MODULE 6 Protistan Diversity

The Old Five-Kingdom Model

Whittaker (1969)

In this model Protista = all single-celled eukaryotes

DNA Sequencing: The Molecular Evidence

Evidence That Broke Protista

Green algae share more DNA with land plants than with amoebas.

DNA Sequencing: The Molecular Evidence

Evidence That Broke Protista

Choanoflagellates share more DNA with animals than with diatoms.

DNA Sequencing: The Molecular Evidence

Evidence That Broke Protista

Slime molds share more DNA with Amoebozoa than with fungi.

DNA Sequencing: The Molecular Evidence

Evidence That Broke Protista

Many protists are more closely related to plants, animals, or fungi than they are to one another

DNA made it clear: Protista was not a natural evolutionary group.

Ultrastructure

Evidence That Broke Protista

• Stramenopiles have a hairy flagellum.

• Alveolates have cortical alveoli beneath the membrane.

• Amoebozoa have lobose pseudopodia

• Rhizaria have filose pseudopodia and mineralized tests

• Plastids differ in the number of membranes, Ultrastructure revealing distinct endosymbiotic origins.

• Stramenopiles

• Alveolates

Evidence That Broke Protista - Ultrastructure

• ______________ have a hairy flagellum.

• ______________ have cortical alveoli beneath the membrane.

• Amoebozoa

• Rhizaria

Evidence That Broke Protista - Ultrastructure

• ______________ have lobose pseudopodia

• ______________ have filose pseudopodia and mineralized tests

Ultrastructure

Evidence That Broke Protista

This meant that protists were not “simple” or “primitive”—they were structurally diverse in ways that reflected deep evolutionary splits.

Evolutionary Relationships

Evidence That Broke Protista

• Green algae closer to plants

• Choanoflagellates closer to animals

• Slime molds ≠ fungi

• nucleus; ER; Golgi

• Cytoskeleton

The First Eukaryotes

• 1.8–2.1 billion years ago

• Internal membranes, _________, ___, ______

• ____________ for phagocytosis and movement

mitochondria

The _____________ formed when an ancestral eukaryote consumed aerobic bacteria.

Evidence for “Mitochondria: The First Symbiosis”

Primary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

Cells involved - Eukaryotic cell engulfs another living prokaryote

Secondary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

Cells involved - Eukaryotic cell engulfs another eukaryotic cell that has undergone primary endosymbiosis

Primary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

• Occurrence - first

• Dependence - Cells are independent of one another

Secondary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

• Occurrence - later

• Dependence - Smaller cell depends on the larger cell

Primary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

Result - Formation of the first membrane, which belongs to the smaller cell

Secondary Endosymbiosis

State whether this description is for primary or secondary endosymbiosis.

Result - Formation of the three plasma membranes, where the second membrane belongs to the first eukaryotic cell, and the third membrane belongs to the second eukaryote

Protists are found almost everywhere—ranging from freshwater, marine environments, and damp soil to extreme habitats like snow, hot springs, and the digestive tracts of animals—due to their incredible metabolic, morphological, and ecological adaptability. Their pervasive distribution across diverse habitats is largely explained by multiple endosymbiotic events, which allowed them to acquire new functionalities (such as photosynthesis) and diversify, and their high adaptability, allowing them to fit into various ecological niches.

unicellular

multicellular; colonial

Protists are Mostly ____________

Some ____________ or _____________

Modes of Movement

• Flagella

• Cilia

• Pseudopodia

Modes of Movement

• ________________

• ________________

• ________________

Life Cycles

• Asexual (binary/multiple fission)

• Sexual reproduction under stress

• Alternation of generations in some groups

Life Cycles

• Asexual (______________)

• Sexual reproduction under stress

• Alternation of generations in some groups

How were the protist supergroups determined?

1. Molecular phylogenetics

2. Ultrastructure

3. Endosymbiosis

4. Life cycles

5. Ecology

How were the protist supergroups determined?

1. _________________

2. _________________

3. _________________

4. _________________

5. _________________

Archaeplastida

Which protist supergroup does this describe?

• Primary plastids

• Cellulose walls

Archaeplastida

Which protist supergroup does this describe?

• Starch storage

• Glaucophytes retain peptidoglycan layer

Archaeplastida

Which protist supergroup does this describe?

Ecological Roles

• Oxygen production

• Red algae in reef building

Amoebozoa

Which protist supergroup does this describe?

• Lobose pseudopodia

• Phagocytosis

Amoebozoa

Which protist supergroup does this describe?

Soil predators, decomposers

Amoebozoa

Which protist supergroup does this describe?

Slime molds

• Unicellular multicellular transitions

• Aggregative behavior

Amoebozoa

Which protist supergroup does this describe?

Opisthokonta

Which protist supergroup does this describe?

Animals + fungi + protist relatives

Posterior flagellum

Opisthokonta

Which protist supergroup does this describe?

Choanoflagellates resemble sponge collar cells

Opisthokonta

Which protist supergroup does this describe?

Opisthokonta

Which protist supergroup does this describe?

Opisthokonta

Which protist supergroup does this describe?

SAR

Which protist supergroup does this describe?

• Stramenopila, Alveolata, and Rhizaria

• Strong molecular support

• Extremely diverse

SAR - Stramenopila

Which protist supergroup does this describe?

Hairy flagellum

SAR - Stramenopila

Which protist supergroup does this describe?

• Diatoms (silica frustules)

• Brown algae (kelp forests)

• Oomycetes (decomposers/parasites)

SAR - Alveolata

Which protist supergroup does this describe?

Cortical alveoli

SAR - Alveolata

Which protist supergroup does this describe?

• Dinoflagellates (red tides, bioluminescence)

• Apicomplexans (Plasmodium)

• Ciliates (dual nuclei)

SAR - Rhizaria

Which protist supergroup does this describe?

Filamentous pseudopodia

SAR - Rhizaria

Which protist supergroup does this describe?

• Forams (CaCO₃ tests)

• Radiolarians (silica skeletons)

Excavata

Which protist supergroup does this describe?

Feeding groove

Excavata

Which protist supergroup does this describe?

Modified mitochondria (mitosomes, hydrogenosomes)

Excavata

Which protist supergroup does this describe?

Flexible pellicle

Excavata

Which protist supergroup does this describe?

• Mixotrophs (Euglena)

• Parasites (Giardia, Trypanosoma)

Stramenopila

Alveolata

What are the two groups previously known as Chromoalveolata?

Protists as Primary Producers

Which Ecological & Human Impact?

• Diatoms + dinoflagellates = ~50% of global photosynthesis

• Base of aquatic food webs

Symbiosis: Coral & Zooxanthellae

Which Ecological & Human Impact?

• Nutrient exchange

• Coral bleaching when symbiosis breaks down

Protists as Decomposers

Which Ecological & Human Impact?

• Oomycetes

• Slime molds

• Nutrient recycling

Protists as Pathogens

Which Ecological & Human Impact?

• Plasmodium → malaria

• Trypanosoma brucei → sleeping sickness

• Naegleria fowleri → encephalitis

• Entamoeba histolytica → amoebiasis