Alveolate

Source: Wikipedia, the free encyclopedia.

Alveolate
Temporal range: EdiacaranRecent[1]
Ceratium furca
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade:
TSAR
Clade: SAR
Clade: Alveolata
Cavalier-Smith, 1991
Phyla
Synonyms
  • Alveolatobiontes

The alveolates (meaning "pitted like a honeycomb")

Eukarya. They are currently grouped with the stramenopiles and Rhizaria among the protists with tubulocristate mitochondria into the SAR supergroup
.

Characteristics

The most notable shared characteristic is the presence of

photosynthetic
organisms.

Transmission electron micrograph of a thin section of the surface of the ciliate Paramecium putrinum, showing the alveoli (red arrows) under the cell surface

Almost all sequenced mitochondrial genomes of ciliates and apicomplexa are linear.

mtDNA of their own but with greatly reduced genome sizes. Exceptions are Cryptosporidium which are left with only a mitosome; ciliates; and Janouškovec et al 2013 demonstrated that Acavomonas diverged early and thus have retained some gene-encoding mtDNA.[6] The mitochondrial genome of Babesia microti is circular.[7] This species is also now known not to belong to either of the genera Babesia or Theileria
and a new genus will have to be created for it.

History

The relationship of apicomplexa, dinoflagellates and ciliates had been suggested during the 1980s, and this was confirmed in the early 1990s by comparisons of ribosomal RNA sequences, most notably by Gajadhar et al.

paraphyletic assemblage. Many biologists prefer the use of the colloquial name 'alveolate'.[10]

Classification

Alveolata include around nine major and minor groups. They are diverse in form, and are known to be related by various ultrastructural and genetic similarities:[11]

The Acavomonidia and Colponemidia were previously grouped together as colponemids, a taxon now split because each has a distinctive organization or ultrastructural identity. The Acavomonidia are closer to the dinoflagellate/perkinsid group than the Colponemidia are.[11] As such, the informal term "colponemids", as it stands currently, covers two non-sister groups within Alveolata: the Acavomonidia and the Colponemidia.[11]

The Apicomplexa and dinoflagellates may be more closely related to each other than to the ciliates. Both have

Amoebophrya, which was classified until now in the Syndiniales
dinoflagellate order.

Some studies suggested the haplosporids, mostly parasites of marine invertebrates, might belong here, but they lack alveoli and are now placed among the Cercozoa.

The ellobiopsids are of uncertain relation within the alveolates. Silberman et al 2004 establish that the

phylogenetic analysis, however as of 2016 no more certainty exists on their place.[15][16]

Phylogeny

In 2017, Thomas Cavalier-Smith described the phylogeny of the Alveolata as follows:[17]

Alveolata
Ciliophora
Intramacronucleata

Heterotrichea

Karyorelictea

Postciliodesmatophora

Desmata

Spirotrichia

Miozoa

Colponemea

Acavomonadia

Acavomonadea

Myzozoa
Apicomplexa

Apicomonada

Sporozoa

Dinozoa

Dinoflagellata

Perkinsea

Taxonomy

Alveolata Cavalier-Smith 1991 [Alveolatobiontes]

  • Phylum
    Ciliophora
    Doflein 1901 stat. n. Copeland 1956 [Ciliata Perty 1852; Infusoria Bütschli 1887; Ciliae, Ciliozoa, Cytoidea, Eozoa, Heterocaryota, Heterokaryota]
  • Phylum
    Miozoa
    Cavalier-Smith 1987
    • Subphylum Colponemidia Tikhonenkov, Mylnikov & Keeling 2013
    • Subphylum Acavomonadia Tikhonenkov et al. 2014
    • Subphylum Myzozoa Cavalier-Smith 2004
      • Infraphylum Apicomplexa Levine 1970 emend. Adl et al. 2005
        • Order ?Vitrellida Cavalier-Smith 2017
        • Class ?Myzomonadea Cavalier-Smith & Chao 2004 sensu Ruggiero et al. 2015
        • Class
          Chromerea
        • Order
          Colpodellida
          Patterson & Zölffel 1991 [Spiromonadida Krylov & Mylnikov 1986]
        • Superclass
          Sporozoa
          Leuckart 1879 stat. nov. Cavalier-Smith 2013 [Gamontozoa]
          • Class
            Blastogregarinida
            Chatton & Villeneuve 1936 [Blastogregarinina; Blastogregarinorina Chatton & Villeneuve 1936]
          • Class
            Paragregarea
            Cavalier-Smith 2014
          • Class
            Gregarinomorphea
            Grassé 1953
          • Class
            Coccidiomorphea
            Doflein 1901
      • Infraphylum Dinozoa Cavalier-Smith 1981 emend. 2003
        • Order ?Acrocoelida Cavalier-Smith & Chao 2004
        • Order ?Rastromonadida Cavalier-Smith & Chao 2004
        • Class Squirmidea Norén 1999 stat. nov. Cavalier-Smith 2014
        • Superclass Perkinsozoa Norén et al. 1999 s.s.
          • Class Perkinsea Levine 1978 [Perkinsasida Levine 1978]
        • Superclass
          Dinoflagellata
          Butschli 1885 stat. nov. Cavalier-Smith 1999 sensu Cavalier-Smith 2013 [Dinozoa Cavalier-Smith 1981]
          • Class Pronoctilucea
          • Class Ellobiopsea Cavalier-Smith 1993 [Ellobiophyceae Loeblich III 1970; Ellobiopsida Whisler 1990]
          • Class Myzodinea Cavalier-Smith 2017
          • Class
            Oxyrrhea
            Cavalier-Smith 1987
          • Class
            Syndinea
            Chatton 1920 s.l. [Syndiniophyceae Loeblich III 1970 s.s.; Syndina Cavalier-Smith]
          • Class Endodinea Cavalier-Smith 2017
          • Class Noctiluciphyceae Fensome et al. 1993 [Noctilucae Haeckel 1866; Noctilucea Haeckel 1866 stat. nov.; Cystoflagellata Haeckel 1873 stat. nov. Butschli 1887]
          • Class Dinophyceae Pascher 1914 [Peridinea Ehrenberg 1830 stat. nov. Wettstein]

