Volvox

//Volvox Carteri// ( F.Stein 1873)

"And God said, Let the waters bring forth abundantly the moving creatures that hath life, and fowl that may fly above the earth in the open firmament of heaven."

-Genesis 1, The Bible toc media type="custom" key="24399742" =**Description** =

=**Morphological notes **=

Mature Volvox colony is composed of numerous flagellated algal cells (Fig. 1), up to 50,000 in total. There are several types of cells in the colony. The asexual colony is mainly made up of somatic cells which are small and confer the ability to swim with distinct anterior and posterior poles. Eyespots of the anterior cells are more developed, hence allowing them to swim towards lights. Larger cells involved in asexual reproduction called gonidia are also present inside the colony, typically 8 to 16 of them (Nozaki and Coleman, 2011). Most often, one could observed daughter colonies developing inside the mother colony. In sexual colonies, sperm packs and female oogonia could be observed on male and female colonies respectively. Inhabitants within the colony are quite common. A small rotifer, called //Proales parasita// lives inside Volvox and feeds on the cells. The rotifer is able to detect when the colony becomes immobile. When Volvox is observed under the coverslip it may be trapped by the pressure of the cover-slip. Proales will quickly make a hole and escape.



=**Reproduction** =

//Volvox carteri // can reproduce both sexually and asexually. During asexual reproduction, individual gonidium divide through mitosis and develop into a daughter colony within the mother colony. The daughter colonies have flagella facing inward originally and eventually facing out through a process called inversion. Following which, the daughter colonies are freed from constrain of the mother colony upon colony breakage. Species within the genus //Volvox // can be both monoecious (bearing both sperm and egg on the same gametophyte) and diecious (bearing either sperm or egg but never both). During sexual production, the sperm packets dissociates from the male colonies and actively find female colonies. The sperms penetrates the extracellular matrix of female colonies and fertilize the eggs located in the oogonia. After fertilization, a zygote with a hard protective layer is formed which helps to withstand harsh conditions and survive through the winter.

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= = =**Habitats **=

//Volvox // are freshwater algae and are usually found in freshwater swamp, marsh, ponds forest stream, ditches and even shallow puddles. In Singapore, they could be found in Changi, Pulau Ubin, East Coast Park, Botanic Gardens etc (Wee, 1987).

=**Taxonomy and Phylogeny **=

The genus Volvox is polyphyletic (Larson et al. 1992). Based on molecular phylogenetic analysis, different species of Volvox closely related to different organisms with in the Volvocaceae family, indicating that the evolution of this multicellular spherical colonial algae has occurred multiple times. **Scientific Value** Volvox is a model organism in developmental biology (for review see Desnitskiĭ, 2009). Organisms within the Volvocalean order are highly related organisms with difference in mating behavior and cellular complexity.


 * Kingdom: || __ [|Plantae] __ ||
 * Phylum: || __ [|Chlorophyta] __ ||
 * Class: || __ [|Chlorophyceae] __ ||
 * Order: || __ [|Volvocales] __ ||
 * Family: || __ [|Volvocaceae] __ ||
 * Genus: || __ [|Volvox] __ ||
 * Species Example ||
 * __ [|Volvox] ____ [|carteri] ____ [|Volvox] ____ [|globator] ____ [|Volvox] ____ [|barberi] ____ [|Volvox] ____ [|rouseletti] __ ||



=<span style="font-family: Georgia,serif; line-height: 1.5;">Scientific Value =

//<span style="font-family: Georgia,serif;">**The study of** **Multicellularity** //
<span style="font-family: Georgia,serif;">Ancestors of Volvox transitioned from single cells to form multicellular colonies at least 200 million years ago, during the Triassic period (Herron et al., 2009). 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 (Herron et al., 2009).



<span style="font-family: Georgia,serif;">Sexual reproduction in Volvocine algae coevolved with the acquisition of multicellularity. Unicellular genera such as Chlamydomonas and small colonial genera from this group have classical mating types with equal-sized gametes, while larger multicellular genera such as Volvox have differentiated males and females that produce sperm and eggs respectively. Newly available sequence from the Volvox and Chlamydomonas genomes and mating loci revealed the gradual evolution of mating locus (MT) from simple unicellular organism to large complex multicellular volvox. (Umen, 2011)

=**<span style="font-family: Georgia,serif;">References **=

<span style="font-family: Georgia,serif;">Desnitskii, A. G. (2009). [Volvox (Chlorophyta, Volvocales) as a model organism in developmental biology]. Ontogenez, 40(4), 301-304.

<span style="font-family: Georgia,serif;">Larson, A., Kirk, M. M., & Kirk, D. L. (1992). Molecular phylogeny of the volvocine flagellates. Mol Biol Evol, 9(1), 85-105.

<span style="font-family: Georgia,serif;">Nishii, I., & Miller, S. M. (2010). Volvox: Simple steps to developmental complexity? Current Opinion in Plant Biology, 13(6), 646-653. doi: http://dx.doi.org/10.1016/j.pbi.2010.10.005

<span style="font-family: Georgia,serif;">Nishii, I., & Miller, S. M. (2010). Volvox: Simple steps to developmental complexity? Current Opinion in Plant Biology, 13(6), 646-653. doi: http://dx.doi.org/10.1016/j.pbi.2010.10.005

<span style="font-family: Georgia,serif;">Schmitt, R. (2003). Differentiation of germinal and somatic cells in Volvox carteri. Curr Opin Microbiol, 6(6), 608-613.