CHAPTER 28 THE ORIGINS OF EUKAYOTIC DIVERSITY Introduction Constituents of plankton (passive drifters inwater); foundation for aquatic food chains. Free-living and parasitic forms. Eukaryotic (9+2 flagella, membranousorganelles, nuclei) Primarily unicellular (eg. Paramecium, Euglena);some colonial (Volvox) some multicellular(Seaweed) Aerobic Cilia or flagella at some time in life cycle. Sexual (syngamy- meiosis and union of gametes)and asexually reproducing. Historically Grouped into Three Categories (representing different phylogeny and nutritional modes, locomotion) Animal-like (protozoa): ingestive; chemoheterotrophs Fungus-like, absorptive; chemoheterotrophs Plant-like (algae): photosynthetic autotrophs; Chlorophyll a and accessory pigments (carotene, xanthophylls, phycobilins) Eukaryotic fossils date back 2.1 billionyears and chemical signatures ofeukaryotes date back 2.7 billion years. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Evolutionary Steps Required to be a Eukaryotic Cell
Loss of Cell Wall.Boundary must be flexible. Origin of Cytoskeleton and MTOC.Must be able tomove and divide.No good plausible theory on development. Origin of Nuclear Membrane. Appearance of digestive vesicles and membranousorganelles. Linear DNA wound around Histones. Whats So Cool About Being A Member of the Eukarya?
Eukaryotes Have MembranousOrganelles! Allows the cell tosequester/isolate materials. Separate molecules fromcytosol. Keep important processesisolated and concentrated. Specialization ofprocesses. How did these characteristics evolve?
Autogenous model of membrane development.Membraneinfolding. Endosymbiotic hypothesis (serial endosymbiosis) for originof mitochondria and chloroplasts.Cells that live within other cellsare called endosymbionts. Proposed by Lynn Margulis Aerobic heterotroph and photosynthetic prokaryotesbecome endosymbionts. Similar size Inner membrane transport proteins and enzymes similar Divide by binary fission Circular DNA without histones Transcription/translation machinery Evolution of Endomembrane System and Membrane bound organelles. Each endosymbiotic event adds a membranederived from the vacuole membrane of the hostcell that engulfed the endosymbiont. Fig. 28.5 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Phylogeny of Protista. Everything including the Kitchen Sink!
In the five-kingdom system of classification, theeukaryotes were distributed among four kingdoms:Protista, Plantae, Fungi, and Animalia. The plant, fungus, and animal kingdoms are survivingthe taxonomic remodeling so far, though theirboundaries have been expanded to include certaingroups formerly classified as protists. However, systematists have split protists into manykingdoms. Modern systematists has crumbled the former kingdomof protists beyond repair. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Protista was defined partly by structural level(mostly unicellular eukaryotes) and partly byexclusion from the definitions of plants, fungi, oranimals. However, this created a group ranging from single-celled microscopic members, simple multicellular forms, and complex giants like seaweeds. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings The kingdom Protista formed a paraphyleticgroup, with some members more closely relatedto 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 Fig. 28.8 1. Diplomonadida and Parabasala (the Archaezoa)
lack mitochondria. Ribosomes similar toprokaryotes. Trichomonas vaginalis Giardia lamblia The diplomonads have multiple flagella, twoseparate nuclei, a simply cytoskeleton, and nomitochondria or plastids. One example is Giardia lamblia, a parasite thatinfects the human intestine causing giardiasis, or"hiker's diarrhea" The most common method of acquiring Giardia is by drinking water contaminated with feces containing the parasite in a dormant cyst stage. The parabasalids include trichomonads.
Parabasalians are found only in association with animals. Some pathogenic, others commensal The best known species, Trichomonas vaginalis, inhabitsthe vagina of human females.In men this is oftensymptomless, but in women it causes painfulinflammation of the vagina (vaginitis). It can infect the vaginal lining if the normal acidity of the vaginais disturbed. Sexual transmission can spread the infection. Also, found in gut of termites and roaches digest cellulose 2. Euglenozoa: aka: Flagellates.
