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Astrephomene

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Astrephomene
Scientific classification Edit this classification
Clade: Viridiplantae
Division: Chlorophyta
Class: Chlorophyceae
Order: Chlamydomonadales
Family: Goniaceae
Genus: Astrephomene
Pocock
Species

Astrephomene is a genus of green algae in the family Goniaceae, order Chlamydomonadales.[1][2] The genus was first described in 1937 by Pocock and named by Pockock in 1953 (Stein 1958).

Taxonomy

It was formerly placed in the monotypic family Astrephomenaceae. Astrephomenaceae is now considered obsolete, and Astrephomene is now classified within the Goniaceae.[3]

Description

Astrephomene gubernaculifera is a colonial, flagellated volvocine green algae. It consists of 16, 32, 64 or 128 cells, 2 to 7 of which are small and oriented such that their flagella form a rudder (Stein 1958). Each cell is surrounded by a gelatinous matrix and contains an eyespot, two flagella and 1-3 contractile vacuoles at the anterior end.

Astrephomene gubernaculifera can reproduce sexually or asexually. During asexual reproduction of Astrephomene, rotation of daughter protoplasts occurs in conjunction with the movement of basal bodies during successive cell divisions, ending with the anterior end of all cells of the daughter colony outside after the first nuclear and cytoplasmic division.[4] This type of asexual reproduction is unique among the colonial volvocine green algae (Pocock 1953). By contrast, in Eudorina, protoplast rotation is lacking during successive divisions; a spheroidal colony is formed by means of inversion after successive divisions. Astrephomene gubernaculifera has two mating types that reproduce to form zygotes.

Schematic diagrams of the two mechanisms of spheroidal colony formation in the volvocine algae. In Astrephomene, rotation of daughter protoplasts occurs in conjunction with the movement of basal bodies during successive cell divisions. In Eudorina, protoplast rotation is lacking during successive divisions; a spheroidal colony is formed by means of inversion after successive divisions.

Evolution

Colony inversion is believed to have arisen twice in the order Chlamydomonadales. Spheroidal colony formation differs between the two lineages: rotation of daughter protoplasts during successive cell divisions in Astrephomene, and inversion after cell divisions in Eudorina.[4]

Schematic representation of the phylogenetic relationships of the volvocine algae and the parallel evolution of the spheroidal colony. Volvocine algae range from the unicellular Chlamydomonas to the multicellular Volvox through various intermediate forms and are used as a model for research into the evolution of multicellularity. The spheroidal colony is thought to have evolved twice independently within this group: once in the Volvocaceae, from Pandorina to Volvox, and the other in the genus Astrephomene. The phylogeny is based on previous reports. All drawings and photographs represent side views of individuals with anterior ends orienting toward the top of this figure.[4]

Habitats

Astrephomene gubernaculifera is often found in organically rich temporary pools, often in pasture ponds. It typically persists for 1–3 weeks after ponds are formed in beginning of the wet season (Pocock 1953).

It has been collected from South Africa, Australia and the United States (Pocock 1953).

References

  1. ^ Nozaki, H.; Kuroiwa, T. (1992). "Ultrastructure of the extracellular matrix and taxonomy of Eudorina, Pleodorina and Yamagishiella gen. nov. (Volvocaceae, Chlorophyta)". Phycologia. 31 (6): 529–541. doi:10.2216/i0031-8884-31-6-529.1.
  2. ^ See the NCBI webpage on Astrephomene. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19.
  3. ^ Nozaki, H.; Kuroiwa, T. (1992). "Ultrastructure of the extracellular matrix and taxonomy of Eudorina, Pleodorina and Yamagishiella gen. nov. (Volvocaceae, Chlorophyta)". Phycologia. 31 (6): 529–541. doi:10.2216/i0031-8884-31-6-529.1.
  4. ^ a b c Yamashita S, Arakaki Y, Kawai-Toyooka H, Noga A, Hirono M, Nozaki H. Alternative evolution of a spheroidal colony in volvocine algae: developmentalanalysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta). BMC Evol Biol. 2016 Nov 9;16(1):243. PubMed PMID: 27829356; PubMed Central PMCID: PMC5103382. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.

Further reading

Scientific journals

  • Nozaki H, Onishi K, Morita E (2002). "Differences in pyrenoid morphology are correlated with differences in the rbcL genes of members of the Chloromonas lineage (Volvocales, Chlorophyceae)". J Mol Evol. 55 (4): 414–430. doi:10.1007/s00239-002-2338-9. PMID 12355262.
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