Volvox

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Volvox
Mikrofoto.de-volvox-4.jpg
Volvox sp.
Scientific classification OOjs UI icon edit-ltr.svg
(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

Contents

Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. Volvox species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox diverged from unicellular ancestors approximately 200  million years ago. [1]

Description

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

Volvox is a polyphyletic genus in the volvocine green algae clade. [2] Each mature Volvox colony is composed of up to thousands of cells from two differentiated cell types: numerous flagellate somatic cells and a smaller number of germ cells lacking in soma that are embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix [1] made of glycoproteins. [3]

Adult somatic cells 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 anterior eyespots that enable the colony to swim toward light. The cells of colonies in the more basal Euvolvox clade are interconnected by thin strands of cytoplasm, called protoplasmates. [4] Cell number is specified during development and is dependent on the number of rounds of division. [2]

Reproduction

Volvox is 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 diploid zygotes are produced following successful fertilization.

An asexual colony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motile gonidia in the interior, which produce new colonies asexually through repeated division. In sexual reproduction two types of gametes are produced. Volvox species can be monoecious or dioecious. Male colonies 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 in somatic cells by a short heat shock given to asexually growing organisms. The induction of sex by heat shock is mediated by oxidative stress that 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 and drought. [10] Consistent with this idea, the induction of sex involves a signal transduction pathway that is also induced in Volvox by wounding. [10]

Colony inversion

Colony inversion is a special characteristic during development in the order Volvocaceae that results in new colonies having their flagella facing 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 k. (i) Surfaces of revolution computed from averaged contours. Inversion Process for Volvox.png
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.

Habitats

Volvox is a genus of freshwater algae found in ponds and ditches, even in shallow puddles. [7] According to Charles 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 find Lemna , you are likely to find Volvox; and it is true that such water is favorable, but the shading is unfavorable. Look where you find Sphagnum , Vaucheria , Alisma , Equisetum fluviatile , Utricularia , Typha , and Chara . Dr. Nieuwland reports that Pandorina , Eudorina and Gonium are 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

Antonie van Leeuwenhoek first reported observations of Volvox in 1700. [14] [15]

After some drawings of Henry Baker (1753), [16] Linnaeus (1758) [17] would describe the genus Volvox, with two species: V. globator and V. chaos. Volvox chaos is an amoeba now known as Chaos (genus) sp. [18] [19]

Evolution

Ancestors of Volvox transitioned from single cells that initially resembled Chlamydomonas to form multicellular colonies at least 200  million years ago, during the Triassic period. [1] [20] The middle stage, Conium, contained 16 chlamydomonas-like cells. An estimate using DNA sequences from about 45 different species of volvocine green algae, including Volvox, suggests that the transition from single cells to undifferentiated multicellular colonies took about 35 million years. [1] [20]

Related Research Articles

<span class="mw-page-title-main">Asexual reproduction</span> Reproduction without a sexual process

Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. Asexual reproduction is the primary form of reproduction for single-celled organisms such as archaea and bacteria. Many eukaryotic organisms including plants, animals, and fungi can also reproduce asexually. In vertebrates, the most common form of asexual reproduction is parthenogenesis, which is typically used as an alternative to sexual reproduction in times when reproductive opportunities are limited. Komodo dragons and some monitor lizards can reproduce asexually.

<span class="mw-page-title-main">Chlorophyceae</span> Class of green algae

The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral- or ribbon-shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.

<span class="mw-page-title-main">Volvocaceae</span> Family of algae

The Volvocaceae are a family of unicellular or colonial biflagellates, including the typical genus Volvox. The family was named by Ehrenberg in 1834, and is known in older classifications as the Volvocidae. All species are colonial and inhabit freshwater environments.

<span class="mw-page-title-main">Chlamydomonadales</span> Order of green algae

Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae. Chlamydomonadales can form planar or spherical colonies. These vary from Gonium up to Volvox. Each cell has two flagella, and is similar in appearance to Chlamydomonas, with the flagella throughout the colony moving in coordination.

In cellular biology, a somatic cell, or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. Somatic cells compose the body of an organism and divide through the process of binary fission and mitotic division.

<span class="mw-page-title-main">Multicellular organism</span> Organism that consists of more than one cell

A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium.