Several protistan groups,including the euglenoidsand kinetoplastids, useflagella for locomotion. The euglenoids(Euglenozoa) arecharacterized by ananterior pocket fromwhich one or two flagellaemerge. While Euglena is chieflyautotrophic, othereuglenoids are mixotrophicor heterotrophic. Euglena spp. Many photosynthetic with Chlorophyll a & b.
They also have a unique glucosepolymer, paramylon, as a storagemolecule. Kinetoplastids are symbiotic and include pathogenic parasites.
The kinetoplastids (Kinoplastida) have a singlelarge mitochondrion associated with a uniqueorganelle, the kinetoplast. The kinetoplast houses extranuclear DNA. Kinetoplastids are symbiotic and includepathogenic parasites. For example, Trypanosoma causes African sleeping sickness.Another human form oftrypanosomiasis occurs in the Americas and isknown as Chagas disease. African trypanosomiasis or sleeping sickness
The early phase entails bouts of fever,headaches, pains in the joints and itching. infests the central nervous system. This iswhen the characteristic signs and symptomsof the disease appear: confusion, sensorydisturbances and poor coordination,disturbance of the sleep cycle. Without treatment, the disease is fatal. If thepatient does not receive treatment before theonset of the second phase, neurologicaldamage is irreversible even after treatment. Sleeping sickness has become the first orsecond greatest cause of mortality, ahead ofHIV/AIDS, in Angola, the DemocraticRepublic of Congo and southern Sudan . 3. Alveolata: The Alveolata combines flagellatedprotists (dinoflagellates), parasites(apicomplexans), and ciliated protists (theciliates). Members of this clade have alveoli, smallmembrane-bound cavities, under the cellsurface. Their function is not known, but they may helpstabilize the cell surface and regulate water andion content. The dinoflagellates are abundant components ofthe phytoplankton that are suspended near thewater surface. Dinoflagellates and other phytoplankton form thefoundation of most marine and many freshwater foodchains. Triple membrane around the plastids.Someheterotrophic. Most dinoflagellates are unicellular, but some arecolonial. Some parasites on fish or on other protists. Each dinoflagellate specieshas a characteristic shape,often reinforced by internalplates of cellulose. Two flagella sit inperpendicular grooves in thearmor and produce aspinning movement. Blooms of dinoflagellatesproduce "red tides" whichinjure marine life. Dinoflagellate blooms, characterized by explosivepopulation (20 million per liter), cause red tides in coastalwaters. The blooms are brownish-red or pinkish-orange because of thepredominant pigments in the plastids. Toxins produced by some red-tide organisms have producedmassive invertebrate and fish kills. These toxins can be deadly to humans as well. Saxitoxin, aneurotoxin 100,000 times more potent than cocaine.Prevents Na+movement at neuromuscular junction leading to respiratory failureand cardiac arrest. Some dinoflagellates are bioluminescent.
Some dinoflagellates form mutualistic symbioseswith cnidarians, animals that build coral reefs. Photosynthetic products from the dinoflagellatesprovide the main food resource for reef communities. Some dinoflagellates are bioluminescent. An ATP-driven chemical reaction gives off light whendinoflagellates are disturbed by water movements. The function of bioluminescence may be to attractpredators that may eat the smaller predators that feedon phytoplankton. All apicomplexans are parasites of animals andsome cause serious human diseases.
The parasites disseminate as tiny infectious cells(sporozoites) with a complex of organelles specializedfor penetrating host cells and tissues at the apex of thesporozoite cell. Most apicomplexans have intricate life cycles withboth sexual and asexual stages and often require two ormore different host species for completion. Plasmodium, the parasite that causes malaria, spends partof its life in mosquitoes and part in humans. Fig The incidence of malaria was greatly diminishedin the 1960s by the use of insecticides against theAnopheles mosquitoes, which spread the disease,and by drugs that killed the parasites in humans. However, resistant varieties of the mosquitoes and thePlasmodium species have caused a malarialresurgence. About 300 million people are infected with malariain the tropics, and up to 2 million die each year. Malaria Facts Today approximately 40% of the world's populationmostly those living in the world's poorest countries is atrisk of malaria. 90% of deaths due to malaria occur in Africa south of theSahara mostly among young children. Malaria kills anAfrican child every 30 seconds. Malaria can kill by infecting and destroying red bloodcells (anaemia) and by clogging the capillaries that carryblood to the brain (cerebral malaria) or other vital organs. Malaria, together with HIV/AIDS and TB, is one of themajor public health challenges undermining developmentin the poorest countries in the world. The Ciliophora (ciliates), a diverse protist group, isnamed for their use of cilia to move and feed. Free-living, primarily solitary. Their cilia are associated with a submembranesystem of microtubules that may coordinatemovement.
