''Volvox'' is a

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of converg ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of chlorophyte

green algae The green algae (singular: green alga) 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 ...

in the family

Volvocaceae The Volvocaceae are a family of unicellular or colonial biflagellates, including the typical genus ''Volvox''. The family was named by Ehrenberg in 1834,From p. 281: ''"VOLVOCINA Nova Familia."'' (Volvocina New Family.) ote: According to p. ...

. It forms spherical

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

of up to 50,000 cells. They live in a variety of

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

habitats, and were first reported by

Antonie van Leeuwenhoek Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch microbiologist and microscopist in the Golden Age of Dutch science and technology. A largely self-taught man in science, he is commonly known as " the ...

in 1700. ''Volvox'' diverged from unicellular ancestors approximately .

Description

''Volvox'' is a

genus in the volvocine green algae clade. Each mature ''Volvox''

colony In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the ''metropole, metropolit ...

is composed of up to thousands of cells from two differentiated cell types: numerous

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

somatic cells A somatic cell (from Ancient Greek σῶμα ''sôma'', meaning "body"), 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. Such cells compo ...

and a smaller number of

germ cell Germ or germs may refer to: Science * Germ (microorganism), an informal word for a pathogen * Germ cell, cell that gives rise to the gametes of an organism that reproduces sexually * Germ layer, a primary layer of cells that forms during embry ...

s lacking in soma that are embedded in the surface of a hollow sphere or coenobium containing an

extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...

made of

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

s. Adult

somatic Somatic may refer to: * Somatic (biology), referring to the cells of the body in contrast to the germ line cells ** Somatic cell, a non-gametic cell in a multicellular organism * Somatic nervous system, the portion of the vertebrate nervous sys ...

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 In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

, called protoplasmates. Cell number is specified during development and is dependent on the number of rounds of division.

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 and by the production of a sex-inducing pheromone. Desiccation-resistant diploid

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

s are produced following successful fertilization. An asexual colony includes both somatic (vegetative) cells, which do not reproduce, and large, non-motile ''

gonidia A gonidium (plural gonidia) is an asexual reproductive cell or group of cells, especially in alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping t ...

'' in the interior, which produce new colonies asexually through repeated division. In

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

two types of

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s are produced. ''Volvox'' species can be

monoecious Monoecy (; adj. monoecious ) is a sexual system in seed plants where separate male and female cones or flowers are present on the same plant. It is a monomorphic sexual system alongside gynomonoecy, andromonoecy and trimonoecy. Monoecy is conne ...

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

Male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot reproduce sexually without access to ...

colonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs. Kirk and Kirk showed that sex-inducing pheromone production can be triggered in

somatic cell A somatic cell (from Ancient Greek σῶμα ''sôma'', meaning "body"), 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. Such cells compo ...

s by a short

heat shock The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal ...

given to asexually growing organisms. The induction of sex by heat shock is mediated by

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily Detoxification, detoxify the reactive intermediates or to repair the resulting damage. Disturbances ...

that likely also causes oxidative DNA damage. It has been suggested that switching to the sexual pathway is the key to surviving environmental stresses that include heat and

drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...

. Consistent with this idea, the induction of sex involves a

signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...

pathway that is also induced in ''Volvox'' by wounding.

Colony inversion

Colony inversion is a special characteristic during development in the order Volvocaceae that results in new colonies having their

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

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 ''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 ''Chlamydomo ...

''.

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Inversion Process for Volvox

Habitats

''Volvox'' is a genus of freshwater algae found in ponds and ditches, even in shallow puddles. According to Charles Joseph Chamberlain,

"The most favorable place to look for it is in the deeper ponds,
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...
s, and ditches which receive an abundance of rain water. It has been said that where you find ''
Lemna ''Lemna'' is a genus of free-floating aquatic plants referred to by the common name "Lemnoideae, duckweed". They are morphologically divergent members of the arum family Araceae. These rapidly growing plants have found uses as a Model organism, m ...
'', 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 ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, peat moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store wa ...
'', ''
Vaucheria ''Vaucheria'' is a genus of Xanthophyceae or yellow-green algae known as water felt. It is one of only two genera in the family Vaucheriaceae. The type species of the genus is '' Vaucheria disperma''. The genus was circumscribed by Augustin Py ...
'', '' Alisma'', ''
Equisetum fluviatile ''Equisetum fluviatile'', the water horsetail or swamp horsetail, is a vascular plant that commonly grows in dense colonies along freshwater shorelines or in shallow water in ponds, swamps, ditches, and other sluggish or still waters with mud bo ...
'', ''
Utricularia ''Utricularia'', commonly and collectively called the bladderworts, is a genus of carnivorous plants consisting of approximately 233 species (precise counts differ based on classification opinions; a 2001 publication lists 215 species).Salmon, Br ...
'', ''
Typha ''Typha'' is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrush or reedmace, in American English as reed, cattail, or punks, in A ...
'', and '' Chara''. Dr. Nieuwland reports that ''
Pandorina ''Pandorina'' is a genus of green algae composed of 8, 16, or sometimes 32 Cell (biology), 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 Ke ...
'', ''
Eudorina ''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 indiv ...
'' and ''
Gonium ''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 ...
'' are commonly found as constituents of the green scum on wallows in fields where pigs are kept. The flagellate, ''
Euglena ''Euglena'' is a genus of Unicellular organism, single cell flagellate eukaryotes. It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species. Species of ''Eug ...
'', is often associated with these forms."

History

first reported observations of ''Volvox'' in 1700. After some drawings of Henry Baker (1753),

Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

(1758) would describe the genus ''Volvox'', with two species: '' V. globator'' and ''V. chaos''. ''Volvox chaos'' is an amoeba now known as ''

Chaos (genus) ''Chaos'' is a genus of single-celled amoeboid organisms in the family Amoebidae. The largest and best-known species, the so-called "giant amoeba" ''Chaos carolinensis'', can reach lengths of 5 mm, although most specimens fall between 1 an ...

'' sp.Spencer, M.A., Irvine, L.M. & Jarvis, C.E. (2009). Typification of Linnaean names relevant to algal nomenclature. ''Taxon'' 58: 237-260

.

Evolution

Ancestors of ''Volvox'' transitioned from single cells to form multicellular colonies at least , during the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. An estimate using

DNA sequence DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. Th ...

s 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.

References

External links

*
''Volvox'' description with pictures
from a

Hosei University is a private university based in Tokyo, Japan. The university originated in a school of law, Tōkyō Hōgakusha (, i.e. Tokyo association of law), established in 1880, and the following year renamed Tōkyō Hōgakkō (, i.e. Tokyo school of law ...

website *

YouTube YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...

videos of ''Volvox'': *
Volvox micro-motility in Lake Oroville, CA
*
Life cycle and inversion
*
Waltzing ''Volvox''
*
Spinning ''Volvox''

by Wim van Egmond, from Microscopy-UK
''Volvox carteri''
at MetaMicrobe.com, with modes of reproduction, brief facts {{Taxonbar, from=Q310495 1700 in science Chlamydomonadales Chlamydomonadales genera