Chapter 28 The Origin of Eukaryotic Diversity

Chapter 28 The Origin of Eukaryotic Diversity

Figure 28.1 Unicellular and colonial eukaryotes in a drop of pond water (LM)

One trend was the evolution of multicellular prokaryotes, where cells specialized for different functions. A second trend was the evolution of complex communities of prokaryotes, with species benefiting from the metabolic specialties of others. A third trend was the compartmentalization of different functions within single cells, an evolutionary solution that contributed to the origins of eukaryotes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Under one evolutionary scenario, the endomembrane system of eukaryotes (nuclear envelope, endoplasmic reticulum, Golgi apparatus, and related structures) may have evolved from infoldings of plasma membrane. Another process, called endosymbiosis, probably led to mitochondria, plastids, and perhaps other eukaryotic features. Fig. 28.4

2. Mitochondria and plastids evolved from endosymbiotic bacteria
The evidence is now overwhelming that the eukaryotic cell originated from a symbiotic coalition of multiple prokaryotic ancestors. A mechanism for this was originated by a Russian biologist C. Mereschkovsky and developed extensively by Lynn Margulis of the University of Massachusetts.

Other organelles: cilia, flagella, basal bodies and centrioles.
The theory of serial endosymbiosis proposes that mitochondria and chloroplasts were formerly small prokaryotes living within larger cells. Cells that live within other cells are called endosymbionts. The proposed ancestors of mitochondria were aerobic heterotrophic prokaryotes. The proposed ancestors of chloroplasts were photosynthetic prokaryotes. Other organelles: cilia, flagella, basal bodies and centrioles. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Several lines of evidence support a close similarity between bacteria and the chloroplasts and mitochondria of eukaryotes. These organelles and bacteria are similar is size. Enzymes and transport systems in the inner membranes of chloroplasts and mitochondria resemble those in the plasma membrane of modern prokaryotes. Replication by mitochondria and chloroplasts resembles binary fission in bacteria. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The single circular DNA in chloroplasts and mitochondria lack histones and other proteins, as in most prokaryotes. Both organelles have transfer RNAs, ribosomes, and other molecules for transcription of their DNA and translation of mRNA into proteins. The ribosomes of both chloroplasts and mitochondria are more similar to those of prokaryotes than to those in the eukaryotic cytoplasm that translate nuclear genes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A comprehensive theory for the origin of the eukaryotic cell must also account for the evolution of the cytoskeleton and the microtubule apparatus of the eukaryotic cilia and flagella. Some researchers have proposed that cilia and flagella evolved from symbiotic bacteria (especially spirochetes). However, the evidence for this proposal is weak. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

A Spirochete living symbiotically with a protist may have evolved into the organelles flagella and cilia

3. The eukaryotic cell is a chimera of prokaryotic ancestors
The chimera of Greek mythology was part goat, part lion, and part serpent. Similarly, the eukaryotic cell is a chimera of prokaryotic parts: mitochondria from one bacteria plastids from another nuclear genome from the host cell (the prokayotic symbiont passes some of its genetic control to the host’s nucleus- thus losing its independence) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Example of cell with symbiotic bacteria

4. Secondary endosymbiosis increased the diversity of algae
Taxonomic groups with plastids are scattered throughout the phylogenetic tree of eukaryotes. These plastids vary in ultrastructure. The chloroplasts of plants and green algae have two membranes. The plastids of others have three or four membranes. These include the plastids of Euglena (with three membranes) that are most closely related to heterotrophic species.

The best current explanation for this diversity of plastids is that plastids were acquired independently several times during the early evolution of eukaryotes. Those algal groups with more than two membranes were acquired by secondary endosymbiosis. It was by primary endosymbiosis that certain eukaryotes first acquired the ancestors of plastids by engulfing cyanobacteria. Secondary endosymbiosis occurred when a heterotrophic protist engulfed an algae containing plastids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Formation of Chloroplast
cyanobacteria green algae green plants

Each endosymbiotic event adds a membrane derived from the vacuole membrane of the host cell that engulfed the endosymbiont. 3 2 Fig. 28.5

Figure 28.3 Diversity of plastids produced by secondary endosymbiosis
Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Red algae Green algae Secondary Plastid Dinoflagellates Apicomplexans Ciliates Stramenopiles Euglenids Chlorarachniophytes Alveolates Green Plants 2 3

Horizontal Gene Transfer
Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring Genes from endosymbiotic bacteria may have undergone HGT to its host chromosomes eg. genes for ATP synthase.

