View source for Volvox

=== 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]]''.<ref name="Yamashita">{{cite journal |last1=Yamashita |first1=S |last2=Arakaki |first2=Y |last3=Kawai-Toyooka |first3=H |last4=Noga |first4=A |last5=Hirono |first5=M |last6=Nozaki |first6=H |date=Nov 2016 |title=Alternative evolution of a spheroidal colony in volvocine algae: developmentalanalysis of embryogenesis in Astrephomene (Volvocales, Chlorophyta) |journal=BMC Evol. Biol. |volume=16 |issue=1 |page=243 |pmid=27829356 |doi=10.1186/s12862-016-0794-x |pmc=5103382 |bibcode=2016BMCEE..16..243Y |doi-access=free }} [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref> Another species ''[[Volvox globator]]'' has a similar mode of colony inversion, but begins at the posterior instead of the anterior.<ref name=Herron/>

[[File:Inversion Process for Volvox.png|899x899px|thumb|center|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.<ref>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. [[File:CC-BY icon.svg|50px]] This article contains quotations from this source, which is available under the [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 (CC BY 3.0)] license.</ref>]]