Chapter 29
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Chapter 29 Protists 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eukaryotic Origins • Eukaryotic cells differ from prokaryotes – Presence of a cytoskeleton – Compartmentalization (nucleus and organelles) • Appearance of eukaryotes in microfossils occurred about 1.5 BYA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 50 µm © Andrew H. Knoll/Harvard University 2 • Endosymbiosis supported by – DNA inside mitochondria and chloroplasts • DNA similar to bacteria DNA in size and character – Ribosomes inside mitochondria similar to bacterial ribosomes – Chloroplasts and mitochondria replicate by binary fission – not mitosis • Mitosis evolved in eukaryotes 6 Defining Protists • Most diverse of the four eukaryotic kingdoms • United on the basis that they are not fungi, plants, or animals • Vary considerably in every other aspect – Unicellular, colonial, and multicellular groups – Most are microscopic but some are huge – All symmetries – All types of nutrition 7 • Protista is not monophyletic – Paraphyletic – Does not represent any evolutionary relationships • Grouping 15 major protist phyla into 7 monophyletic groups – 60 lineages are still not placed 8 • Cell surface – Plasma membrane – Extracellular material (ECM) in some • Diatoms – Silica shells • Cysts – Dormant cell with resistant outer covering – Used for disease transmission 10 • Locomotion – Flagella • One or more – Cilia • Shorter and more numerous than flagella – Pseudopodia (“false feet”) • Lobopods – large, blunt • Filopods – thin, branching • Axopods – thin, long 11 • Nutrition – Phototrophs – Heterotrophs • Phagotrophs – Ingest particulate food matter • Osmotrophs – Soluble food matter – Mixotrophs are both phototrophic and heterotrophic 12 • Asexual reproduction – Typical mode of reproduction – Some species have an unusual mitosis • Mitosis – equal size daughter cells • Budding – one daughter cell smaller • Schizogony – cell division preceded by several nuclear divisions; produces several individuals • Sexual reproduction – May be obligate, or only under stress – Meiosis is a major eukaryote innovation – Union of haploid gametes which are produced by meiosis – Advantage in allowing frequent genetic recombination 13 • Protists are bridge to multicellularity – From single cells to colonies to true multicellularity – Arisen multiple times – Fosters specialization – Few innovations have had as great an influence on the history of life 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rhizaria Chromalveolata Opisthokonta • They share similarities in cytoskeletal features and DNA sequences 15 Animals Fungi Choanoflagellida • This group consists of diplomonads, parabasalids, and euglenozoans Amoebozoa Euglenozoa Parabasalids Land plants Diplomonads Charophytes Chlorophytes Cercozoa Rhodophyta Radiolara Foraminifera Diatoms Brown algae Ciliates Amoeboza Stramenopila Oomycetes Dinoflagellates Apicomplexans EXCAVATA Alveolata Archaeplastida Excavata Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diplomonads • • • • • Unicellular Move with flagella 2 nuclei 0.6 µm Giardia Degenerate mitochondria • Mitochondrial genes found in nucleus © Science VU/E. White/Visuals Unlimited 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parabasalids • Live in termite guts 0.8 µm © Science VU/E. White/Visuals Unlimited – Host cellulose degrading bacteria • • • • Trichomonas vaginalis – STD Undulating membrane for locomotion Use flagella Lack mitochondria – derived trait 17 Euglenozoa Euglenids and Kinetoplastids • Among the earliest eukaryotes to possess mitochondria • 1/3rd have chloroplasts and are autotrophic – May become heterotrophic in the dark • Others lack chloroplasts and are heterotrophic • No sexual reproduction 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Euglena – Two anterior (and unequal) flagella a. 6.5 µm © Andrew Syred/Photo Researchers, Inc. • Attached at reservoir – Contractile vacuoles – collect excess water – Stigma – movement towards light – Numerous small chloroplasts • From ingestion of green algae – Concept of a single Euglena genus is now being debated 19 • Kinetoplastids – 2nd major group in Euglenozoa – Unique, single mitochondrion • DNA maxicircles and minicircles – Trypanosomes cause human diseases • African sleeping sickness – tsetse fly • Leishmaniasis – sand fly • Chagas disease – skin contact with urine or blood of infected wild animal 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood cell Trypanosome a. 20 µm b. a: © KAGE-Mikrofotografie; b: © Edward S. Ross • Difficult to control because organisms repeatedly change their protective coat • Methods: – Release of sterilized flies – Traps that are scented like cows but treated with insecticides – Sequencing of genomes revealed core of common genes in all 3 – hope for single drug target 22 CHROMALVEOLATES Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amoeboza Opisthokonta • They may have arisen by one or more secondary endosymbiotic events 23 Animals Choanoflagellida Fungi Amoebozoa Euglenozoa Parabasalids Land plants Diplomonads Charophytes Chlorophytes Cercozoa Rhodophyta Radiolara Foraminifera Brown algae Diatoms