of Principles Eukaryotic Diversity
Eukaryotic Diversity II
1. Friday Endosymbiosis HW due
2. Friday - GAE involves a computer
simulation of diffusion
3. One laptop per group of 3 or two
laptops per group of 4 or 5 with
downloaded app. Wolfram CDF Player,
plus diffusion simulation from course
website. Enable dynamic button
4. Fully charged laptop, watch/timer,
calculator
C & R 28.1
C & R 28.1
Independent origins of eukaryotic multicellularity > 20 origins
Basal
Photosynthetic
Heterotrophic
Eukaryotes evolved as complex assemblages of several
organisms
Endosymbiosis the uptake of another organism and its
evolution into an organelle. (Focus of Fridays discussion)
Eukaryotes acquired aerobic respiration and oxygenic
photosynthesis from bacterial endosymbionts.
Prokaryotes lateral gene transfer
Eukaryotes endosymbiosis (with internal LGT)
Unifying features include: nucleus, sexual life cycle,
endomembrane system, and complex cytoskeleton.
Eukaryotes originated the sexual stages, i.e., syngamy
and meiosis, in life cycles.
Eukaryotes manifest more organellar, cellular, and
multicellular diversity than prokaryotes.
Eukaryotes can be divided into three artificial groups:
basal, heterotrophic and photosynthetic groups.
Group discussion - Why are unicellular organisms
constrained in their ability to develop large sizes?
Thiomargarita
Likely origin of
multicellularity in
some lineages
unicellular flagellate
Valonia
Thiomargarita - the largest known unicellular prokaryote (0.75 mm in
diameter). It grows buried in sulfide-rich ocean sediments.
Valonia - a very large unicellular eukaryote (5 cm in diameter) in the
green algae. It grows in protective sites on coral reefs.
Basal flagellated eukaryotes
1
Group discussion - Why are unicellular organisms
constrained in their ability to develop large sizes?
What are the convergent design strategies operating in
the evolution of multicellular eukaryotes?
Colony - a loose association of independent cells
F. Fig. 28-13
Thiomargarita
Valonia
Chlamydomonas (unicellular)
Gonium (small colony)
Pandorina (large colony)
Volvox (multicellular?)
Volvox - up to 60,000 Chlamydomonas-like cells
limited cell specialization but some organization
specialized cells are capable of regenerating the organism
cells can not live as independent unicells
Design strategies of multicellular eukaryotes
Choanoflagellates and sponges
Colony - a loose association of independent cells
Choanoflagellates
Sponges
Choanoflagellates - closest living relatives of the animal lineage
adult cells as individual cells or a colony attached to substrate
phagocytosis of prokaryotes and food particles
individual cells undergo asexual reproduction
Sponges - multicellular sessile animals composed of several cell types
totipotency - an individual cell can often regenerate the entire organism
separated cells can reform the sponge
F. Fig. 31.11
Feeding cells (or choanocytes) of sponges are virtually identical
to choanoflagellates
2
Design strategies of large eukaryotes
2. Acellularity - repeated mitosis w/o intervening cell division
Caulerpa taxifolia (also known as the killer alga)
human-modified invasive species
causing ecological devastation in new
environments
over 10,000 acres of Mediterranean
Sea have become a toxic green desert
discovered at seaports all over the
world
Green alga Caulerpa
Plasmodial slime mold Physarum
www.physicspost.com/science-article-124.html
Key process - very rapid cytoplasmic streaming
Support - internal structs (C) or flat web-like form (P)
Cell division for sexual reproduction and wound healing
Design strategies of multicellular eukaryotes
3. Multicellularity - tight association of many cells carrying out
specialized vegetative and reproductive functions
Multicellular photosynthetic organisms
Red alga
Plocamium
Fig. 31.11A
Independent evolution ---> unique molecular mechanisms for each lineage
Several convergent designs of multicellular organisms related to their nutrition:
1. Multicellular photosynthetic organisms convergent designs of flat leaves,
tubular stems and attaching roots/holdfasts/etc.
