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The More the Merrier?

The More the Merrier?. The Evolution of Multicellular Organisms. The Problem of Size. All animals need to exchange substances with the environment SURFACE AREA : VOLUME Bacteria – 6 000 000/m Whale – 0.06/m Maximum cell size is limited All organisms larger than size limit are MULTICELLULAR.

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The More the Merrier?

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  1. The More the Merrier? The Evolution of Multicellular Organisms

  2. The Problem of Size • All animals need to exchange substances with the environment • SURFACE AREA : VOLUME • Bacteria – 6 000 000/m • Whale – 0.06/m • Maximum cell size is limited • All organisms larger than size limit are MULTICELLULAR

  3. Solving the SA:V problem Geometric solutions • Increase surface area • Decrease effective volume Increase rate of supply • High concentration of nutrients • Improve nutrient transport within Improve efficiency to reduce demand • Division of labor within the cell • Division of labor between cells

  4. Evolution of multicellularity • Evolved many times in eukaryotes • Three theories • Symbiotic Theory • Like the endosymbiotic theory • Different species are involved • Syncytial Theory • Ciliates and slime molds • Commonly occur in multinucleated cells • Colonial Theory (Haeckel, 1874) • Same species are involved • Green algae (Chlorophyta) > 7000 species • Volvox

  5. Biofilms Unicellular prokaryotes Coordinate activity for own benefit Different species, same requirements Colony attaches to a surface Chemical communication to others Slime layer develops (Protein and polysaccharide) Diffusion between cells and fluid increases Cells regular pH and [food and wastes’ as a whole

  6. Where Are Biofilms?

  7. Chlamydomonas…or Volvox? • Unicellular flagellate • Individuals connected by strands of cytoplasm • Some individuals take on special roles. • Movement • Reproduction • If one cell dies, the rest survive • Volvox in Motion

  8. Gonium • Small colony (4, 8,16, or 32 cells) • No differentiation • Intercellular communication

  9. Pandorina • Colony (8, 16, or 32 cells) in 1 layer • Spherical • Anterior cells  larger eyespots • Coordinate flagellar movement • Colony dies when disrupted

  10. Eudorina • 16 or 32 cells • 16 cells – no specialization • 32 – 4 for motility, the rest for reproduction • Heterogamy – female gametes not released • Halves are more pronounced

  11. Pleodorina • 32 to 128 cells • Heterogamy – female gametes not released, in some cases becoming truly non-motile • Division of labor • Anterior vegetative cells • Larger posterior reproductive cells

  12. Volvox • Spherical colonies (500-50000 cells) • Hollow sphere – coenobium • Cell differentiation: somatic/vegetative cells and gonidia • 2-50 scattered in the posterior  reproductive • Female reproductive cells  daughter colonies • Intercellular communication possible

  13. Anisogamy Anisogamy/ Heterogamy

  14. Social Amoeba:Dictyosteliumdiscoideum We are the scientists in the lab Looking through a microscope Those little glass slides they never lie How can this small mind cope? I've never seen anything like it before This amoeba's got a mind of its own "Amoeba" by The Adolescents

  15. Amoeba Slugs Forming (About 2mm)

  16. Life Cycle

  17. All Cells In A Multicellular Organism Must, At Some Point… Adhere Communicate Move Differentiate In that order? By what mechanism?

  18. In case you need more videos http://www.youtube.com/watch?v=OX5Yiz38fgY&feature=related http://www.youtube.com/watch?v=Ql7i_TLUurM&feature=relatedhttp://www.youtube.com/watch?v=YoXWbr45rsQ http://www.youtube.com/watch?v=4VwFMqZ5KeY http://www.youtube.com/watch?v=R_nPFJlH1Vk http://www.youtube.com/watch?v=YoXWbr45rsQ “Homo Amoeba” is a artistic and entertaining look at cell movement: http://www.youtube.com/watch?v=7jd0QEe_WHE The BioClip “Day in the Life of Social Amoeba” deserves special mention for excellent design; you may have to contact Kota Miura (via www.bioclips.com) who was kind enough to email me a link to download the clip: http://www.bioclips.com/research.php3?id_article=56

  19. What Can We Learn From Social Amoeba? Chemotaxis: how cells move Cell-cell communication (chemical) Cell connection (membrane proteins) Behavior: Competition, altruism…and cheating Immune systems (sentinel cells) Molecular genetics & Development Evo-Devo Evolution, evolution, evolution!

  20. Advantages of multicellularity • Increase in size of the organism • Permits cell specialization • Increase in surface area to volume ratio

  21. Problems of multicellularity • Interdependence • Complexity

  22. Images • http://protist.i.hosei.ac.jp/pdb/images/Chlorophyta/Gonium/pectorale/sp_2b.jpg • http://www.rbgsyd.nsw.gov.au/__data/assets/image/48212/Gonium2.gif • http://www.ac-rennes.fr/pedagogie/svt/photo/microalg/pandorin.jpg • http://protist.i.hosei.ac.jp/PDB/images/Chlorophyta/Eudorina/elegans/sp_5.jpg • http://www.fytoplankton.cz/FytoAtlas/thm/0078.jpg

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