Electrophoretic analysis of the species and population structure of the diatom Asterionella formosa

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Abstract
One hundred and one clones from 25 North American and 7 European populations of Asterionella formosa Hass. were isolated or obtained from other investigators. Twenty populations were represented by two or more isolates obtained either simultaneously or at different times of the year.Soluble proteins, present in crude extracts of homogenized cells from batch cultures of each isolate, were separated in polyacrylamide gels and stained either with a nonspecific protein stain or for enzyme activity. Six enzymes (leucine aminopeptidase, alkaline phosphatase, glutamate dehydrogenase, malate dehydrogenase, acid phosphatase, and esterase) were examined but only the latter three, together with general protein, showed variation in electrophoretic banding patterns.There was no detectable variation (with one possible exception) among multiple isolates from the same population, suggesting that the populations are clonal or at least highly homogeneous genetically. This was true both for contemporaneous isolates and for isolates obtained at different times of the year and in different years.On the other hand, isolates from different populations differ by 3 to 28 bands out of 41. The frequency distribution of a measure of dissimilarity between pairs of population-specific electrophoretic patterns is unimodal, indicating that the observed variation is essentially continuous and that the collection of isolates is not comprised of a small number of discrete races. However, identification of groups of populations by means of hierarchical cluster analysis in terms of their geographical origin and of the ecological characteristics of their habitat was possible to a limited extent.