2. Absorptive organisms - dispersed unicellular vegetative stages, then
aggregated reproductive stages - e.g., cellular slime molds and fungi.
3. Ingestive organisms (animals) nervous, muscular, and digestive systems
Brown alga
Postelsia
Green alga
Ulva
Fig. 31.11A
Flowering plant
Tomato
Convergent design - flat leaves, tubular stems and
attaching roots/holdfasts.
3
Some absorptive organisms have unicellular or filamentous
vegetative stages and multicellular reproductive stages
F Fig. 30.6
Fig. 28.30
Cellular slime mold Dictyostelium
Typical club fungi
Learning Objectives: Design constraints on multicellular
eukaryotes (more later)
Major physiochemical constraints on large organisms diffusion, scaling, and
mechanical support
Multicellular form and function diffusion controls transport and signaling
processes at membrane and cellular levels vs. other mechanisms operate for
long-distance activities.
Multicellular organisms often develop generalized cells for housekeeping
activities, and specialized cells for particular functions, such as reproduction
Different lineages evolved analogous biological solutions to the challenges of
large size.
This design strategy - maximizes surface area and cellular distribution for
nutrient uptake during vegetative growth
- enhances aerial dispersal of asexual spores
Fig. 31.11B
Fig. 31.11A
Principles of Eukaryotic Diversity
C & R 28.1
Eukaryotes evolved as complex assemblages of several
organisms
Endosymbiosis the uptake of another organism and its
evolution into an organelle. (Focus of Fridays discussion)
Eukaryotes acquired aerobic respiration and oxygenic
photosynthesis from bacterial endosymbionts.
Prokaryotes lateral gene transfer
Eukaryotes endosymbiosis (with internal LGT)
Unifying features include: nucleus, sexual life cycle,
endomembrane system, and complex cytoskeleton.
Eukaryotes originated the sexual stages, i.e., syngamy
and meiosis, in life cycles.
Eukaryotes manifest more cellular, organellar, and
multicellular diversity than prokaryotes.
Eukaryotes can be divided into three artificial groups:
basal, heterotrophic and photosynthetic groups.
Traditional hypothesis of eukaryote phylogeny
Absorption
Fungi
Molds
Photosynthesis
Ingestion
Algae Plants Protozoa Animals
Ancestral eukaryote
Molds - absorptive, fungus-like protists
Algae - photosynthetic, plant-like protists
Protozoa - ingestive, animal-like protists
4
Protist diversity: Poor coupling between
protist phylogeny and nutritional strategy
Euglena species
photosynthetic
heterotrophic
mixotrophs
See F. Fig. 29.26
C & R 28.3
Some lineages acquired,
then lost plastids
Euglena
An evolutionary survey of protist diversity
Eukaryote Diversity (In Brief)
Three Groups for us - Freeman Fig. 29.8
1
1) Basal groups - excavates
2) Heterotrophic groups
3) Photosynthetic groups
3
2
Protists - paraphyletic group
all eukaryotes except plants,
fungi, and animals
How did this organism make ATP?
Incredible diversity in each major eukaryotic lineage
Several nutritional strategies in most lineages
Prokaryotic cells great metabolic flexibility
Eukaryotic cells great structural flexibility
Multicellularity - repeated evolution and different modes
Protists play important roles in the environment and as
pathogens
5
What if I told you ?
Questions
No mitochondria in Excavates
No M
M
M
M
M
M
M
M
What does this imply about:
1) How the excavates make ATP?
2) The evolution of mitochondria?
Two hypotheses for the origin
of mitochondria
1) Late origin - Excavates as basal
eukaryotes that split off before the
evolution of mitochondria
2) Early origin, loss in excavates
What evidence could distinguish these
two hypotheses?
