Volvox is a genus of chlorophytes, a type of green algae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox developed its colonial lifestyle .
Volvox is the most developed in a series of genera that form spherical colonies. Each mature Volvox colony is composed of numerous flagellate cells similar to Chlamydomonas, up to 50,000 in total, and embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of a gelatinous glycoprotein. The cells swim in a coordinated fashion, with distinct anterior and posterior poles. The cells have eyespots, more developed near the anterior, which enable the colony to swim towards light. The individual algae in some species are interconnected by thin strands of cytoplasm, called protoplasmates.
An asexual colony includes both somatic (vegetative) cells, which do not reproduce, and gonidia near the posterior, which produce new colonies through repeated division. The daughter colonies are initially held within the parent coenobium and have their flagella directed inwards. Later, the parent disintegrates and the daughters invert. In sexual reproduction two types of gametes are produced. Volvox species can be monoecious or dioecious. Male colonies release numerous microgametes, or sperm, while in female colonies single cells enlarge to become oogametes, or eggs.
"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 in summer as constituents of the green scum on wallows in fields where pigs are kept. The flagellate, Euglena, is often associated with these forms."
Ancestors of Volvox transitioned from single cells to form multicellular colonies at least Triassic period. An estimate using DNA sequences from about 45 different species of Volvox and related species suggests that the transition from single cells to undifferentiated multicellular colonies took about 35 million years., during the
- ^ a b David L. Kirk (1998). Volvox: A Search for the Molecular and Genetic Origins of Multicellularity and Cellular Differentiation. Cambridge University Press. ISBN 9780521452076.
- ^ a b c d "Single-celled algae took the leap to multicellularity 200 million years ago". Science Daily. February 22, 2009. http://www.sciencedaily.com/releases/2009/02/090219140546.htm.
- ^ A. Hallmann (2003). "Extracellular matrix and sex-inducing pheromone in Volvox". International Review of Cytology 227: 131–182. doi:10.1016/S0074-7696(03)01009-X.
- ^ N. Ikushima & S. Maruyama (1968). "The protoplasmic connection in Volvox". Journal of Eukaryotic Microbiology 15 (1): 136–140. doi:10.1111/j.1550-7408.1968.tb02098.x.
- ^ a b J. H. Powers (1908). "Further studies in Volvox, with descriptions of three new species". Transactions of the American Microscopical Society 28: 141–175. doi:10.2307/3220908. http://www.jstor.org/stable/3220908.
- ^ Charles Joseph Chamberlain (1932, reprinted 2007). "Chlorophyceae". Methods in Plant Histology. Read Books. pp. 162–180. ISBN 9781408627952. http://books.google.co.uk/books?id=O85ZudgVASEC&pg=PA165.
- ^ Antonie van Leeuwenhoek (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: 509. doi:10.1098/rstl.1700.0013. http://rstl.royalsocietypublishing.org/content/22/260-276/509.full.pdf+html.
- ^ a b 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: 3254–3258. doi:10.1073/pnas.0811205106.