5. The origin of eukaryotes catalyzed a second great wave of diversification
The first great adaptive radiation, the metabolic diversification of the prokaryotes, set the stage for the second. The second wave of diversification was catalyzed by the greater structural diversity of the eukaryotic cell. The third wave of diversification followed the origin of multicellular bodies in several eukaryotic lineages.

The kingdom Protista formed a paraphyletic group, with some members more closely related to animals, plants, or fungi than to other protists. Systematists have split the former kingdom Protista into as many as 20 separate kingdoms. Still,“protist” is used as an informal term for this great diversity of eukaryotic kingdoms. Fig. 28.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

polyphyletic monophyletic

Plasmodial slime molds
Diplomonads Parabasalids Kinetoplastids Euglenids Dinoflagellates Apicomplexans Ciliates Oomycetes Diatoms Golden algae Brown algae Chlorarachniophytes Foraminiferans Radiolarians Gymnamoebas Entamoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Metazoans Red algae Chlorophytes Charophyceans Plants Ancestral eukaryote Chlorophyta Plantae Rhodophyta Animalia (Opisthokonta) (Viridiplantae) Diplomonadida Parabasala Euglenozoa Alveolata Stramenopila Cercozoa Radiolaria Amoebozoa Flagella (>2), 2 nuclei, no mitochondria, no plastids, simple cytoskeleton, EX: Giardia

Figure 28.5 Diplomonads and parabasalids
(a) Giardia intestinalis, a diplomonad (colorized SEM) Flagella Undulating membrane 5 µm (b) Trichomonas vaginalis, a parabasalid (colorized SEM)

Diplomonads Parabasalids Kinetoplastids Euglenids Dinoflagellates Apicomplexans Ciliates Oomycetes Diatoms Golden algae Brown algae Chlorarachniophytes Foraminiferans Radiolarians Gymnamoebas Entamoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Metazoans Red algae Chlorophytes Charophyceans Plants Ancestral eukaryote Chlorophyta Plantae Rhodophyta Animalia (Opisthokonta) (Viridiplantae) Diplomonadida Parabasala Euglenozoa Alveolata Stramenopila Cercozoa Radiolaria Amoebozoa Anterior pocket where 1-2 flagella emerge, paramylum, a glucose polymer used for storage, many are autotrophic or heterotrophic

Figure 28.7 Trypanosoma, the kinetoplastid that causes sleeping sickness
Trypanosoma is a kinetoplastid from the Kingdom Euglenozoa it is the cause of African sleeping sickness which is spread by the bite of the Tsetse fly Kinetoplast- an organelle that houses extracellular DNA w/ associated mitochondria 9 m

Trypanosoma is a kinetoplastid from the Kingdom Euglenozoa
it is the cause of African sleeping sickness which is spread by the bite of the Tsetse fly Kinetoplast- an organelle that houses extracellular DNA w/ associated mitochondria

Figure 28.8 Euglena, a euglenid commonly found in pond water
Long flagellum Short flagellum Nucleus Plasma membrane Paramylon granule Chloroplast Contractile vacuole Light detector: swelling near the base of the long flagellum; detects light that is not blocked by the eyespot; as a result, Euglena moves toward light of appropriate intensity, an important adaptation that enhances photosynthesis Eyespot: pigmented organelle that functions as a light shield, allowing light from only a certain direction to strike the light detector Pellicle: protein bands beneath the plasma membrane that provide strength and flexibility (Euglena lacks a cell wall) Euglena (LM) 5 µm Anterior pocket where 1-2 flagella emerge, paramylum, a glucose polymer used for storage, many are autotrophic or heterotrophic

Euglena – Kingdom Euglenozoa
Anterior pocket where 1-2 flagella emerge, paramylum, a glucose polymer used for storage, many are autotrophic or heterotrophic Paramylum-glucose polymer This Kingdom has changed classification several times because it is unicellular, photosynthetic and heterotrophic MIXOTROPH