Evidence
Excavates have
Mitochondrial genes in nuclear genome
Mitochondrial relics hydrogenosomes (H2
generating organelles) - double membrane-bound
organelles with some mitochondrial reactions but
no ETC
Implications
Single origin of mitochondria
2 loss in Excavates
And in a number of other groups
Predict what these groups have in common
6
1) Excavates
2)Heterotrophic lineages -
Anaerobes no surprise
Hydrogenosomes vestigial mitochondria
Diplomonads (e.g. Giardia)
Usually commensals in animal guts
Some parasites campers diarrhea from
drinking stagnant water
Parabasalids animal symbionts/parasites
Trichonympha in termite guts - cellulose digestion
Close relationship of fungi
and animals more later
Choanoflagellates - sister
group to animals; unicellular/
colonial forms more later
Feeding current via beating
flagella
with bacterial endosymbionts making cellulase;
other bacterial ectosymbionts (spirochaetes) insert into
the collar to make the protist mobile
Trichomonas vaginalis
Trich - common venereal disease
2) Heterotrophic lineages -
3) Photosynthetic lineages
Amoebozoa phagocytosis or absorption;
amoeboid movement one stage or whole life
Other protists (and human macrophages)
AM, too
plasmodial slime mold
lobose amoeba
Three main groups alveolates, stramenopiles, and plants
The plastid endosymbiosis story?
7
3) Alveolates
Dinoflagellates
Unicellular protists including flagellated protists (dinoflagellates),
parasites (apicomplexans), and ciliated protists (ciliates).
Alveoli are small membrane-bound cavities under the cell
surface with unknown function.
Related organisms with great morphological
diversity
dinoflagellate
apicomplexan
Very abundant component of marine phytoplankton
many are photosynthetic
Internal armor of cellulose plates with two perpendicular
grooves with flagella.
Most common species of symbiotic zooxanthellae in
corals - primary producers of coral reefs
Dinoflagellate blooms cause red tides, sometimes
resulting
resulting in paralytic shellfish poisoning
ciliate
www.ucmp.berkeley.edu/
www.mbari.org
www.botany.hawaii.edu
Apicomplexans - all animal parasites
Dinoflagellates red tide
C & R Fig. 28.13
Plasmodium life cycle
Plasmodium infection in
red blood cells
Intricate life cycles with several hosts - very evasive
Apical complex of microtubules for penetrating host cell
Most familiar example - Plasmodium causes malaria
Complete sequencing of all genomes involved in malaria - human,
mosquito, and Plasmodium
Eukaryotic pathogens are tough for us to deal with! Why?
Vestigial plastid from ancient 2 endosymbiosis
8
Ciliates
C & R 28.14
F Fig. 28.12
Diverse protist group unified by
their use of cilia for feeding and
movement.
Microtubules underlying outer
membrane act to coordinate
ciliary beating.
Large macronucleus (>50 total
genomes) for RNA synthesis
and asexual binary fission.
Tiny micronuclei for exchange
during sexual conjugation.
3) Stramenopiles
www.unikassel.de
oomycetes
Diverse unicellular and multicellular protists
Heterotrophic group - oomycetes
(water molds and downy mildews)
Photosynthetic group - heterokont
algae (diatoms and brown algae)
Stramenopile refers to hair-like
Stramenopile
projections on their flagella that
projections
are usually restricted to motile
are
reproductive cells
reproductive
F Fig. 29.2
flagellum
diatoms
F Fig. 29.7
F Fig. 28.15
Oomycetes - water molds and relatives
Often multi-nucleate branched hyphae
Major decomposers in aquatic habitats
Convergent body plan and nutritional
strategy with the fungi
Heterokont algae
All groups have brown plastids resulting from
2 and 3 endosymbiosis
Amazing structural diversity
C & R 28.16
Devastating plant pathogens
For example, Phytophthora infestans
causes potato late blight that led to
the Irish famines in mid 1800s.
P. ranorum causes a new disease
known as sudden oak death in
California.
C & R Fig. 28.17
C & R Fig. 28.19
F Fig. 29.32
F Fig. 29.34
Diatoms - the grass of the seas
Kelps - the trees of the seas
agronomy.ucdavis.edu
9
3) Plants- All lineages with 1 endosymbiosis
Red algae
Red plastids - same basic antenna pigments as
cyanobacteria
Very complex life cycles
Largest algae of warm tropical waters
Uniaxial and multiaxial filament construction
10