Volvox

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Volvox

• THE FIERCE ROLLER

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Why do they interest us?

• Individual cells that cooperate together in a
  colony to behave like a multicellular organism
• Good for studying the origins of multicellularity
  because easy to find (pond scum!), division of
  labor, well-studied, relatively young (can study
  genomes relatively untouched by genetic drift),
  easily manipulated

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How are they like multicellular organisms?

• Individual cells are connected to each other
  through cytoplasmic bridges formed from
  incomplete cytokinesis
• Each cell uses its flagella in unison with the
  other cells to propel the entire colony
• All cells dont have the same job division of
  labor (germ-soma)!
• Can undergo both asexual and sexual reproduction

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How does it move?

• Each cell has two flagella, but theyre not the
  same one is older than the other, and they move
  like in breast stroke
• Ca2 concentrations control which flagella
  dominates, allows the colony to turn, important
  for finding light or avoiding too much light
• Flagella stick out of the colony and propel

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How does it reproduce?

• Asexually not binary fission, but multiple
  fission. Grows to 2n times its own size and
  divides n times. Have bigger cells from
  asymmetric division, gonidia, do the dividing
  division of labor
• Sexually males secrete pheromone that cause
  other males to reproduce sexually. Used when
  conditions unfavorable to produce spores capable
  of withstanding harsh conditions sperm (divides)
  and egg (grows)
• Look!

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What can they tell us?

• Many different species of Volvox all evolved
  separately, relatively recently, can study to
  figure out how multicellularity arises (see
  handout for controversy) and the different routes
  the Volvox took (same genes for reproductive
  repression? Same molecular pathways to same
  morphological end? Modified old genes or new
  genes?)

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Sources

• http//micro.magnet.fsu.edu/moviegallery/pondscum/
  protozoa/volvox/index.html
• http//www.btinternet.com/stephen.durr/volvox.htm
  l
• http//protist.i.hosei.ac.jp/PDB/Images/Chlorophyt
  a/Volvox/
• http//www.microscopy-uk.org.uk/mag/indexmag.html?
  http//www.microscopy-uk.org.uk/mag/artdec03/volvo
  x.html
• Kirk, David L. Volvox Molecular-Genetic Origins
  of Multicellularity and Cellular Differentiation

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