Diplomonads Parabasalids Kinetoplastids Euglenids Dinoflagellates Apicomplexans Ciliates Oomycetes Diatoms Golden algae Brown algae Chlorarachniophytes Foraminiferans Radiolarians Gymnamoebas Entamoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Metazoans Red algae Chlorophytes Charophyceans Plants Ancestral eukaryote Chlorophyta Plantae Rhodophyta Animalia (Opisthokonta) (Viridiplantae) Diplomonadida Parabasala Euglenozoa Alveolata Stramenopila Cercozoa Radiolaria Amoebozoa

Figure 28.9 Alveoli Flagellum Alveoli 0.2 µm

Ceratium is a dinoflagellate from the Kingdom Aveolota

Figure 28.10 Pfiesteria shumwayae, a dinoflagellate

Pfiesteria piscicida is another dinoflagellate that can produce toxins that can result in red tides -Caretenoids pigments give it its characteristic color Their characteristic shape is reinforced by internal plates of cellulose – they have chloroplasts they have two unequal flagella set in perpendicular grooves which result in its characteristic spinning motion

28.17 Dino Flagellate

Some dinoflagellates act as mutualistic symbionts in corals

Figure 28.12 Structure and Function in the Ciliate Paramecium caudatum
Thousands of cilia cover the surface of Paramecium. The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore. Paramecium, like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis. Oral groove Cell mouth Micronucleus Macronucleus FEEDING, WASTE REMOVAL, AND WATER BALANCE Contractile vacuole

CONJUGATION AND REPRODUCTION
3 Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells. 9 The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. 8 Three rounds of mitosis without cytokinesis produce eight micronuclei. 7 Micronuclei fuse, forming a diploid micronucleus. 6 The cells separate. 5 The cells swap one micronucleus. 4 Three micronuclei in each cell disintegrate. The remaining micronucleus in each cell divides by mitosis. Meiosis of micronuclei produces four haploid micronuclei in each cell. 2 Two cells of compatible mating strains align side by side and partially fuse. 1 MICRONUCLEAR FUSION Diploid micronucleus Haploid micronucleus MEIOSIS Compatible mates Key Conjugtion Reproduction Macronucleus

Just the micronucleus undergo meiosis and syngamy which increases genetic diversity

The cilia on a paramecium

28.12 Paramecium Vacuole

Stentor is a ciliate under the Kingdom Aveolata
Solitary freshwater cells Two types of nuclei -macronucleus and several micronuclei has two or more copies of the genome packaged in small units containing hundreds of copies of just a few genes Ciliates are the most complex within the Kingdom of Aveolata

Stylonychia is another ciliate

All apicomplexans are parasites of animals and some cause serious human diseases.
The parasites disseminate as tiny infectious cells (sporozoites) with a complex of organelles specialized for penetrating host cells and tissues at the apex of the sporozoite cell. Most apicomplexans have intricate life cycles with both sexual and asexual stages and often require two or more different host species for completion. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The apical complex is its characteristic structure

Figure 28.11 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria
Inside mosquito Inside human Sporozoites (n) Oocyst MEIOSIS Liver Liver cell Merozoite Red blood cells Gametocytes FERTILIZATION Gametes Zygote (2n) Key Haploid (n) Diploid (2n) cell Apex 0.5 µm An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva. The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells (see TEM below). The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect new red blood cells. Some merozoites form gametocytes. Gametes form from gametocytes. Fertilization occurs in the mosquito’s digestive tract, and a zygote forms. The zygote is the only diploid stage in the life cycle. Another Anopheles mosquito bites the infected person and picks up Plasmodium gametocytes along with blood. An oocyst develops from the zygote in the wall of the mosquito’s gut. The oocyst releases thousands of sporozoites, which migrate to the mosquito’s salivary gland. 1 2 3 4 5 6 7

28.12 Vorticella Habitat

Stramenopila Water Molds and their relatives (Oomycota) Diatoms
lack chloroplasts unicellular or have coenocytic hyphae cause of the Irish potato famine Diatoms Golden Algae have yellow and brown carotenoid and xanthophyll accessory pigments Brown Algae

