performance) liquid chromatography and quantitative nuclear DNA determinations by epifluorescence microphotometry. The results were compared with conventional morphological criteria used to discriminate among species, to establish taxonomic linkages and to estimate phenotypic and genotypic variation within this group. These biochemical methods, along with measurements of acclimated growth rate, offered a means of distinguishing between isolates of this species complex, for which the thecal plate patterns were substantially the same. The isozyme patterns revealed a high degree of genetic polymorphism within and among morphotypes and geographical populations. Yet, within the tamarensoid morphotype, isolates from the same location were more similar than to those from elsewhere. This general trend was supported by evidence from toxin profiles and DNA analysis, although toxin heterogeneity was a more conservative measure of variation than isozyme diversity. Protogonyaulax isolates varied markedly in total toxin concentration and toxicity, even through the culture cycle of individual isolates, but the toxin ratios were distinctive and relatively constant. The catenelloid and tamarensoid forms, the dominant morphotypes within this species complex, were not well correlated with the biochemical characters investigated. Given the occasional presence of morphological intermediates, the morphological features presently used to identify P. catenella and P. tamarensis cannot always be used to reliably discriminate between these morphospecies, and appear to be inadequate as stable species descriptors. At least two smaller isolates from allopatric populations exhibited morphological and biochemical differences large enough to indicate possible species divergence. The high level of genetic diversity reflected in the biochemical heterogeneity within populations from a given geographical area suggests that sibling species may also have arisen within sympatrically distributed Protogonyaulax populations.

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