A NOVEL ASSOCIATION BETWEEN AN ENDEMIC STICKLEBACK AND A PARASITIC DINOFLAGELLATE. 2. MORPHOLOGY AND LIFE CYCLE¹

Abstract

An unusual dinoflagellate has been discovered in association with an endemic population of stickleback, Gasterosteus (L.), from the Queen Charlotte Islands, Canada. The dinoflagellate spends most of its life cycle as a coccoid vegetative cyst, not as a parasitic trophont. The vegetative cyst is unique in containing a rigid fenestrated matrix, which is penetrated by cytoplasmic process that emanate from a central area containing the dinokaryotic nucleus and associated chloroplasts. Some pores in the matrix are filled by oil droplets or starch granules. Intracellular bacteria are found throughout the cyst, sometimes in association with the nucleus. The cytoplasm contains accumulation bodes, microbodies, polyhedral crystals, chloroplasts and polyvesicular bodes. The encysted dinoflagellate has several potential strategies. It can 1) shed its wall and become amoeboid; 2) undergo sporogenesis and give rise to both regular and resistant spores; 3) divide mitotically, with a gradual reduction in the size of daughter cells down to 20 μm; and 4) apparently form a resting cyst, during which it secretes a thick outer wall composed of five layers. Taxonomically, this unusual dinoflagellate appears to be a new member of the Blastodiniales, although its position will become clearer when details of the motile stage are known.

Species of the toxic Pfiesteria complex, and the importance of functional type in data interpretation.

“…Lobose amoebae of various sizes were also observed in this life cycle (78,79). Overall, Buckland-Nicks and co-workers (77)(78)(79) reported lobose, rhizopodial, and spheroid amoeboid stage, a vegetative dinokaryon, dinospores (zoospores) with condensed chromosomes, and amoeboid resting cyst. The biochemical and ultrastructural mechanisms whereby the dinoflagellate zoospore mesokaryote nucleus with permanently condensed chromosomes can change [in Pfiesteria, sometimes within minutes (7)] to the eukaryote nucleus of amoeboid stages has not been examined in detail.…”

“…Although the nuclear status of the amoeba stage was not ascertained, the nuclei of the multinucleate reproductive cyst from which the mesokaryotic gymnodinioid swarmers emerged were eukaryotic with dispersed chromatin material. In H. ichthyophilum ectoparasite of sticklebacks, Buckland-Nicks et al (77,79) reported that the typical dinokaryon nucleus of the vegetative cyst transformed to a eukaryotic nucleus in the lobose amoebae. From research with the dinoflagellate, O. fritillariae (marine ectoparasite of Appendicularians), Cachon and Cachon (74) reported that the nucleus of young, attached ectoparasites had condensed, rodlike chromosomes similar to those of the free-living gymnodinioid stage.…”

MITOCHONDRIAL DNA INGASTEROSTEUSAND PLEISTOCENE GLACIAL REFUGIUM ON THE QUEEN CHARLOTTE ISLANDS, BRITISH COLUMBIA

“…The population in Rouge Lake, which is monomorphic for the Argonaut haplotype, exhibits some of the most pronounced reduction in spines observed in the species (Reimchen, 1984). As well, it is symbiotic with an unusual taxon of dinoflagellate, an association which appears to have no counterpart elsewhere in the circumboreal distribution of either group (Reimchen and Buckland-Nicks, 1990;Buckland-Nicks et aI., 1990). When these factors are taken in concert with the predicted divergence time derived from mtDNA, an extended pre-glacial history in the Argonaut Plain is suggested.…”

THE LIFE CYCLE AND TOXICITY OF PFIESTERIA PISCICIDA REVISITED1

“…For example, Cystodinedria inermis (Geitler) Pascher, described as having a complex life cycle with amoeboid stages (Pfiester and Popovský 1979, Popovský and Pfiester 1982), was questioned by Coats (2002) because the direct observations had been made from field material (rather than pure cultures—which, however, have not yet been possible for many heterotrophic dinoflagellates). Cultured heterotrophic species also have been reported to have complex life cycles with amoeboid or other active benthic stages in media lacking protozoan contaminants (Buckland‐Nicks et al 1990, 1997, Appleton and Vickerman 1998). Amoeboid or amoeba‐like stages have been observed in ecto‐ and endoparasitic dinoflagellates, and in some mixotrophic predaceous species (Buckland‐Nicks and Reimchen 1995, Buckland‐Nicks et al 1990, 1997, Appleton and Vickerman 1998, Seaborn et al 1999).…”

“…Cultured heterotrophic species also have been reported to have complex life cycles with amoeboid or other active benthic stages in media lacking protozoan contaminants (Buckland‐Nicks et al 1990, 1997, Appleton and Vickerman 1998). Amoeboid or amoeba‐like stages have been observed in ecto‐ and endoparasitic dinoflagellates, and in some mixotrophic predaceous species (Buckland‐Nicks and Reimchen 1995, Buckland‐Nicks et al 1990, 1997, Appleton and Vickerman 1998, Seaborn et al 1999). Litaker et al concluded that “ P. piscicida has a life cycle typical of free‐living marine dinoflagellates.…”