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Volvox

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Volvox
Volvoxsp.
Scientific classificationEdit this classification
(unranked): Viridiplantae
Division: Chlorophyta
Class: Chlorophyceae
Order: Chlamydomonadales
Family: Volvocaceae
Genus: Volvox
L.
Species

Volvox aureus
Volvox carteri(V. nagariensis)
Volvox globator
Volvox barberi
Volvox rouseletti
Volvox dissipatrix
Volvox tertius

Volvoxis apolyphyleticgenusofchlorophytegreen algaein the familyVolvocaceae.Volvoxspecies form sphericalcoloniesof up to 50,000 cells, and for this reason they are sometimes calledglobe algae.They live in a variety offreshwaterhabitats, and were first reported byAntonie van Leeuwenhoekin 1700.Volvoxdiverged from unicellular ancestors approximately200million years ago.[1]

Description

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Volvoxcolony: 1)Chlamydomonas-like cell, 2) Daughter colony, 3) Cytoplasmic bridges, 4) Intercellular gel, 5) Reproductive cell, 6) Somatic cell.

Volvoxis apolyphyleticgenus in the volvocine green algae clade.[2]Each matureVolvoxcolonyis composed of up to thousands of cells from two differentiated cell types: numerousflagellatesomatic cellsand a smaller number ofgerm cellslacking in soma that are embedded in the surface of a hollow sphere orcoenobiumcontaining anextracellular matrix[1]made ofglycoproteins.[3]

Adultsomaticcells comprise a single layer with the flagella facing outward. The cells swim in a coordinated fashion, with distinct anterior and posterior poles. The cells have anterioreyespotsthat enable the colony to swim toward light. The cells of colonies in the more basalEuvolvoxclade are interconnected by thin strands ofcytoplasm,called protoplasmates.[4]Cell number is specified during development and is dependent on the number of rounds of division.[2]

Reproduction

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Volvoxis facultatively sexual and can reproduce both sexually and asexually. In the lab, asexual reproduction is most commonly observed; the relative frequencies of sexual and asexual reproduction in the wild is unknown. The switch from asexual to sexual reproduction can be triggered by environmental conditions[5]and by the production of a sex-inducing pheromone.[6]Desiccation-resistant diploidzygotesare produced following successful fertilization.

Anasexualcolony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motilegonidiain the interior, which produce new colonies asexually through repeated division. Insexual reproductiontwo types ofgametesare produced.Volvoxspecies can bemonoeciousordioecious.Malecolonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs.[2][7]

Kirk and Kirk[8]showed that sex-inducing pheromone production can be triggered insomatic cellsby a shortheat shockgiven to asexually growing organisms. The induction of sex by heat shock is mediated byoxidative stressthat likely also causes oxidative DNA damage.[5][9]It has been suggested that switching to the sexual pathway is the key to surviving environmental stresses that include heat anddrought.[10]Consistent with this idea, the induction of sex involves asignal transductionpathway that is also induced inVolvoxby wounding.[10]

Colony inversion

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Colony inversion is a special characteristic during development in the order Volvocaceae that results in new colonies having theirflagellafacing outwards. During this process the asexual reproductive cells (gonidia) first undergo successive cell divisions to form a concave-to-cup-shaped embryo or plakea composed of a single cell layer. Immediately after, the cell layer is inside out compared with the adult configuration—the apical ends of the embryo protoplasts from which flagella are formed, are oriented toward the interior of the plakea. Then the embryo undergoes inversion, during which the cell layer inverts to form a spheroidal daughter colony with the apical ends and flagella of daughter protoplasts positioned outside. This process enables appropriate locomotion of spheroidal colonies of the Volvocaceae. The mechanism of inversion has been investigated extensively at the cellular and molecular levels using the model species,Volvox carteri.[11]

Embryonic inversion in Volvox. (a) Adult V. globator spheroid containing multiple embryos. (b) Embryo undergoing type-A inversion (e.g., V. carteri). (c) Embryo undergoing type-B inversion (e.g., V. globator, V. aureus). (d) Light micrograph shows semi-thin section of V. globator embryo exhibiting different cell shapes. (e) Schematic representation of cells in region marked in (d). PC: paddle-shaped cells, two different views illustrate anisotropic shape; SC: spindle-shaped cells; red line: position of cytoplasmic bridges (CB). (f) 3D renderings of a single V. globator embryo in three successive stages of inversion. (g) Optical midsagittal cross sections of embryo in (f). (h) Traced cell sheet contours overlaid on sections in (g), with color-coded curvature κ. (i) Surfaces of revolution computed from averaged contours.[12]

Habitats

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Volvoxis a genus of freshwater algae found in ponds and ditches, even in shallow puddles.[7]According toCharles Joseph Chamberlain,[13]

"The most favorable place to look for it is in the deeper ponds,lagoons,and ditches which receive an abundance of rain water. It has been said that where you findLemna,you are likely to findVolvox;and it is true that such water is favorable, but the shading is unfavorable. Look where you findSphagnum,Vaucheria,Alisma,Equisetum fluviatile,Utricularia,Typha,andChara.Dr. Nieuwland reports thatPandorina,EudorinaandGoniumare commonly found as constituents of the green scum on wallows in fields where pigs are kept. The flagellate,Euglena,is often associated with these forms. "

History

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Antonie van Leeuwenhoekfirst reported observations ofVolvoxin 1700.[14][15]

After some drawings ofHenry Baker(1753),[16]Linnaeus(1758)[17]would describe the genusVolvox,with two species:V. globatorandV. chaos.Volvox chaosis an amoeba now known asChaossp.[18][19]