Development

The development of plastids among the alveolates is intriguing. Cavalier-Smith proposed the alveolates developed from a chloroplast-containing ancestor, which also gave rise to the

heterokont algae acquired their plastids from a red alga with evidence of a common origin of this organelle in all these four clades.[18]

Evolution

A Bayesian estimate places the evolution of the alveolate group at ~850 million years ago.

Ciliates
, and Colponemids. In other words, the term Myzozoa, meaning "to siphon the contents from prey", may be applied informally to the common ancestor of the subset of alveolates that are neither ciliates nor colponemids. Predation upon algae is an important driver in alveolate evolution, as it can provide sources for endosymbiosis of novel plastids. The term Myzozoa is therefore a handy concept for tracking the history of the alveolate phylum.

The ancestors of the alveolate group may have been photosynthetic.

red alga,[18]
and so it seems likely that the common ancestor of alveolates and heterokonts was also photosynthetic.

In one school of thought the common ancestor of the

rhoptries, micronemes, a polar ring and a coiled open sided conoid.[22] While the common ancestor of alveolates may also have possessed some of these characteristics, it has been argued that Myzocytosis was not one of these characteristics, as ciliates ingest prey by a different mechanism.[11]

An ongoing debate concerns the number of membranes surrounding the plastid across apicomplexans and certain dinoflagellates, and the origin of these membranes. This ultrastructural character can be used to group organisms and if the character is in common, it can imply that phyla had a common photosynthetic ancestor. On the basis that apicomplexans possess a plastid surrounded by four membranes, and that peridinin dinoflagellates possess a plastid surrounded by three membranes, Petersen et al.

endosymbiosis
.

Ciliates are a model alveolate, having been genetically studied in great depth over the longest period of any alveolate lineage. They are unusual among eukaryotes in that reproduction involves a micronucleus and a macronucleus. Their reproduction is easily studied in the lab, and made them a model eukaryote historically. Being entirely predatory and lacking any remnant plastid, their development as a phylum illustrates how predation and autotrophy[20] are in dynamic balance and that the balance can swing one way or other at the point of origin of a new phylum from mixotrophic ancestors, causing one ability to be lost.

Epigenetics

Few

algae have been studied for epigenetics.[24] Those for which epigenetic data are available include some algal alveolates.[24]

References

  1. ^ Li, C.-W.; et al. (2007). "Ciliated protozoans from the Precambrian Doushantuo Formation, Wengan, South China". Geological Society, London, Special Publications. 286 (1): 151–6.
    S2CID 129584945
    .
  2. ^ "alveolate". Memidex (WordNet) Dictionary/Thesaurus. Archived from the original on 2016-04-11. Retrieved 2011-01-26.
  3. PMID 23020233
    .
  4. .
  5. .
  6. .
  7. .
  8. ^ Gajadhar, A. A.; et al. (1991). "Ribosomal RNA sequences of Sarcocystis muris, Theilera annulata, and Crypthecodinium cohnii reveal evolutionary relationships among apicomplexans, dinoflagellates, and ciliates". Molecular and Biochemical Parasitology. 45 (1): 147–153.
    PMID 1904987
    .
    .
  9. .
  10. ^ Kumar, S. & Rzhetsky, A. 1996. Evolutionary relationships of eukaryotic kingdoms. Journal of Molecular Evolution, 42: 183–193
  11. ^
    PMID 24740116
    .
  12. .
  13. .
  14. .
  15. .
  16. .
  17. .
  18. ^ .
  19. .
  20. ^ .
  21. .
  22. .
  23. .
  24. ^ .

External links