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PROTISTA The paraphyletic, non-

fungi, non-animal, non-plant Eucarya

+ Even MORE new words

to remember!

Key Points

•  Origin of eukaryotes via symbiosis •  Origin of classification based on

functional (ecological) traits •  Current classification based on

phylogenetic principles •  Alternation of generations prominent

General

1.  Eukaryotes are mostly unicellular. 2.  Mixed history of classification: “Protista” an informal term of convenience for non-fungal, non-plant, non-animal eukaryotes.

3.  From amoeba to giant kelp, arranged functionally.

Functional arrangements

a.  Animal-like heterotrophic protists: Protozoa.

b.  Absorptive or fungus-like protists: Pseudopodians.

c.  Plant-like photosynthetic protists: Algae

d.  Mixotrophs

All of these groups are polyphyletic

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Protists are… 1.  …the earliest

Eukaryotes a.  True nucleus b.  Cytoplasmic organelles c.  ~2.2 bya

2.  …always associated with water, dampness, or body fluids

a.  Plankton, parasitic

Protists are…

3.  …aerobic (almost all) and have mitochondria for cellular respiration.

4.  …photoautotrophs, chemoheterotrophs, or both (mixotrophs). a.  Note NO

photoheterotrophs nor chemoautotrophs.

Protists are…

5.  …motile: most have flagella or cilia or pseudopodia at some stage.

6.  …asexual or truly sexual (true meiosis and mitosis)

flagella

The Origin of Eukaryotes “How to make a Eukaryote”

•  About 2.5 bya prokaryotes had diversified into many types.

•  But the small size and limited genome of prokaryotes constrained their evolution.

•  So how did Eukaryotes become possible?

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The Origin of Eukaryotes “How to make a Eukaryote”

•  Eukaryotic cell: true nucleus, cytoplasmic organelles –  Membrane-enclosed

structures with specialized function

–  Some with own genome (mitochondria, chloroplasts)

•  This compartmentalization allowed the evolution of larger cells. But how?

Endosymbiosis •  A sequence of events in

which specialized prokaryotes live within larger prokaryotes in symbiotic relationship.

•  Some became mitochondria and some chloroplasts.

•  Both were important in an increasingly aerobic world.

Ancestral A

rchaean &

evolution of nucleus

Aerobic α-proteobacterium è mitochondrion

Cyanobacterium è chloroplast

Eukaryotic chemoheterotroph

Eukaryotic photoautotroph

Endosymbiosis •  Model supported by

similarity in structure and RNA between certain prokaryotes and corresponding eukaryote organelles.

•  By alternative genetic code (DNA sequence translation to amino acids).

•  Mitochondria: α-proteobacteria are relatives.

•  Plastids (chloroplast and some non-photosynthetic): cyanobacteria are relatives.

Ancestral A

rchaean &

evolution of nucleus

Aerobic α-proteobacterium è mitochondrion

Cyanobacterium è chloroplast

Eukaryotic chemoheterotroph

Eukaryotic photoautotroph

Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Protist Diversity

•  Note that the vast majority of eukaryotic diversity is ‘protistan’ and unicellular.

•  Is “Protista” monophyletic, paraphyletic, or polyphyletic?

•  How does this phylogeny indicate that the difference between paraphyletic and polyphyletic is fuzzy?

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Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Protist Diversity

Protozoans •  Excavata I.  Alveolata II.  Opisthokonts (not

covered now) Algal Protists

IV.  Stramenopiles V.  Archaeplastids

Pseudopodians VI.  Rhizarians VII.  Amoebozoans

Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Protist Diversity

Protozoans •  Excavata I.  Alveolata II.  Opisthokonts (not

covered now) Algal Protists

IV.  Stramenopiles V.  Archaeplastids

Pseudopodians VI.  Rhizarians VII.  Amoebozoans

Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Protist Diversity

Protozoans •  Excavata I.  Alveolata II.  Opisthokonts (not

covered now) Algal Protists

IV.  Stramenopiles V.  Archaeplastids

Pseudopodians VI.  Rhizarians VII.  Amoebozoans

Excavata

•  Diplomonads •  Parabasalids •  Euglenozoans

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Excavata: Parasites •  Often anaerobic •  What eukaryotic

feature could be modified?

Giardia can be a severe intestinal parasite

Excavata: Parasites •  Diplomonads: •  Small, simple

mitochondria (mitosomes) –  Not involved in cellular

respiration –  Involved in maturation

of iron-sulfur proteins •  Two separate nuclei

–  Function unclear, NOT duplicated genomes Giardia can be a severe

intestinal parasite

Excavata: Parasites •  Parabasilids with

reduced mitochondria: hydrogenosomes –  Responsible for some

anaerobic metabolism

•  Anaerobic, flagellated protozoa

•  Include Trichomonas vaginalis, the most common protistan STD

Excavata: Euglenozoans •  All characterized by

spiral, crystalline rod inside flagella.