<span class="mw-page-title-main">Biological life cycle</span> Series of stages of an organism

In biology, a biological life cycle is a series of stages of the life of an organism, that begins as a zygote, often in an egg, and concludes as an adult that reproduces, producing an offspring in the form of a new zygote which then itself goes through the same series of stages, the process repeating in a cyclic fashion.

<span class="mw-page-title-main">Green algae</span> Paraphyletic group of autotrophic eukaryotes in the clade Archaeplastida

The green algae are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as sister of the Zygnematophyceae. Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.

<i>Pandorina</i> Genus of algae

Pandorina is a genus of green algae composed of 8, 16, or sometimes 32 cells, held together at their bases to form a sack globular colony surrounded by mucilage. The cells are ovoid or slightly narrowed at one end to appear keystone- or pear-shaped. Each cell has two flagella with two contractile vacuoles at their base, an eyespot, and a large cup-shaped chloroplast with at least one pyrenoid.

Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction. Sex pheromones specifically focus on indicating females for breeding, attracting the opposite sex, and conveying information on species, age, sex and genotype. Non-volatile pheromones, or cuticular contact pheromones, are more closely related to social insects as they are usually detected by direct contact with chemoreceptors on the antennae or feet of insects.

<i>Gonium</i> Genus of algae

Gonium is a genus of colonial algae, a member of the order Chlamydomonadales. Typical colonies have 4 to 16 cells, all the same size, arranged in a flat plate, with no anterior-posterior differentiation. In a colony of 16 cells, four are in the center, and the other 12 are on the four sides, three each. A description by G.M. Smith :

Gonium Mueller 1773: Colonies of 4-8-16 cells arranged in a flat quadrangular plate and embedded in a common gelatinous matrix or connected by broad gelatinous strands. Cells ovoid to pyriform, with a single cup-shaped chloroplast containing one pyrenoid. Each cell with two cilia of equal length, contractile vacuoles at the base of the cilia, and an eyespot. Four- and eight-celled colonies with the cilia on the same side ; sixteen-celled colonies with the four central cells having their cilia on the same side and the twelve marginal cells with radially arranged cilia.

Asexual reproduction by simultaneous division of all cells in the colony to form autocolonies, or by a formation of 2-4 zoospores in each cell.

Sexual reproduction isogamous, by a fusion of biciliatezoogametes.

Astrephomene is a genus of green algae in the family Goniaceae, order Chlamydomonadales. The genus was first described in 1937 by Pocock and named by Pockock in 1953.

<i>Eudorina</i> Genus of algae

Eudorina is a paraphyletic genus in the volvocine green algae clade. Eudorina colonies consist of 16, 32 or 64 individual cells grouped together. Each individual cell contains flagella which allow the colony to move as a whole when the individual cells beat their flagella together. Description by GM Smith :

<i>Platydorina</i> Genus of algae

Platydorina is a genus of microscopic green algae in the family Volvocaceae. It contains only one species, Platydorina caudata. It was described by Charles Atwood Kofoid in 1899.

<i>Stephanosphaera</i> Genus of algae

Stephanosphaera is a genus of green algae in the family Haematococcaceae, containing the single species Stephanosphaera pluvialis. It forms colonies of flagellated cells. Although it was once placed in the family Volvocaceae, it is not closely related to them; its sister is the unicellular genus Balticola.

<span class="mw-page-title-main">Sexual reproduction</span> Reproduction process that creates a new organism by combining the genetic material of two organisms

Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes combines with another gamete to produce a zygote that develops into an organism composed of cells with two sets of chromosomes (diploid). This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes.

<i>Volvox globator</i> Species of alga

Volvox globator is a species of green algae of the genus Volvox. It was originally described by Carl Linnaeus in his 1758 work Systema Naturae. In 1856 its sexuality was described by Ferdinand Cohn and is the same as Sphaeropleaannulina. It is colonial flagellate found in freshwaters. The colony consists of thousands of zooids arranged in a single peripheral layer. each zooids shows two flagella, two or more contractile vacuoles, cup like chloroplast, a single nucleus, a red stigma but no gullet. Nutrition is holophytic. Size of colony increases by binary fission. In the colony the zooids called parthenogonidia repeatedly divide to form daughter colonies which are released from parent colony.

