1. General Features of Protists 2. Survey of the Protista Chapter... · 1. General Features of Protists 2. Survey of the Protista A. The Excavata ... Red alga Green alga Primary ...

Chapter 28: Protists

1. General Features of Protists

2. Survey of the ProtistaA. The Excavata

B. The SAR Clade

C. The Archaeplastida

D. The Unikonta

1. General Features of Protists

All Protists are Eukaryotes

Eukaryotic organisms consist of 1 or more eukaryotic cells:Prokaryotic cell

Nucleus

Eukaryotic cell Organelles

• eukaryotic cells contain a “true nucleus” and other membrane-bound organelles

Most eukaryotes are single-celled organisms, most of which are protists(i.e., not fungi, plants or animals).

Protists have Diverse Characteristics

Protists are much more diverse that plants, animals & fungi:

• most are unicellular, though some are multicellular

• some are photoautotrophs (commonly called “algae”)

• protists can reproduce sexually, asexually, or both

• some are chemoheterotrophs (commonly called “protozoa”)

• some have characteristics of both (mixotrophs)

Endosymbiosis in Eukaryotic EvolutionPlasma membrane

DNA

Cytoplasm

Ancestral

prokaryote

Nuclear envelope

Nucleus Endoplasmic

reticulum

Aerobic heterotrophic

prokaryote

Mitochondrion

Ancestral

heterotrophic eukaryote

Photosynthetic

prokaryote

Mitochondrion

Plastid

Ancestral photosynthetic

eukaryote

The endosymbiont theory proposes

that mitochondria & chloroplasts are

derived from internalized prokaryotes.

Cyanobacterium

Nucleus

Membranes

are represented

as dark lines

in the cell.

1 23

Heterotrophic

eukaryote One of thesemembraneswas lost inred andgreen algaldescendants.

Red alga

Green alga

Primary

endosymbiosis

Secondary

endosymbiosis

Dinoflagellates

Plastid

Stramenopiles

Plastid

Euglenids

Chlorarachniophytes

Secondary

endosymbiosis

Secondary

endosymbiosis

A Closer Look at Plastid Evolution

Protists No Longer Constitute a Single Kingdom

The traditional grouping of eukaryotes involved 4 kingdoms:

PROTISTA

FUNGI

PLANTAE

ANIMALIA

However this is not consistent with phylogenies based on recent molecular analysis which supports the following 4 supergroups…

Diplomonads

Parabasalids

Euglenozoans

Excav

ata

Diatoms

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

“S

AR

” c

lad

e

Stra

men

op

iles

Alv

eo

late

sR

hiz

aria

ns

Gre

en

alg

ae

Red algae

Chlorophytes

Charophytes

Land plants

Arc

haep

lastid

a

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Un

iko

nta

Choanoflagellates

Animals

Am

oeb

ozo

an

sO

pis

tho

ko

nts

Figure 28.2

Giardia intestinalis,

5 μm■ Excavata

Diatom diversity

50 μm■ “SAR” Clade

Volvox, a colonial freshwater green alga

50 μm■ Archaeplastida

A unikont amoeba

100 μm

■ Unikonta

4 SupergroupsThe evolutionary

history of all eukaryotes

currently consists of 4 supergroups:

1. Excavata

2. SAR Clade

3. Archaeplastida• includes all land plants

4. Unikonta• includes fungi & animals

All eukaryotes that are not plants, animals or fungi are considered to be Protists.

2A. Survey of the Protista

The Excavata

Diplomonads

Parabasalids

Euglenozoans

SAR clade

Archaeplastida

Unikonta

Excavata

General Characteristics of Excavates

Below are some of the characteristics seen in Excavates:

• some members have an “excavated” feeding groovesthat are associated with unique cytoskeletal structures

• many have modified “unclassical” mitochondria

• most have 2 or more flagella

• includes the following major groups:

DIPOMONADS PARABASALIDS EUGLENOZOANS

Diplomonads

Diplomonads have reduced mitochondria called mitosomes and derive energy by anaerobic processes. They also have 2 nuclei and multiple flagella.

Many are parasites such as Giardia intestinalisshown here:

Flagella

Undulating

membrane 5 μm

Parabasalids

Parabasalids have reduced mitochondria called hydrogenosomes and thrive in anaerobic environments.

• Trichomonas vaginalis, a sexually transmitted human pathogenshown below is one example

Flagella

8 μm

0.2 μm

Crystalline rod

(cross section)

Ring of microtubules

(cross section)

Euglenozoans

The Euglenozoa is a diverse clade that includes predatory heterotrophs,photosynthetic autotrophs, mixotrophs, and parasites.