Ciliates Archaeplastida Excavata Stramenopila Oomycetes Dinoflagellates Alveolata Apicomplexans • This is a supergroup consisting of two branches: the alveolates and the stramenopila Chromalveolata Rhizaria Alveolata Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Flattened vesicles called alveoli • Includes: – Dinoflagellates – Apicomplexans – Ciliates Alveolar sac Apical complex 1 µm © Vern Carruthers, David Elliott • Common lineage despite diverse modes of locomotion 24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ptychodiscus Dinoflagellates Noctiluca Gonyaulax Ceratium • • • • Photosynthetic, unicellular with flagella Live in aquatic environments Some are luminescent Do not appear to be directly related to any other phylum • “Red tide” are “blooms” – fish, birds, and marine mammals may die from toxins • DNA not complexed with histones 25 Apicomplexans • Spore-forming animal parasites • Apical complex is a unique arrangement of organelles at one end of the cell – Enables the cell to invade its host • Plasmodium causes malaria – Complex life cycle – sexual, asexual, different hosts – Eradication focused on eliminating mosquito vector, drug development, vaccines • DDT-resistant mosquitoes 26 Other apicomplexans • Toxoplasma gondii – Causes infections in humans with immunosuppression – Can cross placental barrier to harm fetus 400x © Carolina Biological Supply Company/Visuals Unlimited Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10 µm © Prof. David J.P. Ferguson, Oxford University 28 Ciliates • 3rd group of apicomplexans • Feature large numbers of cilia arranged in longitudinal rows or spirals around the cell • Pellicle – tough but flexible outer covering • 2 types of nuclei – Micronucleus – without will reproduce asexually – Macronucleus – essential for function • Have two types of vacuoles – Food vacuoles – digestion of food – Contractile vacuoles – regulation of water balance 29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anterior contractile vacuole Macronucleus Micronucleus Cytoproct Posterior contractile vacuole Food vacuole Gullet Cilia Pellicle 30 • This process doesn’t result in more paramecium, but does result in genetic variation Stramenopila • Includes brown algae, diatoms, and oomycetes • Very fine hairs on their flagella – A few species have lost their hairs during evolution 32 Brown algae • Conspicuous seaweeds of northern regions • Life cycle involves alternation of generations – Sporophyte – multicellular and diploid – Gametophyte – multicellular and haploid • Not plants 33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Zygote (2n) Sperm Developing sporophyte Egg Gametophytes (n) n 2n Germinating zoospores Zoospores (n) Sporophyte (2n) 34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Raphe 5 µm 10 µm © Dennis Kunkel/Phototake © Andrew Syred/Photo Researchers, Inc. • Diatoms – Phylum Chrysophyta – Photosynthetic, unicellular organisms – Unique double shells made of silica – Some move using raphes • Two long grooves lined with vibrating fibrils 35 Oomycetes • • • • “Water molds” Either parasites or saprobes Were once considered fungi Motile zoospores with two unequal flagella – Produced asexually • Undergo sexual reproduction • Found in water or on land • Phytophthora infestans – Irish potato famine (1845–1847) – 400,000 people died 36 ARCHAEPLASTIDA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rhizaria Chromalveolata Opisthokonta • These photosynthetic organisms acquired their chloroplast through primary endosymbiosis 37 Animals Choanoflagellida Fungi Amoebozoa Euglenozoa Parabasalids Diplomonads Land plants Charophytes Chlorophytes Cercozoa Rhodophyta Radiolara Foraminifera Brown algae Diatoms Ciliates Amoeboza Stramenopila Oomycetes Dinoflagellates Apicomplexans • This group consists of Rhodophyta, Chlorophyta, Charophytes, and land plants Alveolata Archaeplastida Excavata Rhodophyta • Red algae range from microscopic to very large • Lack flagella and centrioles • Have accessory photosynthetic pigments within phycobilisomes • Origin has been a source of controversy – Tentatively, treated as a sister clade of Chlorophyta (green algae) 38 Red algae 39 Green Algae • Land plants arose from an ancestral green alga only once during evolution • Green alga consist of 2 monophyletic groups – Chlorophyta – Charophytes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5 µm © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited 40 • Unicellular chlorophytes – Early green algae probably resembled Chlamydomonas reinhardtii – Diverged from land plants over 1 BYA • Several lines of evolutionary specialization derived from chlorophytes 41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – Gamete Asexual reproduction +Gamete Pairing of positive and negative mating strains MITOSIS – Strain MITOSIS n + Strain 2n FERTILIZATION Zygospore (diploid) Chlamydomonas life cycle. 