Some ciliates are completely covered by rows of cilia,whereas others have cilia clustered into fewer rows ortufts. The specific arrangement of cilia adapts the ciliates fortheir diverse lifestyles. Some species have leglike structures constructedfrom many cilia bonded together, while others havetightly packed cilia that function as a locomotormembranelle. In a Paramecium, cilia along the oral groove draw in foodthat are engulfed by phagocytosis.
Like otherfreshwater protists,the hyperosmoticParameciumexpels accumu-lated water fromthe contractilevacuole. Fig c Ciliates have two types of nuclei, a largemacronucleus and usually several tiny micronuclei.
The macronucleus has 50 or more copies of the genome. The macronucleus controls the everyday functions of hecell by synthesizing RNA and is also necessary forasexual reproduction. Ciliated generally reproduce asexually by binary fissionof the macronucleus, rather than mitotic division. The micronuclei (with between 1 and 80 copies) arerequired for sexual processes that generate geneticvariation. The sexual shuffling of genes occurs duringconjugation, during which micronuclei that haveundergone meiosis are exchanged. In ciliates, sexual mechanisms of meiosis and syngamyare separate from reproduction. Fig 4. Stramenopila: aka. Chromista
The Stramenopila includes both heterotrophicand photosynthetic protists. The name of this group is derived from the presence ofnumerous fine, hairlike projections on the flagella. In most cases a hairy flagellum is paired with asmooth flagellum. almost all aquatic organisms, planktonic and sessileforms. Photosynthetic forms have chlorophyll c (unique tothis clade), brown pigment fucoxanthin. The heterotrophic stramenopiles, the oomycotes,include water molds, white rusts, and downymildews.
Some are unicellular, others have a fine network ofcoenocytic hyphae (fine, branching filaments). These hyphae have cellulose cells walls and areanalogous with the hyphae of true fungi (with chitincell walls). Unlike fungi, the diploid stage dominates inoomycotes and they have biflagellated cells. These filamentous bodies have extensive surface area,enhancing absorption of nutrients. In the Oomycota, the egg fungi, a relatively large eggcell is fertilized by a smaller sperm nucleus, forming aresistant zygote. Fig Water molds are important decomposers, mainly in fresh water.
They form cottony masses on dead algae and animals.Someparasites of fish (skin and gills) White rusts and downy mildews are parasites of terrestrialplants. They are dispersed by windblown spores. Spreads rapidly undercool and damp conditions One species of downy mildew threatened French vineyards inthe 1870s (brought from American vines) and another speciescauses late potato blight, which contributed to the Irish famine(nearly 1 mill. deaths) in the 19th century. Downy mildew on Squash Stripe Rust Include diatoms, golden algae, and brown algae.
The photosynthetic stramenopile taxa are knowncollectively as the heterokont algae. Hetero refers to the two different types of flagella. The plastids of these algae evolved by secondaryendosymbiosis. They have a three-membraneenvelope and a small amount of eukaryoticcytoplasm within the plastid. The probable ancestor was a red alga. Include diatoms, golden algae, and brown algae. The wall is divided into two parts.
Diatoms (Bacillariophyta) have unique glasslike wallscomposed of hydrated silicaembedded in an organic matrix. The wall is divided into twoparts. Diatom are abundant members of both freshwater and marine plankton.