Evolution

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Ancestors ofVolvoxtransitioned from single cells that initially resembledChlamydomonasto form multicellular colonies at least200million years ago,during theTriassicperiod.[1][20] The middle stage, Conium, contained 16 chlamydomonas-like cells. An estimate usingDNA sequencesfrom about 45 different species of volvocine green algae, includingVolvox,suggests that the transition from single cells to undifferentiated multicellular colonies took about 35 million years.[1][20]

References

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  1. ^abcdUniversity of Arizona (February 22, 2009)."Single-celled algae took the leap to multicellularity 200 million years ago".Science Daily.
  2. ^abcKirk, David L. (1998).Volvox:A Search for the Molecular and Genetic Origins of Multicellularity and Cellular Differentiation.Cambridge University Press.ISBN978-0-521-45207-6.
  3. ^Hallmann, A. (2003). "Extracellular Matrix and Sex-Inducing Pheromone in Volvox".Extracellular matrix and sex-inducing pheromone inVolvox.International Review of Cytology. Vol. 227. pp. 131–182.doi:10.1016/S0074-7696(03)01009-X.ISBN978-0-12-364631-6.PMID14518551.
  4. ^Ikushima, N.; Maruyama, S. (1968). "The protoplasmic connection inVolvox".Journal of Eukaryotic Microbiology.15(1): 136–140.doi:10.1111/j.1550-7408.1968.tb02098.x.
  5. ^abNedelcu, AM; Michod, RE (2003)."Sex as a response to oxidative stress: the effect of antioxidants on sexual induction in a facultatively sexual lineage".Proc. Biol. Sci.270(Suppl 2): S136–9.doi:10.1098/rsbl.2003.0062.PMC1809951.PMID14667362.
  6. ^Hallmann, Armin (2003). "Extracellular Matrix and Sex-Inducing Pheromone in Volvox".International Review of Cytology.227:131–182.doi:10.1016/S0074-7696(03)01009-X.ISBN978-0-12-364631-6.PMID14518551.
  7. ^abPowers, J. H. (1908). "Further studies inVolvox,with descriptions of three new species ".Transactions of the American Microscopical Society.28:141–175.doi:10.2307/3220908.JSTOR3220908.
  8. ^DL, Kirk; Kirk, MM (1986). "Heat shock elicits production of sexual inducer in Volvox".Science.231(4733): 51–4.Bibcode:1986Sci...231...51K.doi:10.1126/science.3941891.PMID3941891.
  9. ^Nedelcu, AM; Marcu, O; Michod, RE (2004)."Sex as a response to oxidative stress: a twofold increase in cellular reactive oxygen species activates sex genes".Proc. Biol. Sci.271(1548): 1591–6.doi:10.1098/rspb.2004.2747.PMC1691771.PMID15306305.
  10. ^abAmon, P; Haas, E; Sumper, M (1998)."The sex-inducing pheromone and wounding trigger the same set of genes in the multicellular green alga Volvox".Plant Cell.10(5): 781–9.doi:10.2307/3870664.JSTOR3870664.PMC144025.PMID9596636.
  11. ^Yamashita, S; Arakaki, Y; Kawai-Toyooka, H; Noga, A; Hirono, M; Nozaki, H (Nov 2016)."Alternative evolution of a spheroidal colony in volvocine algae: developmentalanalysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta)".BMC Evol. Biol.16(1): 243.doi:10.1186/s12862-016-0794-x.PMC5103382.PMID27829356.Material was copied from this source, which is available under aCreative Commons Attribution 4.0 International License.
  12. ^Stephanie Höhn, Aurelia R. Honerkamp-Smith, Pierre A. Haas, Philipp Khuc Trong, and Raymond E. Goldstein Phys. Rev. Lett. 114, 178101 – Published 27 April 2015.This article contains quotations from this source, which is available under theCreative Commons Attribution 3.0 (CC BY 3.0)license.
  13. ^Chamberlain, Charles Joseph(2007) [1932]."Chlorophyceae".Methods in Plant Histology.Read Books. pp. 162–180.ISBN978-1-4086-2795-2.
  14. ^van Leeuwenhoek, Antonie(1700)."Part of a Letter from Mr Antony van Leeuwenhoek, concerning the Worms in Sheeps Livers, Gnats, and Animalcula in the Excrements of Frogs".Philosophical Transactions of the Royal Society.22(260–276): 509–518.Bibcode:1700RSPT...22..509V.doi:10.1098/rstl.1700.0013.
  15. ^Herron, M. (2015). "…of the bignefs of a great corn of fand…".Fierce Roller Blog,[1]Archived2016-06-03 at theWayback Machine.
  16. ^Baker, H. (1753).Employment for the microscope.R. Dodsley: London, pl. XII, f. 27,[2].
  17. ^Linnaeus, C. (1758).Systema naturaeper regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis.Tomus I. Editio decima, reformata. Editio decima revisa. Vol. 1 pp. [i-iv], [1]-823. Holmiae [Stockholm]: impensis direct. Laurentii Salvii.
  18. ^Herron, M. (2016). Moving without limbs! Linnaeus on Volvox.Fierce Roller Blog,[3]Archived2016-06-03 at theWayback Machine.
  19. ^Spencer, M.A., Irvine, L.M. & Jarvis, C.E. (2009). Typification of Linnaean names relevant to algal nomenclature.Taxon58: 237-260,[4]Archived2016-05-08 at theWayback Machine.
  20. ^abHerron, MD; Hackett, JD; Aylward, FO; Michod, RE (2009)."Triassic origin and early radiation of multicellular volvocine algae".Proceedings of the National Academy of Sciences, USA.106(9): 3254–3258.Bibcode:2009PNAS..106.3254H.doi:10.1073/pnas.0811205106.PMC2651347.PMID19223580.
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