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Home , Cellularization, Choanoflagellate, Didinium, Kingdom (biology), Paramecium, Protist

SEM of

Explain, in the context of , why there is more higher diversity (e.g. phyla) in the but a greater diversity on land. 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. some that they should be body plan classified as Kingdoms A. S.A./Volume Constraint

Explore the limitations of B. Reynolds number as a single cell - Among them are the II. Important ancestors of multicell Learn some of the ways in which protists are important A. In food webs including B. Agents of disease Evaluate evidence for the origin . of animals from ancestors

III. Origin of Metazoans Evidence for colonial origin and metazoan ancestors

Body plan characterized by: Most Common TYPES of Protista:

Ciliates ( Ciliophora): externally ciliated A. Unicellularity (most) B. Small Size (< 5-250 µm) Sarcodinids: 4 phyla of amoeboid types C. Lacking Organ Systems (, foramenifera, radiozoans, heliozoans) (including a nervous system) : 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 -Formers: Phylum and other very important parasitic forms

1 Means of locomotion and associated structures are no longer Kingdom considered key characters in establishing the phylongeny (evolutionary relatedness) of Protista. Phylogeny is Complicated/Unresolved

Alveolate Amoeboid Flagellated Protozoa Paramecium Protozoa Protozoa PH CILIOPHORA foramenifera GRANULORETICULOSA trypanosomes (ciliates) (foramenifera) euglinids Euglenoid RADIOZOA DINOZOA trichomonads () (radiolarians) APICOMPLEXA ACANTHARIA (coccidians (actinarians) e.g. ) 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

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 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

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Anterior are the Food functional equivalents of organs.

Oral nuclei groove Organelles not generally found in metazoans Cyto- - contractile stome - - 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 as decomposers, food source for spring . 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 , dysentery, sleeping sickness along the length of the supramolecular structure. The reaction does not require ATP C. Provided with outstanding material for genetic, physiological and other studies.

Protista and the Origin of Metazoans Metazoa arose from Protozoa sometime

Introduction before the 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 or aggregation of cells

Cnidarians Layers of cells organized into “tissues”

Sponges Embryonic development;

Flatworms

Symbiotic Hypothesis Theoretically 3 ways in which a multicellular Colonial Hypothesis organism could evolve from a protist. Cellularization Hypothesis

Strengths: Origin of from Weakness: Genetic obstacles to . How do they integrate into a reproducing organism?

Cellularization Stained Paramecium showing multiple ”inclusions”

Macronucleus

Strengths: Paramecium- are similar Weaknesses: no evidence of “compartmentalization” :flatworms with complex embryology :What about , ??

5 Similarities of ( cells) and (protozoan)

(Haeckle’s favorite)

Blastea

Gastrea

Strengths: models exist (, choanoflag.) : parallels embryology Weaknesses: ???

Model organization

Eudorina

Pandorina

Choanoflagellates live as solitary and colonial forms Volvox

Genetic Evidence (18S r-DNA)

Opisthokonts share: uniflagellate (reproductive) stages with at the posterior Mitochondria with flattened, plate-like cristae

6 Based on sequence analyses of 5 Monosiga has 86% sequence homology with animals.

a. Phylogeny based on comparisons

b-d. choanoflagellate cells bear a single Flagellum and an apical collar of - filled microvilli (bracket, c). D. an overlay of b- (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

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