Sexual stages are not common, but sperm may beamoeboid or flagellated, depending on species. Diatom are abundant members of both freshwaterand marine plankton. estimated that 20% -- 25% of all carbon fixation on theplanet is carried out by diatoms. Diatoms store food reserves in a glucose polymer,laminarin, and a few store food as oils. Massive accumulations of fossilized diatoms are majorconstituents of diatomaceous earth. Golden algae (Chrysophyta), named for theyellow and brown carotene and xanthophyllpigments, are typically biflagellated. Some species are mixotrophic (can becomeheterotrophic in absence of light, feeding onbacteria) and many live among freshwater andmarine plankton. While most are unicellular, some are colonial. At high densities, they can form resistant cysts thatremain viable for decades. Brown algae (Phaeophyta) are the largest and most complex algae.
are multicellular. Most species are marine. Traditionally classified as plants. Brown algae are especially common alongtemperate coasts in areas of cool water andadequate nutrients.Largest forms calledseaweeds. They owe their characteristic brown or olive colorto accessory pigments (carotenoids) in theplastids. Seaweeds inhabit the intertidal and subtidal zones of coastal waters.
Macrocystis integrifolia Bladder Kelp Egregia menziesii.Feather Boa Seaweeds inhabit the intertidal and subtidal zones of coastal waters. This environment is characterized by extreme physical conditions, including wave forces and exposure to sun and drying conditions at low tide. Seaweeds have a complex multicellularanatomy, with some differentiated tissues andorgans that resemble those in plants. These analogous features include the thallus or bodyof the seaweed. The thallus typically consists of a rootlike holdfastand a stemlike stipe, which supports leaflikephotosynthetic blades. Blade Holdfast Some brown algae have floats to raise the blades toward the surface.
Giant brown algae, known as kelps, form forests indeeper water. The stipes of these plants may be 60 m long. Many seaweeds have biochemical adaptations forintertidal and subtidal conditions.
The cells walls, composed of cellulose and gel-formingpolysaccharides (Alginic Acid, help cushion the thalliagainst agitation by waves; also help to retain water.) Many seaweeds are eaten by coastal people,including Laminaria (kombu in Japan) andPorphyra (Japanese nori) for sushi wraps. A variety of gelforming substances are extracted incommercial operations. Algin from brown algae and agar and carageenan fromred algae are used as thickeners in food, lubricants in oildrilling, or culture media in microbiology. 6. Some algae have life cycles with alternating multicellular haploid and diploid generations
The multicellular brown, red, and green algae showcomplex life cycles with alternation of multicellularhaploid and multicellular diploid forms. A similar alternation of generations evolved convergently in thelife cycle of plants. The life cycle of the brown alga Laminaria is an exampleof alternation of generations.
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. In Laminaria, the sporophyte and gametophyteare structurally different, called heteromorphic.
In other algae, the alternating generations lookalike (isomorphic), but they differ in the numberof chromosomes. 7. Rhodophyta: Red algae lack flagella
Unlike other eukaryotic algae,red algae have no flagellatedstages in their life cycle. The red coloration visible inmany members is due to theaccessory pigmentphycoerythrin. Coloration varies amongspecies and depends on thedepth which they inhabit. Unique red pigment used aschemical tags of molecules,used in research. Agars and carageenan foundin cell walls. Red algae (Rhodophyta) are the most commonseaweeds in the warm coastal waters of tropicaloceans.
Others live in freshwater, still others in soils. Some red algae inhabit deeper waters than otherphotosynthetic eukaryotes. Their photosynthetic pigments, especially phycobilins,allow some species to absorb those wavelengths (bluesand greens) that penetrate down to deep water. Reflectsred light and absorbs blue light One red algal species has been discovered offBahamas at a depth of over 260m. Most red algae aremulticellular, with somereaching a size to becalled seaweeds.
The thalli of many species are filamentous. The base of the thallus is usually differentiated into a simple holdfast. Red coralline algae depositcalcium carbonate outsideof cell wall Fig 8. Chlorophyta: the proposed ancestor of terrestrial plants.
Green algae (chlorophytes andcharophyceans) are named for their grass- green chloroplasts. These are similar in ultrastructure andpigment composition to those of plants. The common ancestor of green algae andplants probably had chloroplasts derivedfrom cyanobacteria by primaryendosymbiosis. Caulerpa Most of the 7,000 species of chlorophytes live in freshwater.
Other species are marine, inhabit damp soil or snow, or livesymbiotically within other eukaryotes. Some chlorophytes live symbiotically with fungi to form lichens, amutualistic collective. Chlorophytes range in complexity, including: biflagellated unicells that resemble gametes and zoospores colonial species and filamentous forms multicellular forms large enough to qualify asseaweeds. Spirogyra Large size and complexity in chlorophytes has evolved bythree different mechanisms:
(1) formation of colonies of individual cells (Volvox) (2) the repeated division of nuclei without cytoplasmic division to formmultinucleate filaments (Caulerpa) (3) formation of true multicellular forms by cell division and celldifferentiation (Ulva). Art imitates Life! Most green algae have both sexual and asexual reproductive stages.
