The life history of the toxic marine dinoflagellate Protoceratium reticulatum (Gonyaulacales) in culture |
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| Institution: | 1. Department of Earth Sciences, Earth Sciences Centre, University of Toronto, 22 Russell St., Toronto, Ontario M5S 3B1, Canada;2. Research Unit for Palaeontology, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium;3. Department of Earth Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, Ontario L2S 3A1, Canada;1. GEOTOP, Université du Québec à Montréal, P.O. Box 8888, Montréal, Québec H3C 3P8, Canada;2. Département de Géologie et Océanographie, UMR 5805 CNRS, Université Bordeaux 1, avenue de Facultés, 33405 Talence cedex, France;3. School of Environmental Sciences, University of Liverpool, Liverpool L69 7ZT, UK;4. Alfred Wegener Institute for Polar and Marine Research (AWI), 27515 Bremerhaven, Germany;5. Department of Earth Science, Faculty of Geosciences, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, The Netherlands |
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| Abstract: | Asexual and sexual life cycle events were studied in cultures of the toxic marine dinoflagellate Protoceratium reticulatum. Asexual division by desmoschisis was characterized morphologically and changes in DNA content were analyzed by flow cytometry. The results indicated that haploid cells with a C DNA content occurred only during the light period whereas a shift from a C to a 2C DNA content (indicative of S phase) took place only during darkness. The sexual life cycle was documented by examining the mating type as well as the morphology of the sexual stages and nuclei. Gamete fusion resulted in a planozygote with two longitudinal flagella, but longitudinally biflagellated cells arising from planozygote division were also observed, so one of the daughter cells retained two longitudinal flagella while the other daughter cell lacked them. Presumed planozygotes (identified by their longitudinally biflagellated form) followed two life-cycle routes: division and encystment (resting cyst formation). Both the division of longitudinally biflagellated cells and resting cyst formation are morphologically described herein. Resting cyst formation through sexual reproduction was observed in 6.1% of crosses and followed a complex heterothallic pattern. Clonal strains underwent sexuality (homothallism for planozygote formation and division) but without the production of resting cysts. Ornamental processes of resting cysts formed from the cyst wall under an outer balloon-shaped membrane and were fully developed in <1 h. Obligatory dormancy period was of ～4 months. Excystment resulted in a large, rounded, pigmented, longitudinally biflagellated but motionless, thecate germling that divided by desmoschisis. Like the planozygote, the first division of the germling yielded one longitudinally biflagellated daughter cell and another without longitudinal flagella. The longitudinal biflagellation state of both sexual stages and of the first division products of these cells is discussed. |
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| Keywords: | Life history Longitudinal biflagellation Sexual cycle Planozygote and germling division Resting cyst |
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