Life History of a Marine Dinoflagellate Pyrophacus steinii (Schiller) Wall et Dale

Abstract

The life history of a marine dinoflagellate Pyrophacus steinii (Schiller) Wall et Dale was investigated using clonal cultures isolated from Tokyo Bay. The asexual reproduction is binary fission of the eleutheroschisis type. All processes of asexual and sexual cell division occur inside the theca of the mother cells. Sexual reproduction is anisogamous and heterothallic. Male gametes differ from female gametes and vegetative cells in size, shape and plate tabulation. The female gametes can not be differentiated from the vegetative cells. Cell fusion between the male and female gametes occurs within a few hours to several days after inoculation of the male gametes into a culture of a non-male clone. Zygotes are similar to the vegetative cells in shape except possessing two longitudinal flagella. One to two days after plasmogamy, the zygotes become non-motile, and their protoplasts contract. Within 1 to 3 days, following the condensation of protoplast, they transform to hypnozygotes (resting cysts). The specific features of the life cycle can be summerized as: i) the asexual reproduction is eleutheroschisis, ii) sexual fusion occurs after inoculation of the small round thecate cells, which are equivalent to male gametes, into a culture of a non-male clone, iii) male gametes are distinctive from vegetative cells in their smaller size, round shape, fewer plate number and pale chloroplasts, iv) female gametes can not be differentiated from the vegetative cells, v) the sexual life cycle is anisogamous and heterothallic.

Fragilidium duplocampanaeforme sp. nov. (Dinophyceae): A new phagotrophic dinoflagellate from the French Atlantic coast

“…22). This plate has its homologue in the genus Alexandrium (Fukuyo 1985) but also in Pyrophacus with P. steinii (Figure 3 in Pholpunthin et al 1999) and P. horologium (our observations). The apical pore (a.p.)…”

“…Concerning the small form, a ventral plate fused with the APC has also been reported fromone individual of F. heterolobum (Balech 1959). Since individuals smaller than vegetative cells have already been observed in cultures of Pyrophacus and have been interpreted as gametes (Montresor and Marino 1994;Pholpunthin et al 1999), we hypothesize that these small specimens of F. duplocampanaeforme could be a sign of sexual reproduction in natural conditions, but this still needs to be verified.…”

Taxonomy of Pfiesteria (Dinophyceae)

“…Considerable variability in plate number is known, as well, for some species from field samples and from clonal cultures: vegetative cells and -(-female‖) gametes of Pyrophacus steinii from the same clone have 6-8 apical plates, 10-13 precingular plates, 12 cingular plates, 11-13 postcingular plates, and 3 posterior intercalary plates. In contrast, +(-male‖) gametes have 6 apical plates, 8-9 precingular plates, 8-9 cingular plates, 9 postcingular plates, and 2 posterior intercalary plates (Pholpunthin et al, 1999). In addition, in clonal cultures, the number (e.g.…”

Phylogenetic Relationships among Diverse Dinoflagellate Species Occurring in Coastal Waters off Korea Inferred from Large Subunit Ribosomal DNA Sequence Data

“…Fensome et al (1993) included the somewhat atypical, extremely multiplated Pyrophacus Stein in the Goniodomineae based on a number of homologous features such as the cyst shape, the first apical plate (1'), the APC, and the antapical plate patterns. In addition the occurrence of a small thecate gamete with a reduced number of thecal plates has been reported during a part of the life cycle of Pyrophacus species (Montresor and Marino 1994;Pholpunthin et al 1999). Thus, the familial assignment of P. steinii is well supported by morphological and molecular data.…”