Ploidy analysis of the two motile forms of Chrysochromulina polylepis (Prymnesiophyceae)

In some cultures of the flagellate Chrysochromulina polylepis Manton et Parke, established from cells isolated from the massive bloom in Skagerrak and Kattegat in 1988, we observed two motile cell types. They were termed authentic and alternate cells and differed with respect to scale morphology. To investigate whether or not the two cell forms were joined in a sexual life cycle, the relative DNA content per cell and relative size of cells of several clonal cultures of C. polylepis were determined by flow cytometry. Percentages of authentic and alternate cells in the cultures were estimated by transmission electron microscopy. Pure authentic cultures (alpha) contained cells with the lowest level of DNA and were termed haploid. Two pure alternate cultures (beta) contained cells with double the DIVA content of authentic cells and were termed diploid. Other pure alternate cultures contained haploid cells only, of both haploid and diploid cells. Three cell types were observed, each capable of vegetative propagation: authentic haploid, alternate haploid, and alternate diploid cells. Both the haploid and diploid alternate cells were larger than the haploid authentic cells. Cultures containing diploid cells appeared unstable: cell type ratio and ploidy ratio changed during the experiment where this cell type was present, particularly when grown in continuous light. In contrast, cultures with only haploid cells remained unchanged at all growth conditions tested. Light condition may influence cell type ratio and ploidy ratio. Our attempt to induce syngamy by mixing different authentic haploid clones did not result in mating. Assuming that the authentic and alternate cell types are of the same species, the life cycle of C. polylepis Includes three flagellated scale-covered cell forms. Two of the cell types are haploid and may function as gametes, and the third is diploid, possibly being the result of syngamy.