Stramenopila Chloroplasts of stramenopiles have two additional membranes outside of the usual chloroplast This is evidence that the chloroplasts did not evolve directly from cyanobacteria - it probably came from a eukaryotic source - probably and endosymbiotic red algae

Figure 28.13 Stramenopile flagella
Smooth flagellum Hairy 5 µm

Figure 28.14 The life cycle of a water mold (layer 1)
MEIOSIS Egg nucleus (n) Key Haploid (n) Diploid (2n) Oogonium Antheridial hypha with sperm nuclei (n) Oomycetes causes molds, mildew, rusts, blights

Zoosporangium (2n) Zygote germination FERTILIZATION SEXUAL REPRODUCTION Zygotes (oospores) Key MEIOSIS Egg nucleus (n) Antheridial hypha with sperm nuclei Haploid (n) Diploid (2n) Oogonium Cell walls made of cellulose, dominant diploid causes potato late blight (Irish famine)

Cyst Zoospore (2n) ASEXUAL REPRODUCTION Zoosporangium Germ tube Zygote germination FERTILIZATION SEXUAL Zygotes (oospores) Key MEIOSIS Egg nucleus (n) Haploid (n) Diploid (2n) Oogonium Figure The life cycle of a water mold (layer 3) Antheridial hypha with sperm nuclei (n)

28.14 Water Mold Oogonium Cell walls of cellulose, dominant diploid causes potato blight (Irish famine)

Diatoms (Bacillariophyta) have unique glasslike walls composed of hydrated silica embedded in an organic matrix. Autotrophic The wall is divided into two parts that overlap like a shoe box and lid. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The glass like shell of a diatom (bacillariophyta)

Fossilized diatoms make up the majority of diatomaceous earth

28.16 Diatoms Moving

Brown algae (Phaeophyta) are the largest and most complex algae.
Most brown algae are multicellular. Most species are marine. Brown algae are especially common along temperate coasts in areas of cool water and adequate nutrients. They owe their characteristic brown or olive color to accessory pigments like fucoxanthin in the plastids. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The thallus typically consists of a leaflike photosynthetic blades supported by a stemlike stipe, and a rootlike holdfast. The brown accessory pigments mask the chlorophyll in brown algae

Fucus a brown algae

Giant kelp

Figure 28.18 Seaweeds: adapted to life at the ocean’s margins
Blade Stipe Holdfast

Figure A kelp forest

Figure 28.20 Edible seaweed (a) The seaweed is grown on nets in
shallow coastal waters. (b) A worker spreads the harvested seaweed on bamboo screens to dry. (c) Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.

The sequoia of the sea, a giant bladder kelp (Macrocystic pyrifera) floats with the current in California's Monterey Bay. Reaching 200 feet (61 meters) in length, the plant serves double duty: It provides habitat and nourishment for marine life and is a source of algin, a stabilizing, thickening, gelling, and suspending agent used in human food preparation.

The life cycle of the brown alga Laminaria is an example of alternation of generations.
heteromorphic The diploid individual, the sporophyte, produces haploid spores (zoospores) by meiosis. The haploid individual, the gametophyte, produces gametes by mitosis that fuse to form a diploid zygote. Fig

Diplomonads Parabasalids Kinetoplastids Euglenids Dinoflagellates Apicomplexans Ciliates Oomycetes Diatoms Golden algae Brown algae Chlorarachniophytes Foraminiferans Radiolarians Gymnamoebas Entamoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Metazoans Red algae Chlorophytes Charophyceans Plants Ancestral eukaryote Chlorophyta Plantae Rhodophyta Animalia (Opisthokonta) (Viridiplantae) Diplomonadida Parabasala Euglenozoa Alveolata Stramenopila Cercozoa Radiolaria Amoebozoa Dazzling performers enjoy a strong, creative repertoire at rehearsal concerts

Pseudopodium emerge from anywhere in the cell surface.
Cercozoans (amoebas) are all unicellular and use pseudopodia to move and to feed. Pseudopodium emerge from anywhere in the cell surface. To move, an amoeba extends a pseudopod, anchors its tip, and then streams more cytoplasm into the pseudopodium. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Chlorarachniophytes Normally they have the form of small amoebae, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net.

