Blastodinium

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Classification

Higher Order Taxa

Domain:Eukaryota; Phylum:Dinoflagellata; Class:Blastodiniphyceae; Order:Blastodiniales; Family:Blastodinidae; Genus:Blastodinium

Genus

Blastodinium

Description and Significance

This genus contains cryptic species. All species in this genus have very similar morphological features, only differing slightly in their genomes. These species are obligate parasites, in which they must live inside a host in order to complete their life cycles. This genus will inhabit the gut of marine copepods, a group of small crustaceans typically 1-2mm in length. These parasites can grow to be a few hundred μm in length while inside the host.

These parasites are found in habits occupied by their copepods hosts-across the globe. However, these parasites are found in greater abundances in low nutrient, oligotrophic marine waters closer to the equator. The parasites found in this habitat have a greater chance of possessing chloroplasts, however, those found in colder waters near the poles of the planet are often found having no chloroplasts.

Life Cycle

The complete life cycle of species in the genus Blastodinium is unknown due to lack of experimental research. The life cycle stages during and after parasitism are known, however. This stage of the life cycle consists of the dinospore of the organism being ingested by the host and it becoming lodged in the copepod's gut. This dinospore grows into a trophocyte while inside the host. The trophocyte then divides into a secondary trophocyte and a gonocyte. The seconary trophocyte can divide into succeeding trophocytes and gonocytes, while the gonocyte will form sporocytes. Through dispersal mechanisms, the sporocytes release sex cells from the host, allowing more copepods to become hosts after the ingestion of spores.

Cell Structure and Metabolism

Ecology and Pathogenesis

The parasitic species in the genus Blastodinium have the ability to reverse the sex of male copepods and cause female copepods to become sterile. It is hypothesized that the size of the parasite inside the host can cause the loss of physiological reproductive function in females due to the pressure on its organs. The sex reversal mechanism that occurs in male copepods remains inconclusive due to lack of research on the subject. These effects on the male and female copepods would have a direct impact on copepod populations. The copepod population would be reduced due to the inability to mate between copepods. This would impact the higher trophic levels. This is just one ecological impact these parasites have.

Another impact is the effect on the biogeochemical cycle. A study completed by the Norwegian Institute of Marine Research completed a study that measured the fecal pellet reproduction rate of infected copepods and uninfected copepods(2). The results showed the rates of uninfected copepods were much higher when producing fecal pellets. This has a negative effect on the biogeochemical cycle because it causes reduced organic material to sink to the bottom of the ocean, where many organisms feed on this material on the ocean floor.

These two previous ecological impacts are due to the pathology of these parasites. However, the fact that Blastodinium do not directly harm their hosts causes some to speculate these species to act as symbionts under certain circumstances. The organisms that exhibit parasitism would often be the ones which cannot perform photosynthesis (the organisms in colder waters). This is due to the organism having to rely on consuming much of its host's energy via food. The photosynthetic Blastodinium are hypothesized to provide their host with certain nutrients, thus being considered symbionts. However, many of these theories have never been tested experimentally and only have validity from natural observations.

References

1.Chatton É. (1920). Les Péridiniens parasites: morphologie, reproduction, ethologie. Arch. Zool. Exp. Gen. 59; 3, 116-117, 121

2. D. M. Fields, J. A. Runge, C. Thompson, S. D. Shema, R. M. Bjelland, C. M. F. Durif, A. B. Skiftesvik, H. I. Browman; Infection of the planktonic copepod Calanus finmarchicus by the parasitic dinoflagellate, Blastodinium spp: effects on grazing, respiration, fecundity and fecal pellet production, Journal of Plankton Research, Volume 37, Issue 1, 1 January 2015, Pages 211–220

Author

Page authored by _____, student of Prof. Jay Lennon at IndianaUniversity.