Most sexual species have biflagellated gametes withcup-shaped chloroplasts. Fig 9. A diversity of protists use pseudopodia for movement and feeding
Three groups of protists use pseudopodia, cellularextensions, to move and often to feed. Most species are heterotrophs that actively hunt bacteria, otherprotists, and detritus (detritivore-feed on dead organic matter). Other species are symbiotic, including some human parasites. pinocytosis Pseudopodium emerge from anywhere in the cell surface.
Rhizopods (amoebas) are all unicellular and usepseudopodia to move and to feed. Pseudopodium emerge from anywhere in the cellsurface. To move, an amoeba extends a pseudopod, anchors itstip, and then streams more cytoplasm into thepseudopodium. Amoeboid movement isdriven by changes inmicrotubules andmicrofilaments in thecytoskeleton.
In some speciespseudopodia extend outthrough openings in aprotein shell around theorganism. Amoebas inhabit freshwater and marine environments
They may also be abundant in soils. Most species are free-living heterotrophs. Some are important parasites. These include Entamoeba histolytica which causesamoeboid dysentery in humans.Symptoms includediarrhea, abdominal pains, and potentially liver disease These organisms spread via contaminated drinkingwater, food, and eating utensils. Actinopod (heliozoans and radiolarians), rayfoot, refers to slender pseudopodia (axopodia)that radiate from the body. Each axopodium is reinforced by a bundle ofmicrotubules covered by a thin layer of cytoplasm. Most actinopods are planktonic.
The large surface area created by axopodia help them tofloat and feed. Smaller protists and other microorganisms stick to theaxopodia and are phagocytized by the thin layer ofcytoplasm. Cytoplasmic streaming carries the engulfed prey intothe main part of the cell. Most heliozoans (sun animals) live in fresh water.
Their skeletons consist of unfused siliceous (glassy) orchitinous plates. The term radiolarian refers to several groups ofmostly marine actinopods. In this group, the siliceous (SiO2)skeleton is fused intoone delicate piece. After death, these skeleton accumulate as an ooze thatmay be hundreds of meters thick in some seafloorlocations. 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 multichambered, porous shells, consisting oforganic materials hardened with calcium carbonate. Over ninety percent of the described forams are fossils.
Pseudopodia extend through the pores forswimming, shell formation, and feeding. Many forams form symbioses with algae. Over ninety percent of the described forams arefossils. The calcareous skeletons of forams are importantcomponents of marine sediments. Fossil forams are often used as chronological markersto correlate the ages of sedimentary rocks from differentparts of the world. 10. Mycetozoa: The Fungus-Like Protists
Mycetozoa (slime molds or fungusanimals) are neither fungi nor animals,but protists. Any resemblance to fungi is analogous, nothomologous, for their convergent role in thedecomposition of leaf litter and organic debris. Slime molds feed and move viapseudopodia, like amoeba, butcomparisons of protein sequences placeslime molds relatively close to the fungiand animals. The plasmodial slime molds (Myxogastrida) arebrightly pigmented, heterotrophic organisms.
The feeding stage is an amoeboid mass, theplasmodium, that may be several centimeters indiameter. The plasmodium is not multicellular, but a single mass of cytoplasm with multiple nuclei. The diploid nuclei undergo synchronous mitoticdivisions, perhaps thousands at a time.
Within the cytoplasm, cytoplasmic streamingdistributes nutrients and oxygen throughout theplasmodium. The plasmodium phagocytises food particles frommoist soil, leaf mulch, or rotting logs. If the habitat begins to dry or if food levels drop,the plasmodium differentiates into stages that leadto sexual reproduction. The cellular slime molds (Dictyostelida) straddlethe 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. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings The dominant stage in a cellular slime mold is the haploid stage.
Aggregates of amoebas form fruiting bodies thatproduce spores in asexual reproduction. Most cellular slime molds lack flagellated stages.