• a characteristic feature of this clade is the crystalline rod structure within their flagella

• members of this clade include:

KINETOPLASTIDS

EUGLENIDS

9 μm

Kinetoplastids

Kinetoplastids have a single mitochondrion containing an unusual organized mass of DNA called a kinetoplast.

• includes the genus Trypanosomawhich contains parasites that cause “sleeping sickness” and Chaga’s disease

RBC

Long flagellum

5 μm

Eyespot

Short flagellum

Contractile vacuole

Nucleus

Chloroplast

Plasma

membrane

Light

detector

PellicleEuglena (LM)

EuglenidsEuglenids have 1 or 2 flagella, and some members of this clade, such as the genus Euglena, are both autotrophic and heterotrophic (i.e., mixotrophs).

2B. Survey of the Protista

The SAR Clade

Diatoms

SA

R c

lad

e

ArchaeplastidaUnikonta

Excavata

Golden algae

Brown algae

Dinoflagellates

Apicomplexans

Ciliates

Forams

Cercozoans

Radiolarians

Stramenopiles

Alveolates

Rhizarians

General Characteristics of the SAR Clade

The SAR clade is a highly diverse monophyletic supergroupbased on DNA similarities that includes the following:

STRAMENOPILES

ALVEOLATES

RHIZARIANS

Smooth

flagellum

5 μm

Hairy

flagellum

Stramenopiles

Most members of the Stramenopile clade have both “hairy” and smooth flagella.

• this clade includes the following ecologically important groups of photosynthetic organisms:

DIATOMS

GOLDEN ALGAE

BROWN ALGAE

40 μ

m

Diatoms

Diatoms have unique glass-like walls made of silicon dioxide and are a significant portion of phytoplankton in the oceans.

• their remains are the main components of white sediments referred to as “diatomaceous earth” (e.g., the “white cliffs of Dover”)

Flagellum

25 μm

Outer container

Living cell

Golden Algae

• contain yellow and brown carotenoids which give them their characteristic color

• typically have two flagella

• most are single-celled though some are colonial

Blade

Stipe

Holdfast

Brown Algae

Brown algae are all multicellular and are the largest algae.

• includes many “seaweeds” such as kelp

• although brown algae are not plants, many have plant-like structures shown in this image

Haploid (n)

Diploid (2n)

Sporangia

MEIOSIS

Sporophyte

(2n) Zoospore

Gameto-

phytes

(n)

Female

Male

Sperm

Egg

Zygote

(2n)Mature female

gametophyte

(n)

Developing

sporophyte

FERTILIZATION

10 cm

Alternation ofGenerations

• many multicellular algae have a life cycle similar to that of plants called the “Alternation of Generations” – the alternation between multicellular haploidand diploid forms

Flagellum Alveoli

Alveolate0.2

μm

Alveolates

Members of the Alveolate clade have membrane enclosed sacs called alveoli must beneath the plasma membrane.

• this clade includes the following:

DINOFLAGELLATES

APICOMPLEXANS

CILIATES

Flagella

3 μm

(a) Dinoflagellate

flagella

(b) Red tide in the Gulf

of Carpentaria in

northern Australia

Dinoflagellates

Dinoflagellates are also an important component of phytoplankton and have 2 flagella, one of which wraps around the cell and causes it to rotate.

• are responsible for the algal blooms known as “red tides”

Apicomplexans

The Apicomplexans are parasites of animals that have complex life cycles with multiple hosts.

• the most significant genus in this clade is Plasmodium, the cause of malaria

• nearly 1 million people each year die from malaria

Merozoite

0.5 μm

Apex

Red blood

cell

Haploid (n)

Diploid (2n)

Sporozoites

(n)

Inside mosquito Inside human

Liver

Liver

cell

Red

blood

cells

Merozoite

(n)

Game-

tocytes

(n)

Gametes

Zygote

(2n)

Oocyst

MEIOSIS

FERTILIZATION

PlasmodiumLife Cycle

• mosquitoes are the definitive host (in which sexualreproduction occurs)

• humans are the intermediate host (in which reproduction is asexual)

Contractile

vacuole

50 μmCilia

Micronucleus

Macronucleus

Oral groove

Cell mouth

Food

vacuoles

(a) Feeding, waste removal, and water balance.

Ciliates

The Ciliates clade is a large group characterized by cilia used for locomotion and/or feeding and 2 nuclei, one macronucleus and one micronucleus.

• the genus Paramecium is a good example

• Ciliates also engage in a form of sexual reproduction called conjugation…

Compatible

mates

(b) Conjugation and reproduction.

MEIOSIS

The original macro-nucleus disintegrates.

