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