Polykrikaceae

The Polykrikaceae (also known as Polykrikidae) are a family of athecate dinoflagellates of the order Gymnodiniales. Members of the family are known as polykrikoids. The family contains two genera: Polykrikos and Pheopolykrikos.[2]

Polykrikaceae
A light micrograph of Polykrikos kofoidii showing an extruded nematocyst. Scale bar = 10µm.[1]
Scientific classification
(unranked):
SAR
(unranked):
Alveolata
Phylum:
Dinoflagellata
Class:
Dinophyceae[2]
Order:
Gymnodiniales
Family:
Polykrikaceae
Genera

Characteristics

The most distinctive feature of polykrikoids is their formation of multinucleate "pseudocolonies" consisting of an even number of subunit zooids. The two genera differ in number of nuclei; possessing two nuclei regardless of the number of zooids is a synapomorphy for Polykrikos, whereas Pheopolykrikos possess equal numbers of nuclei and zooids.[3]

Along with the Warnowiaceae (warnowiids), polykrikoids are known for possessing unusually complex subcellular structures. In particular, an extrusome complex of two organelles called the nematocyst and taeniocyst is considered a synapomorphy for Polykrikos.[1][3] Molecular phylogenetics studies suggest some inconsistency in the taxonomy of this group, particularly in the assignment of species to one of the two genera.[4][5]

Habitat and life cycle

Most polykrikoids are planktonic, although one species - P. lebourae - is benthic.[3] The family includes photosynthetic, heterotrophic, and mixotrophic species.[6] Some species, such as P. kofoidii, are of scientific interest due to their status as predators of other dinoflagellates, a behavior that is significant in the regulation of algal blooms.[6][7][8] Others, such as Ph. hartmanii (which has been reclassified P. hartmanii)[5] are themselves causes of ichthyotoxic algal blooms.[9] P. hartmanii is capable of both heterothallic (outcrossing) and homothallic (self-fertilizing) sexual reproduction.[10]

The reproductive behaviors of polykrikoids are mostly not well understood, although P. kofoidii has been studied and found to have a complex life cycle of both vegetative (asexual) and sexual reproduction complicated by its pseudocolonial structure.[11]

Evolution

The family demonstrates a complex evolutionary history indicating multiple instances of loss of photosynthetic plastids in different lineages.[6] The distinctive pseudocolonial structure may have arisen in multiple evolutionary lineages from ancestors capable of forming chains of distinct individual cells.[3]

References
  1. Hoppenrath, M; Bachvaroff, TR; Handy, SM; Delwiche, CF; Leander, BS (25 May 2009). "Molecular phylogeny of ocelloid-bearing dinoflagellates (Warnowiaceae) as inferred from SSU and LSU rDNA sequences". BMC Evolutionary Biology. 9: 116. doi:10.1186/1471-2148-9-116. PMC 2694157. PMID 19467154.
  2. Michael D. Guiry (2015). Guiry MD, Guiry GM (eds.). "Polykrikaceae Kofoid & Swezy, 1921". AlgaeBase. National University of Ireland, Galway. World Register of Marine Species. Retrieved 8 August 2015.
  3. Hoppenrath, Mona; Leander, Brian S. (April 2007). "Character Evolution in Polykrikoid Dinoflagellates". Journal of Phycology. 43 (2): 366–377. doi:10.1111/j.1529-8817.2007.00319.x.
  4. Reñé, Albert; Camp, Jordi; Garcés, Esther (May 2015). "Diversity and Phylogeny of Gymnodiniales (Dinophyceae) from the NW Mediterranean Sea Revealed by a Morphological and Molecular Approach". Protist. 166 (2): 234–263. doi:10.1016/j.protis.2015.03.001. hdl:10261/116250. PMID 25847865.
  5. Hoppenrath, Mona; Yubuki, Naoji; Bachvaroff, Tsvetan R.; Leander, Brian S. (January 2010). "Re-classification of Pheopolykrikos hartmannii as Polykrikos (Dinophyceae) based partly on the ultrastructure of complex extrusomes". European Journal of Protistology. 46 (1): 29–37. doi:10.1016/j.ejop.2009.08.003. PMID 19767184.
  6. Gavelis, Gregory S.; White, Richard A.; Suttle, Curtis A.; Keeling, Patrick J.; Leander, Brian S. (17 July 2015). "Single-cell transcriptomics using spliced leader PCR: Evidence for multiple losses of photosynthesis in polykrikoid dinoflagellates". BMC Genomics. 16 (1): 528. doi:10.1186/s12864-015-1636-8. PMC 4504456. PMID 26183220.
  7. Matsuyama, Y; Miyamoto, M; Kotani, Y (1999). "Grazing impacts of the heterotrophic dinoflagellate Polykrikos kofoidii on a bloom of Gymnodinium catenatum" (PDF). Aquatic Microbial Ecology. 17: 91–98. doi:10.3354/ame017091.
  8. JEONG, HAE JIN; KIM, SOO KYEONG; KIM, JAE SEONG; KIM, SEONG TAEK; YOO, YEONG DU; YOON, JOO YIH (May 2001). "Growth and Grazing Rates of the Heterotrophic Dinoflagellate Polykrikos kofoidii on Red-Tide and Toxic Dinoflagellates". The Journal of Eukaryotic Microbiology. 48 (3): 298–308. doi:10.1111/j.1550-7408.2001.tb00318.x. PMID 11411838.
  9. Tang, Ying Zhong; Harke, Matthew J.; Gobler, Christopher J.; Cock, M. (December 2013). "Morphology, phylogeny, dynamics, and ichthyotoxicity of (Dinophyceae) isolates and blooms from New York, USA". Journal of Phycology. 49 (6): 1084–1094. doi:10.1111/jpy.12114.
  10. Z Chai, Z Hu, Y Liu, Y Tang 2020. Proof of homothally of Pheopolykrikos hartmannii and details of cyst germination process Journal of Oceanology and Limnology 38 (1), 114-123
  11. Tillmann, Urban; Hoppenrath, Mona (April 2013). "Life Cycle of the pseudocolonial dinoflagellate (Gymnodiniales, Dinoflagellata)". Journal of Phycology. 49 (2): 298–317. doi:10.1111/jpy.12037. PMID 27008517.
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