"Protists" and the origins of
Animalia

History of Ideas about Major Divisions of Life

• 1866: Haekel -- Divided Protistans (all one celled organisms) vs. Multicellular
  • Early-mid-1900s: Better optics and biochemistry, differences between prokaryotic (simple 1-strand circular DNA, lack nuclear membrane, organelles) and eukaryotic cells (double strand DNA, complex chromosomes, mitosis, nucleus--see handout)
• 1969 - Whittaker - 5 kingdoms
  • Kingdom Monera (prokaryotic bacteria and blue green algae)
  • Kingdom Protista (unicellular eukaryotic organisms)
  • Kingdom Plantae (multicellular eukaryotic photosynthesizing higher plants and algae)
  • Kingdom Fungi (multicellular eukaryotic molds, yeasts, and fungi; obtain food by absorption)
  • Kingdom Animalia (multicellular eukaryotic invertebrates and vertebrates that mostly ingest their food (some are parasitic and absorb food)
  • 1990 - Woese, Kandler, Wheelis - nucleotide sequences of ribosomal RNA : 3 domains
    • Bacteria (true bacteria)
    • Archaea (differ in membrane structure and RNA sequences from bacteria; includes "extremophiles")
    • Eucarya (all eukaryotes)

Eucarya (Woese et al. 1990)

• Protista (not monophyletic group; is paraphyletic because does not contain all descendants of its most recent common ancestor).
• If the phylogenetic tree in Fig. 3-9 (see handout) is supported by further evidence, it will be necessary to classify as Kingdoms Ciliata, Flagellata, Microsporidia (Apicomplexa)...

Eucarya (Woese et al. 1990)

• Protistans (several kingdoms?)
• Kingdom Plantae
• Kingdom Fungi
• Kingdom Animalia

The Emergence of Eukaryotes: "Protists" as ancestors

Origin of eukaryotes

• Probably through symbiosis
• Anaerobic and aerobic bacteria present
• Some bacteria able to photosynthize to create their own CHO, releasing oxygen into the environment, making conditions difficult for the many anaerobic bacteria

• Anaerobic bacteria may have engulfed aerobic bacteria, who had enzymes for obtaining energy in presence of oxygen -- became ancestors of mitochondria
• Other bacteria may have engulfed photosynthetic bacteria in order to acquire ability to photosynthesize -- became ancestors of chloroplasts

"Protists" are a grade

• Protists are a heterogeneous group of Eukaryotes (probably multiple origins)...
• Nucleus
• Chromosomes
• 9(2)+2 flagella/cilia
• Organelles
• (see review of key characteristics on p. 69)

Why "protists" are important

• Important disease organisms for humans and other organisms
  • E.g., Malaria, "sleeping sickness", toxoplasmosis, Pfeisteria, Giardia, Red tide, etc.
• Insights into origin of animals

General "Protist" Characteristics

• Cilia/Flagella
• Cilia and Flagella have the same basic design
• 9(2) + 2
• Microtubules slide past each other

General "Protist" Locomotion

• Cilia/Flagella
• Corkscrew motion
  • boat propellar - push forward
  • airplane propellar - pull forward
• May be organized in patches, groups, sheets, membranelles

General "Protist" Locomotion

• Cilia/Flagella
• Pseudopodia
• Ectoplasm (gel) vs. Endoplasm (sol)
• Figure 4-3

General "Protist" Feeding

• Feeding highly variable
• Autotrophs
  • Synthesize energy-rich compounds
  • Photosynthetic

General "Protist" Feeding

• Feeding highly variable
• Autotrophs
• Heterotrophs
  • Engulf prey - Phagocytosis
  • Sticky pseudopods, axopods
  • Use cilia to generate a feeding current

General "Protist" Reproduction

• Again, highly variable
• Asexual by Fission
• Mitosis, offspring identical
• May be binary (longitudinal or transverse, 2 offspring) or multiple (many offspring, common in parasites)
• Figures 4-8, 9

General "Protist" Reproduction

• Asexual by Fission
• Sexual
  • Syngamy - meiosis: haploid cells form, one cell fertilized by haploid cell from another individual

General "Protist" Reproduction

• Asexual by Fission
• Sexual
  • Syngamy (vs. autogamy: meiosis but haploid cells from same parent cell unite)
  • Conjugation
    • Macronucleus - metabolic, synthetic, developmental
    • Micronucleus - reproductive, exchange genetic material

We'll consider three Phyla

• Phylum Sarcomastigophora
  • Subphylum Mastigophora - Flagellates
    • Class Phytomastigophora - "plant-like"
    • Class Zoomastigophora - "animal-like"
  • Subphylum Sarcodina - Amoebas, etc.
• Phylum Ciliophora - Ciliates
• Phylum Apicomplexa - many parasites
  • Sporozoea (malaria, toxoplasmosis)
  • Microsporidia
    • Microsporidia

Phylum Sarcomastigophora

• Move with flagella and/or pseudopodia
• Only one type of nucleus
• Sexual reproduction, if present, by syngamy
• Two major sub-phyla
  • Mastigophora, Sarcodina