Foraminiferans, or forams, are almost all marine.
Most live in sand or attach to rocks or algae. Some are abundant in the plankton. Forams have snail-like, coiled, multichambered, porous shells, consisting of organic materials hardened with calcium carbonate. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Foraminiferans - pore bearing shells
many have symbiotic algae in which they derive benefit from photosynthesis Foram fossil are excellent markers for dating marine sediment and sedimentary rock

Radiolarians have skeletons made of silica
most of the marine ooze found on the ocean floor is composed of their skeletons

Actinopod (heliozoans and radiolarians), “ray foot,” refers to slender pseudopodia (axopodia) that radiate from the body. Each axopodium is reinforced by a bundle of microtubules covered by a thin layer of cytoplasm. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 28.4 A tentative phylogeny of eukaryotes

Amoebozoans Lobe shaped rather than thread like pseudopodia
the microtubules and microfilaments of the cytoskeleton help in amoeboid movement VIDEO

Slime molds (mycetozoans) have structural adaptations and life cycles that enhance their ecological roles as decomposers Mycetozoa (slime molds or “fungus animals”) are neither fungi nor animals, but protists. Any resemblance to fungi is analogous, not homologous, for their convergent role in the decomposition of leaf litter and organic debris. Slime molds feed and move via pseudopodia, like amoeba, but comparisons of protein sequences place slime molds relatively close to the fungi and animals.

The plasmodial slime molds (Myxogastrida) are brightly pigmented, heterotrophic organisms.
The feeding stage is an amoeboid mass, the plasmodium, that may be several centimeters in diameter. The plasmodium is not multicellular, but a single mass of cytoplasm with multiple nuclei. Fig

Plasmodial Slime Mold belongs to Mycetozoa/ Myxogastrida
is composed of ONE multinucleated cell or amoeboid mass called a plasmodium most species are diploid

The cellular slime molds (Dictyostelida) straddle the line between individuality and multicellularity. The feeding stage consists of solitary cells. When food is scarce, the cells form an aggregate (“slug”) that functions as a unit. Each cell retains its identity in the aggregate. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Cellular Slime Molds are multicellular
haploid have fruiting bodies

Besides chlorophyll a, red algae has an accessory pigment phycoerythin that give it its red color by masking the chlorphyll They are multicellular and live in deep water

Figure 28.28 Red algae (b) Dulse (Palmaria palmata). This edible
Bonnemaisonia hamifera. This red alga has a filamentous form. (a) Dulse (Palmaria palmata). This edible species has a “leafy” form. (b) A coralline alga. The cell walls of coralline algae are hardened by calcium carbonate. Some coralline algae are members of the biological communities around coral reefs. (c)

The plastids of red algae evolved from cyanobacteria by primary endosymbiosis

Figure 28.30 Colonial and multicellular chlorophytes
Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM). (a) Caulerpa, an inter- tidal chlorophyte. The branched fila- ments lack cross-walls and thus are multi- nucleate. In effect, the thallus is one huge “supercell.” (b) Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides. (c) 20 µm 50 µm

Volvox is a colonial Green Alga
-most are unicellular -closely related to plants Chlorophyta Green Algae are photosynthetic autotrophs that arose by an endosymbiotic association between a flagellated, heterotrophic eukaryote and a cyanobacterium

28.30 Volvox Colony

28.30 Volvox Flagella

In spirogyra there is one or more large spiral chloroplast
Sexual reproduction occurs between conjugation tubules.

Most green algae have both sexual and asexual reproductive stages.
Most sexual species have biflagellated gametes with cup-shaped chloroplasts. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Life cycle of Chlamydomonas
Isogamy gametes of equal size Ansiogamy when the male and female gametes are different in size or shape

Photosynthetic protists have evolved in several clades that also have heterotrophic members.
Different episodes of secondary endosymbiosis account for the diversity of protists with plastids. Fig Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Ulva is a multicellular green alga with specialized cells that organized into tissues

Isomorphic alternation of generations in Ulva

The choanoflagellate is a colonial protist that is believed to be the ancestor of animals

Chapter 28 The Origin of Eukaryotic Diversity

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