The Origin Of Multicellularity And The Volvocine Series (PDF)

The Evolution of Multicellular Organisms MR. JULIUS A. GARCIA  Describe how Evaluate the multicellular forms advantages and may have evolved disadvantages of from protists, and multicellularity THE PROBLEM OF SIZE All animals need to exchange substances with the environmen...

The Evolution of Multicellular Organisms MR. JULIUS A. GARCIA  Describe how Evaluate the multicellular forms advantages and may have evolved disadvantages of from protists, and multicellularity THE PROBLEM OF SIZE All animals need to exchange substances with the environment  SURFACE AREA : VOLUME  Bacteria – 6 000 000/m Diffusion  Whale – 0.06/m Surface area  Maximum size limit of Difference in single cell concentration  All organisms larger than Distance size limit are MULTICELLULAR  Surface area to volume ratio gets smaller as the cell gets larger!  Avoidance  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  EVOLUTION OF MULTICELLULARITY  Evolved many times in eukaryotes  Three theories  Colonial Theory (Haeckel,  Symbiotic Theory 1874)  Like the endosymbiotic  Same species are involved theory  Green algae (Chlorophyta)  Different species are > 7000 species involved  Model: Volvocine series –  Syncytial Theory Order Volvocales  Ciliates and slime molds  Commonly occurs in multinucleated cells Unicellular Isogamy flagellate  GONIUM  Small colony (4, 8,16, or 32 cells)  Flat plane, mucilage  No differentiation  Isogamy  Intercellular communication PANDORINA  Colony (8, 16, or 32 cells) in 1 layer  Spherical  Isogamy  Anterior cells  larger eyespots  Coordinate flagellar movement  Colony dies when disrupted  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 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  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 Reproduction in the Volvox  Types of Reproduction Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Simplified diagram for stepwise evolution of colonial volvocine algae and their transition from isogamy to anisogamy and oogamy (Nozaki 2003; Herron et al. 2009).  Unicellular  colonial life  Increase in # of cells in colonies  Change in shape of colony  Increase in interdependence among vegetative cells  Increase in division of labor: vegetative and reproductive cells  Isogamy  anisogamy  oogamy  Fewer female gametes are produced  Increase in size of the organism  Permits cell specialization  Increase in surface area to volume ratio  Interdependence  Complexity  https://youtu.be/-ksYl2VvIHc  http://protist.i.hosei.ac.jp/pdb/ima ges/Chlorophyta/Gonium/pectoral e/sp_2b.jpg  http://www.rbgsyd.nsw.gov.au/__d ata/assets/image/48212/Gonium2. gif  http://www.ac- rennes.fr/pedagogie/svt/photo/mi croalg/pandorin.jpg  http://protist.i.hosei.ac.jp/PDB/ima ges/Chlorophyta/Eudorina/elegan s/sp_5.jpg  http://www.fytoplankton.cz/FytoAtl as/thm/0078.jpg