Subphylum Mastigophora

• Have one or more flagella
  • Push like a boat propeller or
  • Pull like an airplane propeller
• Often reproduce asexually by longitudinal binary fission
• Two classes
  • Phytomastigophora
  • Zoomastigophora

Class Phytomastigophora

• Free living, 1 or 2 flagella
• Most autotrophic (photosynethesize, chloroplasts) (e.g., Euglena)
  • Include dinoflagellates (red tides, zooxanthellae in corals)
• But some are colorless (lack chloroplasts), absorb nutrients, or phagocytize whole particles or organisms (e.g., Peranema)

Class Zoomastigophora

• Free living or symbiotic (never autotrophic), may be colonial
• May have 1 or many flagellae
• Many are parasitic
  • Kala azar - circulatory system and skin
  • Chagas' disease - muscles, heart, nerves
  • Sleeping sickness (trypanosoma) - brain
• Often asexual, multiple fission
• Includes Choanoflagellates - often colonial, similar to collar cells of sponges

Subphylum Sarcodina

• Usually move via pseudopodia
• Trend towards evolution of tests
• Primitive ones (e.g., Amoeba) use pseudopodia for feeding and locomotion
• More advanced are armored, planktonic
  • Pseudopodia not used for locomotion
  • Instead form adhesive traps

Subphylum Sarcodina

• Some primitive amoeboid forms also have a flagellum; some (e.g., Pfeisteria) may have both and also alternate between primarily amoeboid and primarily flagellated life stages, often with resistent cysts in their life cycle as well.

Phylum Ciliophora

• Morphologically complex - two types of nuclei
• One macronucleus
• One or more micronuclei
• Move and feed with cilia
• Usually bilaterally symmetrical (this will be important later)

Ciliophoran trends

• Carnivory to suspension feeding (e.g., Stentor)
• Complex buccal cavity, shift from anterior to side
• Specialized cilia and ciliar fields (may be fused into membranelles)

Phylum Apicomplexa

• All internal parasites (many host phyla)
• Unique apical complex
  • Microneme and rhoptries [see fig.4-17] self-replicating, with own circular single strand DNA
  • Possible bacterial origin like mitochondria, chloroplasts with enzymes similar to those of bacteria and plants but not animals
  • Used to recognize and penetrate host

Phylum Apicomplexa

• Locomotion
  • Pseudopods in some stages
  • Some have flagellated gametes
  • Some move with waves of contraction
• Reproduction
  • Asexual (usually multiple fission, often in 2nd host)
  • Sexual (some undergo meiosis after fertilization, and all offspring produced by mitosis are haploid until gametes form a zygote again in the life cycle --

Phylum Apicomplexa

• Reproduction
  • Asexual
  • Sexual (some undergo meiosis after fertilization, and all offspring produced by mitosis are haploid until gametes form a zygote again in the life cycle -- this is common in plants, and we will see this in some multicellular invertebrate phyla such as Rotifers
  • Often resistant spores (infective)
• Class Sporozoa
• Class Microsporidia

Class Sporozoa

• Plasmodium - malaria
• Toxoplasma - toxoplasmosis (birth defects)
• Coccidians - epithelial tissues

Plasmodium - malaria

• 100 million cases/yr - 1 million deaths/yr
• Carried by mosquito -- review life cycle on handout and in text (especially note biology and hosts during sexual and asexual phases)

Plasmodium - malaria

• Increasing problem: mosquitos more resistant to insecticides, plasmodium more resistant to drugs
• Most promising biotechnology research: Drugs that affect apical complex, which is necessary for sporozoites and merozoites to locate and penetrate cells

Origin of animals - Two theories

• Syncytial theory
  • Animals evolved from a multinucleate protociliate
• Colonial theory
  • Animals evolved by ingression from hollow, spherical, colonial flagellates

Syncytial Theory

• Metazoa evolved from multinucleate ciliates
• Based on
  • Multinucleate ciliates
  • Bilaterality in ciliates
• How?

Syncytial Theory

• Metazoa evolved from multinucleate ciliates
• Based on
  • Multinucleate ciliates
  • Bilaterality in ciliates
• How?
  • Cellularization -> Differentiation

Syncytial Theory

• Problems include
• Radial symmetry in "Radiates"
• No evidence of cellularization in basal metazoans
• Doesn't explain metazoan flagella

Colonial Theory

• Metazoa evolved from colonial flagellates
• Based on
  • Colonial tendency in flagellates
  • Presence of flagella in multicellular organisms
• How?

Colonial Theory

• Metazoa evolved from colonial flagellates
• Based on
  • Colonial tendency in flagellates
  • Presence of flagella
• How?
  • Specialization of cells within a colony

Support for Colonial Theory

• Flagellated sperm widespread in animals
• Colonial tendency in flagellates
• Shape of mitochondrial christae (Sarcomastigophora flat, Ciliophora tubular)
• Molecular evidence indicating a close relationship between flagellates and metazoans
• Similarity between Choanoflagellates and Choanocytes of sponges.

Choanoflagellates and Choanocytes