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Kingdom Protista Protista and the Origin of Metazoans Protista Defy Tidy Definition

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SEM of Paramecium Explain, in the context of evolution, why there is more higher order diversity (e.g. phyla) in the ocean but a greater species diversity on land. Kingdom Protista (Based on Textbook Chapter 3) Protista and the Origin of Metazoans Protista Defy Tidy Definition: Goals: Introduction - >10 phyla, believed by Review characteristics of single I. Body Plan some that they should be cell body plan classified as Kingdoms A. S.A./Volume Constraint Explore the limitations of life B. Reynolds number as a single cell - Among them are the II. Important Protists ancestors of multicell Learn some of the ways in which protists are important A. In food webs organisms including B. Agents of disease Evaluate evidence for the origin animals. of animals from protist ancestors III. Origin of Metazoans Evidence for colonial origin and metazoan ancestors Body plan characterized by: Most Common TYPES of Protista: Ciliates (Phylum Ciliophora): externally ciliated A. Unicellularity (most) B. Small Size (< 5-250 µm) Sarcodinids: 4 phyla of amoeboid types C. Lacking Organ Systems (Amoebas, foramenifera, radiozoans, heliozoans) (including a nervous system) Flagellates: several phyla of flagella-bearing types, including many photosynthetic forms and Each individual is a cell that is Some important parasitic forms functionally more versatile than any single cell from a multicell organism Spore-Formers: Phylum Apicomplexa and other very important parasitic forms 1 Means of locomotion and associated structures are no longer Kingdom Protozoa considered key characters in establishing the phylongeny (evolutionary relatedness) of Protista. Phylogeny is Complicated/Unresolved Alveolate Amoeboid Flagellated Protozoa Paramecium Protozoa Protozoa Ciliates EUGLENOZOA foramenifera PH CILIOPHORA dinoflagellate GRANULORETICULOSA trypanosomes (ciliates) (foramenifera) euglinids Euglenoid RADIOZOA DINOZOA trichomonads (dinoflagellates) (radiolarians) Giardia APICOMPLEXA ACANTHARIA (coccidians (actinarians) e.g. Plasmodium) Didinium HELIOZOA Amoeboid Flagellated (heliozoans) See pie chart ad taxonomic detail on pg 75 Protista and the Origin of Metazoans I. Protistan Body Plan is Characterized by Introduction -- Primarily unicellular I. Body Plan -- Small, 5 -300 µm A. S.A./Volume Constraint -- Lack organs B. Reynolds number (Lack a nervous system) II. Important Protists A. In food webs B. Agents of disease What constraints does the small unicellular body plan impose on the biology of protistans? III. Origin of Metazoans Evidence for colonial origin and metazoan ancestors S.A./Vol relationship imposes a limit on cell size As a cell increases in size, exchange with the environment Some Amebas becomes more difficult partly solve 1 this problem Inch L Surface Area ~ L2 (2.5 cm) Volume ~ L3 Therefore S.A./V declines L as L increases Cytoplasmic streaming provides continuous mixing or circulation of the cytosol 2 Small Size also affects scaling of physical forces Re = velocity x length of the organism Viscocity of Medium Balance of inertia and drag When Re is high, drag is relatively negligible on a moving organism (example, Re is 30,000 for a dragonfly in flight) Depends on the size and velocity of the organism When Re is low, drag forces dominate movement and on the viscocity of the medium. (example, Re for a protist could be <0.1) Expressed as Reynolds Number (Re) Re = velocity x length of the organism In what way would low Reynolds Viscocity of Medium numbers affect the ecology of protists? Re = vel x L Vis Re = velocity x length of the organism Viscocity of Medium What is life like at Low Reynolds numbers?? -- no inertia -- force of gravity balanced by viscocity -- yet ciliates travel 2 mm per sec. (8 body lengths) -- feeding also affected Vorticella feeding Re = vel x L I. Protistan Body Plan is Characterized by Vis -- Primarily unicellular -- Small, 5 -300 µm Viscous forces can -- Lack organs also be important in (Lack a nervous system) air but the medium is not very dense what conditions will What constraints does the small unicellular produce a low Re??? body plan impose on the biology of protistans? Midge 3 Anterior Organelles are the Food functional equivalents of vacuole organs. Oral nuclei groove Organelles not generally found in metazoans Cyto- - contractile vacuoles stome - trichocysts - toxicysts Fig 3.19 contractile Posterior http://www.youtube.com/watch?v=hSFJ- Paramecium Feeding vacuole Contraction spnn6c&NR=1 II. Importance of Protozoa Spasmin filaments The spasmoneme is a biological A. Major role in ecosystems as decomposers, food source for spring organelle. Contraction is metazoans completed in 2 ms at speeds up to 8 cm/sec and is triggered B. Responsible for a large number of human ailments, including by Ca++ activated interactions malaria, dysentery, sleeping sickness along the length of the supramolecular structure. The reaction does not require ATP C. Provided biologists with outstanding material for genetic, physiological and other studies. Protista and the Origin of Metazoans Metazoa arose from Protozoa sometime Introduction before the Cambrian 1200-600 mya I. Body Plan Which protozoan group was the ancestor?? A. S.A./Volume Constraint B. Reynolds number By what process was first metazoan formed?? II. Important Protists A. In food webs Are metazoans Monophyletic or Polyphyletic?? B. Agents of disease III. Origin of Metazoans What were the first Metazoans like?? Evidence for colonial origin and metazoan ancestors CAN WE EVER REALLY KNOW?? 4 3 Phyla are Possible Candidates as Basal Group of all Animals What is a “metazoan”?? Eukaryotic and multicellular Cell differentiation and coordination; more than a colony or aggregation of cells Cnidarians Layers of cells organized into “tissues” Sponges Embryonic development; gastrulation Flatworms Symbiotic Hypothesis Theoretically 3 ways in which a multicellular Colonial Hypothesis organism could evolve from a protist. Cellularization Hypothesis Strengths: Origin of Eukaryotes from prokaryotes Weakness: Genetic obstacles to reproduction. How do they integrate into a reproducing organism? Cellularization Stained Paramecium showing multiple ”inclusions” Macronucleus Strengths: Paramecium-flatworms are similar Weaknesses: no evidence of “compartmentalization” :flatworms with complex embryology :What about Cnidaria, Sponges ?? 5 Similarities of Choanocytes (sponge cells) and choanoflagellates (protozoan) (Haeckle’s favorite) Blastea Gastrea Strengths: models exist (Volvox, choanoflag.) : parallels animal embryology Weaknesses: ??? Choanocyte Choanoflagellate Model organization Eudorina Pandorina Choanoflagellates live as solitary and colonial forms Volvox Genetic Evidence (18S r-DNA) Opisthokonts share: uniflagellate (reproductive) stages with flagellum at the posterior Mitochondria with flattened, plate-like cristae 6 Based on sequence analyses of 5 proteins Monosiga has 86% sequence homology with animals. a. Phylogeny based on protein domain comparisons b-d. choanoflagellate cells bear a single Flagellum and an apical collar of actin- filled microvilli (bracket, c). D. an overlay of b-tubulin (reen), polymerized Mol. Biol. Evol. actin (red) and DNA (blue) localization 23: 93-106 2006 reveals the position of the flagellum within the collar of microvilli. Conclusions on Metazoan Origin Evidence best supports the colonial theory Choanoflagellate group is most likely ancestor; Evidence includes cell structure and genetic similarities Idea that metazoans are monophyletic is supported 7 .
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