•  Kinetoplastids: –  Heterotrophs including

Trypanosoma –  Kinetoplastid: organelle

housing extraneous DNA •  Euglenids:

–  Often mixotrophs –  Photosynthesize in light –  Heterotrophic via

phagocytosis in dark

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Alveolata

•  What is its sister-clade? •  Members of the

Chromalveolata probably can photosynthesize because of the secondary endosymbiosis of a red alga.

•  Characterized by small, membrane-bound cavities, alveoli

Likely originated by secondary endosymbiosis

Figure 28.2

Cyanobacterium

Heterotrophic eukaryote

Primary endosymbiosis

Membranes are represented as dark lines in the cell.

1 2 3

One of these membranes was lost in red and green algal descendants.

Plastid

Red alga

Secondary endosymbiosis

Secondary endosymbiosis

Secondary endosymbiosis

Green alga

Dinoflagellates

Apicomplexans

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

Alveolata: Dinoflagellates •  Marine & freshwater

–  photosynthetic (~50%) phytoplankton

–  Some predators –  Some parasitic on fish

•  Most unicellular •  Cellulose “armor” and

paired flagella produce spinning movement.

•  Explosive population blooms result in red tides.

Alveolata: Dinoflagellates •  Zooxanthellae:

–  Important mutualists with corals (also jellyfish, clams, sea slugs, and other protists).

•  Obligate mutualism for many coral: –  provide carbohydrates via

photosynthesis, get protection.

•  Coral bleaching: –  Death or expulsion of

zooxanthellae leads to death of corals.

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Alveolata: Apicomplexans •  Parasites of animals •  Release tiny

infectious cells (sporozoites) that have specialized ability to penetrate into host cells and tissues.

•  Complex life history –  Sexual & Asexual

reproduction –  Often multiple hosts –  E.g. Plasmodium,

mosquitoes, and humans

Alveolata: Ciliates •  Move and feed by cilia. •  Very diverse group with

complex cells. –  Manage to be aggressive

predators and unicellular

•  Two types of nuclei: macronucleus and micronuclei (convert back and forth).

•  Asexual reproduction via mitosis and cytokinesis.

•  Sexual reproduction via meiosis and conjugation

Algal Protists •  Single-celled, colonial, or truly

multicellular (“seaweeds”) •  Freshwater or marine •  Important in aquatic food webs •  All have chlorophyll a (the primary

pigment) –  Accessory pigments: –  Carotenoids: yellow-orange –  Xanthophylls: brownish –  Phycobilin: red and blue

•  Account for 1/2 of global photosynthetic production

•  Various life cycles, but alternation of generations is key

Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Stramenopila •  Sister-clade to

Alveolates •  Hair-like projections on

flagellae •  Photoautotrophs

–  Chloroplasts derived from eukaryotic symbiont (recall 2’ endosymbiosis)

•  Oomycetes have lost chloroplasts and are heterotrophic

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Stramenopila: Diatoms (Bacillariophyta)

•  Olive-brown or yellow –  What pigments are

responsible for these?

Stramenopila: Diatoms (Bacillariophyta)

•  Olive-brown or yellow –  Xanthophylls &

carotenoids

•  Freshwater & marine •  Distinctive cell structure

based on silica wall matrix.

•  Excellent index fossils. •  Form massive

sediments.

Stramenopila: Brown algae (Phaeophyta)

•  Carotenoids; xanthophylls •  Why do so many marine

photosynthesizers use auxiliary pigments?

•  Marine, multicellular. •  Common in cool coastal

water. •  Some giant (100m) have

fastest linear growth of any organism (60m/season); e.g. Macrocystis, giant bladder kelp.

Stramenopila: Brown algae (Phaeophyta)

•  Truly multicellular thallus, independently derived separate tissue specialization: –  Holdfast: rootlike anchor –  Stipe: stemlike structure –  Blades: leaflike structure

where majority of photosynthesis occurs

•  True alternation of generations

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Alternation of Generations •  Life cycles in which

both haploid and diploid stages are multicellular.

•  Also evolved independently in plants and fungi.