Haploid

micronucleus

MICRO-

NUCLEAR

FUSION

Conjugation

Asexual

reproduction

Diploid

micronucleus

Diploid

micronucleus

Conjugation in Ciliates

Rhizarians

The Rhizarians are mostly amoebas containing pseudopodia that are threadlike (unlike the Amoebozoa in the Unikonta clade.

• this clade includes the following:

RADIOLARIANS

FORAMS

CERCOZOANS

Pseudopodia

200 μm

Radiolarians

Radiolarians have delicate, symmetrical endoskeletons made typically of silica.

• the pseudopodia extend from the cell to catch prey

Forams

Foraminiferans (“hole bearers”), or forams for short, are single-celled heterotrophs that characteristically have multi-chambered shells called tests.

• foram tests are found throughout the fossil record and their tests can be analyzed to estimate ocean temperatures in ancient times

Chromatophore

5 μm

Cercozoans

• most are heterotrophs, though a few such as Paulinellachromatophora are autotrophs that contain unique photosynthetic structures called chromatophores

Chlorophytes

SAR clade

Arc

haep

las

tida

Unikonta

Excavata

Charophytes

Red algae

Green algae

Land plants

2C. Survey of the Protista

The Archaeplastida

The Archaeplastida

The supergroup Archaeplastida contains the following:

• molecular and other data indicate the land plants are descendants of the green algae, though only the red and green algae are considered to be protists

RED ALGAE

GREEN ALGAE

LAND PLANTS

▼ Nori

8 mm

20 cm

◀ Dulse (Palmaria palmata)

► Bonnemaisonia

hamiferaRed Algae

The red algae contain, in addition to chlorophyll, a red accessory pigment called phycoerythrin.

• phycoerythrin absorbs non-red light

• many red algae live in deep water where red light does not penetrate

This group includes many seaweeds some of which are edible.

(a) Ulva, or sea lettuce

(b) Caulerpa, an

intertidal

chlorophyte

2 cm

Green Algae

Green algae contain green chloroplasts (due to chlorophyll) and includes 2 main groups:

CHAROPHYTES

CHLOROPHYTES

• closest relatives to plants

• most live in fresh water

Haploid (n)

1 μm

Diploid (2n)

Flagella

Cell wall

Nucleus

Cross

section

of cup-

shaped

chloroplast(TEM)

Zoospore

ASEXUAL

REPRODUCTION

Gamete

(n)

Mature cell

(n)

Zygote

(2n)

FERTILIZATION

MEIOSIS

+

+

+

+

−

−

−

−

SEXUAL

REPRODUCTION

Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages:

Chlorophyte Life Cycle

SAR clade

Archaeplastida

Un

iko

nta

Excavata

Slime molds

Tubulinids

Entamoebas

Nucleariids

Fungi

Choanoflagellates

Animals

2D. Survey of the Protista

The Unikonta

Am

oe

bo

zoa

Op

isth

oko

nts

The Unikonta

This group contains 2 major clades:

• all of which are protists:

• includes animals and fungi in addition to some protists:

AMOEBOZOA

OPISTHOKONTS

SLIME MOLDS TUBULINIDS ENTAMOEBAS

NUCLEARIIDS CHOANOFLAGELLATES

Amoebozoans

Amoebozoans have tube or lobe-shaped pseudopodia (unlike the Rhizaria).

Amoeba proteus, a tubulinid Entamoeba histolytica

Slime Molds

Cellular slime molds form multicellular aggregates in which cells are separated by their membranes.

• cells feed individually and can aggregate to migrate and form a fruiting body

Plasmodial slime molds form multicellular aggregates in which there is no separation of nuclei by membranes (i.e., a plasmodium), thus they are not considered to be multicellular.

• species such as Dyctiostelium discoideum are studied to better understand the origins of multicellularity

Haploid (n)

200 μm

600 μm

Diploid (2n)

Spores

(n)

Emerging

amoeba (n)

Solitary amoebas

(feeding stage)

(n)

Fruiting

bodies

(n)

ASEXUAL

REPRODUCTION

Aggregated

amoebas

Migrating

aggregate

SEXUAL

REPRO-

DUCTION

Zygote

(2n)

Amoebas

(n)

FERTILIZATION

MEIOSIS

Cellular Slime Mold Life Cycle

Haploid (n)

4 cm

Diploid (2n)

Zygote

(2n)

Feeding

plasmodiumFERTILIZATION

Mature

plasmodium

(preparing to fruit)

Young

sporangium

Mature

sporangium

Stalk

MEIOSIS

Spores (n)

Germinating

spore

Amoeboid

cells (n)Flagellated

cells

(n) PlasmodialSlime MoldLife Cycle