Evolution of different life-cycle strategies in oceanic calcareous dinoflagellates

The formation of non-motile resting cysts within the dinoflagellate life-cycle has long been considered to be unsuitable for open oceanic environments, because a considerable part of a population might be lost due to sinking. An alternative life-cycle with the production of vegetative calcareous cells as the dominant life-cycle stage was reported for the oceanic calcareous dinoflagellate Thoracosphaera heimii, and earlier observations suggested that other oceanic calcareous dinoflagellates might have similar life-cycles. In order to test this hypothesis, we investigated the life-cycle of three oceanic calcareous dinoflagellates, Thoracosphaera heimii, Leonella granifera and Calciodinellum levantinum in culture and determined relative ploidy levels with confocal laser scanning microscopy. Whereas C. levantinum forms calcareous resting cysts within the diploid sexual life-cycle phase, T. heimii and L. granifera form vegetative calcareous cells within the haploid asexual phase. By comparison with recently pu...