•  Divided into haploid gametophyte generation and diploid sporophyte generation

Stramenopila: Oomycetes •  Water molds, white rusts,

mildews •  Heterotrophs, lack

chloroplasts •  Important in organic

decomposition in aquatic environments

•  Some (especially mildews) harmful plant pathogens. –  Potato blight Phytophthora

infestans

Archaeplastids (the non-plant ones)

•  Rhodophyta (Red Algae) •  Chlorophyta (Green Algae)

Archaeplastids: Red Algae (Rhodophyta)

•  (not all red, red to black). •  Multicellular, most marine

(some fresh). •  Abundant in warm coastal

tropics. •  Some in very deep water (ca

250m). •  No flagellated stages in life

cycle. •  Chloroplasts from primary

cyanobacteria symbiont.

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Archaeplastids: Green Algae (Chlorophyta)

•  7,000 species, most diverse Protista after diatoms.

•  Shared common ancestry with plants.

•  Like red algae, chloroplasts from primary cyanobacteria symbiont. –  Synapomorphy of Archaeplastids

•  Mostly unicellular •  Mostly fresh water

Chlamydomonas, a single-cellular freshwater green alga

Green algae life histories •  But have quite a diversity

in life history •  Can inhabit damp soils. •  Can live symbiotically with

protozoa, invertebrates, fungi

•  Note that lichens can also be associations between fungi and cyanobacteria or brown algae or yellow-green algae (a stramenopile we didn’t cover)

Green algae life histories

•  Larger size and greater complexity evolved by three different mechanisms: 1.  Colony formation (e.g.

Volvox in pond scum) 2.  True multicellularity,

complete with alternation of generations (e.g. the sea lettuce, Ulva)

3.  Supercellularity: repeated division of nuclei with no cytoplasmic division, similar to fungal hyphae or slime molds (e.g. in Caulerpa)

Diplomonads

Parabasalids

Euglenozoans

Excavata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“SAR

” clade

Stramenopiles

Alveolates

Rhizarians

Green

algae

Red algae

Chlorophytes

Charophytes

Land plants

Archaeplastida

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Unikonta

Choanoflagellates

Animals

Am

oebozoans O

pisthokonts

Pseudopodians

•  Eukaryotes with Pseudopodia that move and feed by cellular extensions.

•  Pseudopodia is a generic term for extensions that can bulge from any portion of the cell.

•  Much like “wing”, this does not indicate homology.

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Rhizarians

•  Originally united by DNA sequence data. •  Pseudopodia are threadlike.

Rhizaria: Foraminiferans “Forams”

•  All marine, primarily in sand, attached to algae, or occur as plankton.

•  Encased in multichambered, coiled, snail-like shells (tests) made of Calcium Carbonate (CaCO3) –  More than 90% of known

diversity are from fossils –  Deposition of CaCO3 tests

creates limestones and chalks. •  Cytoplasm can be uninucleate or

multinucleate and extends through tests as pseudopodia.

•  Some tests >5cm in diameter.

Rhizaria: Radiolaria •  “ray feet” or axopodia:

numerous slender pseudopodia reinforced by microtubules.

•  Used for flotation and feeding: food sticks to axopods, engulfed and transported by cytoplasm

•  Important component of plankton: –  Heliozoans in freshwater –  Radiolarians in marine

•  Shells of silica often deposited in sediments

Amoebozoans •  “root-like foot” •  Pseudopodia are lobe- or tube-shaped •  Simple, naked, or shelled •  Unflagellated cells that move via pseudopodia and feed

by surrounding and engulfing food (phagocytosis) •  Sister group of lineages including fungi and animals

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Amoebozoans : Gymnamoebas & Entamoebas •  More typical amoebas. •  Gymnamoeba:

–  Free-living heterotrophs on bacteria or detritus.

•  Entamoebas: –  All parasitic; –  No meiosis, reproduce

using various asexual modes

–  Include Entamoeba histolytica, responsible for amoebic dysentery

Amoebozoans: Slime Molds (Mycetozoans)

•  Superficially resemble fungi •  In cellular organization and reproduction

are obviously amoebozoans.

Plasmodial slime molds (Myxomycota)

•  All heterotrophs, often brightly colored.

•  Feeding stage is a large amoeboid mass called the plasmodium (!). –  Not multicellular, but

multinucleated. –  Via the process of

coenocytosis: repeated division of nuclei without cytoplasmic division.

Plasmodial slime molds: “Alternation of generations”

Environmental stress

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Cellular slime molds (Acrasiomycota)

•  Aggregates of individual cells that keep their identity while feeding.

•  Haploid. •  NOT coenocytic. •  Reproduce asexually with

fruiting bodies. •  Reproduce sexually as

giant cell (grows via consuming other haploid amoebas).

•  Probable inspiration for scene from Terminator 3

Comparative Biology & Cellular Slime molds

•  Researchers at UCSD studying Dictyostelium, a cellular slime mold, found that two genes used to guide the amoeba to food sources are also used used to guide human white blood cells to the sites of infections.