<i>Volvox carteri</i> Species of alga

Volvox carteri is a species of colonial green algae in the order Volvocales. The V. carteri life cycle includes a sexual phase and an asexual phase. V. carteri forms small spherical colonies, or coenobia, of 2000–6000 Chlamydomonas-type somatic cells and 12–16 large, potentially immortal reproductive cells called gonidia. While vegetative, male and female colonies are indistinguishable; however, in the sexual phase, females produce 35-45 eggs and males produce up to 50 sperm packets with 64 or 128 sperm each.

The origin and function of meiosis are currently not well understood scientifically, and would provide fundamental insight into the evolution of sexual reproduction in eukaryotes. There is no current consensus among biologists on the questions of how sex in eukaryotes arose in evolution, what basic function sexual reproduction serves, and why it is maintained, given the basic two-fold cost of sex. It is clear that it evolved over 1.2 billion years ago, and that almost all species which are descendants of the original sexually reproducing species are still sexual reproducers, including plants, fungi, and animals.

Germ-Soma Differentiation is the process by which organisms develop distinct germline and somatic cells. The development of cell differentiation has been one of the critical aspects of the evolution of multicellularity and sexual reproduction in organisms. Multicellularity has evolved upwards of 25 times, and due to this there is great possibility that multiple factors have shaped the differentiation of cells. There are three general types of cells: germ cells, somatic cells, and stem cells. Germ cells lead to the production of gametes, while somatic cells perform all other functions within the body. Within the broad category of somatic cells, there is further specialization as cells become specified to certain tissues and functions. In addition, stem cell are undifferentiated cells which can develop into a specialized cell and are the earliest type of cell in a cell lineage. Due to the differentiation in function, somatic cells are found ony in multicellular organisms, as in unicellular ones the purposes of somatic and germ cells are consolidated in one cell.

References

  1. 1 2 3 4 University of Arizona (February 22, 2009). "Single-celled algae took the leap to multicellularity 200 million years ago". Science Daily .
  2. 1 2 3 Kirk, David L. (1998). Volvox: A Search for the Molecular and Genetic Origins of Multicellularity and Cellular Differentiation. Cambridge University Press. ISBN   978-0-521-45207-6.
  3. ↑ Hallmann, A. (2003). "Extracellular Matrix and Sex-Inducing Pheromone in Volvox". Extracellular matrix and sex-inducing pheromone in Volvox. International Review of Cytology. Vol. 227. pp. 131–182. doi:10.1016/S0074-7696(03)01009-X. ISBN   978-0-12-364631-6. PMID   14518551.
  4. ↑ Ikushima, N.; Maruyama, S. (1968). "The protoplasmic connection in Volvox". Journal of Eukaryotic Microbiology . 15 (1): 136–140. doi:10.1111/j.1550-7408.1968.tb02098.x.
  5. 1 2 Nedelcu, 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. PMC   1809951 . PMID   14667362.
  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. ISBN   978-0-12-364631-6. PMID   14518551.
  7. 1 2 Powers, J. H. (1908). "Further studies in Volvox, with descriptions of three new species". Transactions of the American Microscopical Society . 28: 141–175. doi:10.2307/3220908. JSTOR   3220908.
  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. PMID   3941891.
  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. PMC   1691771 . PMID   15306305.
  10. 1 2 Amon, 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. JSTOR   3870664. PMC   144025 . PMID   9596636.
  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 . PMC   5103382 . PMID   27829356. CC-BY icon.svg Material was copied from this source, which is available under a Creative 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. CC-BY icon.svg This article contains quotations from this source, which is available under the Creative 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. ISBN   978-1-4086-2795-2.
  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, Archived 2016-06-03 at the Wayback Machine .
  16. ↑ Baker, H. (1753). Employment for the microscope. R. Dodsley: London, pl. XII, f. 27, .
  17. ↑ Linnaeus, C. (1758). Systema naturae per 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, Archived 2016-06-03 at the Wayback Machine .
  19. ↑ Spencer, M.A., Irvine, L.M. & Jarvis, C.E. (2009). Typification of Linnaean names relevant to algal nomenclature. Taxon 58: 237-260, Archived 2016-05-08 at the Wayback Machine .
  20. 1 2 Herron, 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 . PMC   2651347 . PMID   19223580.
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