''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 conver ...
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
of
chlorophyte
Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...
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 alg ...
in the family
Volvocaceae. 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 in ...
habitats, and were first reported by
Antonie van Leeuwenhoek in 1700. ''Volvox'' diverged from unicellular ancestors approximately .
Description
''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 conver ...
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 the ...
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
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 struc ...
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 g ...
s.
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
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. ...
, 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 multicell ...
s 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
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 th ...
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 ...
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 i ...
or
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 reproducti ...
.
Male
Male (Mars symbol, 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 sexual reproduction, repro ...
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 cells by a short
heat shock 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 detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal re ...
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 cellular ...
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''.
[ Material was copied from this source, which is available under ]
Creative Commons Attribution 4.0 International License
Habitats
''Volvox'' is a genus of freshwater algae found in ponds and ditches, even in shallow puddles.
According to
Charles Joseph Chamberlain
Charles Joseph Chamberlain, Ph.D. (February 23, 1863 – February 5, 1943) was an American botanist, born near Sullivan, Ohio, and educated at Oberlin College and at the University of Chicago, where he earned the first Ph.D. in that institution ...
,
"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' ...
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 "duckweed". They are morphologically divergent members of the arum family Araceae. These rapidly growing plants have found uses as a model system for studies in ...
'', 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'', ''Alisma
''Alisma'' is a genus of flowering plants in the family Alismataceae, members of which are commonly known as water-plantains. The genus consists of aquatic plants with leaves either floating or submerged, found in a variety of still water hab ...
'', '' Equisetum fluviatile'', ''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
British English (BrE, en-GB, or BE) is, according to Lexico, Oxford ...
'', 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
''Euglena'' is a genus of 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 ''Euglena'' are found in f ...
'', is often associated with these forms."
History
Antonie van Leeuwenhoek 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, t ...
(1758) would describe the genus ''Volvox'', with two species: ''
V. globator'' and ''V. chaos''. ''Volvox chaos'' is an amoeba now known as ''
Chaos (genus)'' 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.
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.
References
External links
*
''Volvox'' description with picturesfrom 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 l ...
website
*
YouTube
YouTube is a global online video sharing and 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 Google, and is the second most ...
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