Mating-type determination, gametic recognition and reproductive success in Alexandrium excavatum (Gonyaulacales, Dinophyta), a toxic red-tide dinoflagellate

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Abstract
The phenomena of gametic recognition and efficiency of sexual reproduction were studied in toxigenic isolates of the marine dinoflagellate Alexandrium excavatum (Braarud) Balech (Dinophyta). Crossing experiments between clonal isolates were conducted in order to determine mating-type affiliations and the frequency of successful zygote germination. The frequency of gametic recognition was not clearly linked to the proximity of the geographical origin of isolates, nor was there a significant relationship between the frequency of gametic recognition and the rate of zygote germination. There was a tendency for gametic recognition incompatibility among clonal isolates to relax somewhat with time in culture. These observations can best be interpreted in terms of a polar complementarity model, with active gametic recognition sites at the cell surface. In many basic features, sexual reproduction in this dinoflagellate resembles that observed in certain species of ciliates and foraminifera.