42 • Cell specialization in colonial chlorophytes – Multicellularity arose many times in the eukaryotes – Colonial chlorophytes are examples of cellular specialization • Volvox - hollow sphere made up of a single layer of 500 to 60,000 individual cells each with 2 flagella Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vegetative cells Reproductive cells 43 20 nm © Wim van Egmond/Visuals Unlimited • Haplodiplontic life cycles in multicellular chlorophytes – Ulva • Multicellular chlorophyte • Identical gametophyte and sporophyte generations • Consist of flattened sheets two cells thick Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 44 © Dr. Diane S. Littler Haplodiplontic Life Cycle • Multicellular diploid stage – sporophyte – Produces haploid spores by meiosis – Diploid spore mother cells (sporocytes) undergo meiosis in sporangia • Produce 4 haploid spores • First cells of gametophyte generation • Multicellular haploid stage – gametophyte – Spores divide by mitosis – Produces gametes by mitosis – Gametes fuse to form diploid zygote • First cell of next sporophyte generation 45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gametangia Gametophyte (n) Gametes + +Gametangia +Gametophyte (n) Zygote n 2n Germinating zygote Spores Sporophyte (2n) Sporangia Life cycle of Ulva 46 • Charophytes distinguished from chlorophytes by phylogenetic relationship to land plants – Molecular evidence from rRNA and DNA sequences Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chara Coleochaete 45 µm (left): © Dr. John D. Cunningham/Visuals Unlimited; (right): © Dr. Charles F. Delwiche, University of Maryland 47 RHIZARIA Rhizaria Chromalveolata Archaeplastida Excavata Amoeboza Opisthokonta 48 Animals Choanoflagellida Fungi Amoebozoa Euglenozoa Parabasalids Land plants Diplomonads Charophytes Chlorophytes Rhodophyta Cercozoa Radiolara Foraminifera Brown algae Diatoms Stramenopila Oomycetes Ciliates Dinoflagellates Alveolata Apicomplexans • Rhizaria use pseudopods for locomotion • Three distinct monophyletic groups: Radiolara, Foraminifera, and Cercozoa Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Actinopoda (Radiolarians) • Glassy exoskeletons made of silica • Needlelike pseudopods Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10x © Wim van Egmond/Visuals Unlimited Actinosphaerium 49 Foraminifera – Heterotrophic marine protists – Pore-studded shells called tests, through which thin podia emerge – Use podia for swimming and feeding – Complex life cycles with haploid and diploid generations – Limestones are rich in forams • White Cliffs of Dover 50 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © KAGE-Mikrofotografie 8 µm 51 Cercozoa • A morphologically diverse group of primarily soil protists – Locomotiom with flagella or pseudopods – Some have silica-based shells made of scales or plates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Paulinella chromatophora 10 µm © D. J. Patterson, used under license to MBL (micro*scope). Reprinted from John M. Archibald, “Endosymbiosis: double-take on plastid origins,” Current Biology, 16(17):R690-2 © 5 September 2006. With permission from Elsevier 52 AMOEBAZOANS • Amoebas move by means of pseudopods – Pseudopods are flowing projections of cytoplasm • Extend and pull the amoeba forward • Engulf food particles – An amoeba puts a pseudopod forward and then flows into it 53 • Most amoeba are free living – Found in the soil as well as freshwater – Some are parasitic • Acanthomoeba enters the body through a wound and crosses the blood-brain barrier into the brain Amoeba proteus 54 60 µm © Eye of Science/Photo Researchers, Inc. • Slime molds – Were once considered fungi – Include two lineages – Plasmodial slime molds • Huge, single-celled, multinucleate, oozing masses – Cellular slime molds • Single cells combine and differentiate, creating an early model of multicellularity 55 • Plasmodial slime molds – Stream along as a plasmodium • Nonwalled, multinucleate mass of cytoplasm • Form called feeding phase – Ingests bacteria and other organic material – When food or moisture is scarce, organism forms sporangia, where spores are produced 56 • Cellular slime molds – Important group for the study of cell differentiation because of their relatively simple developmental systems – Individual organisms behave as separate amoebas – Move through soil ingesting bacteria – When food is scarce, organisms aggregate to form a slug – Slug differentiates into a sporocarp Asis.org 57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6 5 4 3 2 1 .25 mm © Mark J. Grimson and Richard L. Blanton, Biological Sciences Electron Microscopy Laboratory, Texas Tech University Development in Dictyostelium discoideum, a cellular slime mold. 58 OPISTHOKANTS • Includes choanoflagellates, fungi, and animals • Choanoflagellates – Unicellular organisms – Fungi and animal common ancestor • most like the common ancestor of Sponges – Propulsion by a single posterior flagellum 59 Animals Choanoflagellida Amoeboza Fungi Excavata Amoebozoa Euglenozoa Parabasalids Archaeplastida Diplomonads Land plants Charophytes Chlorophytes Rhizaria Rhodophyta Cercozoa Foraminifera Chromalveolata Radiolara Brown algae Diatoms Oomycetes Ciliates Apicomplexans Dinoflagellates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Opisthokonta Alveolata Stramenopila 60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Colonial choanoflagellates resemble their close animal relatives, the sponges 30 µm © William Bourland, image used under license to MBL 61
