chapt32_lecture.pdf

2 General Features of Animals Heterotrophy - obtain energy and organic molecules by ingesting other organisms Multicellularity - Many have complex bodies No cell walls - They lack rigid cell walls and are usually flexible Active movement - Move more rapidly and in more complex ways (motility) Divers...

2 General Features of Animals Heterotrophy - obtain energy and organic molecules by ingesting other organisms Multicellularity - Many have complex bodies No cell walls - They lack rigid cell walls and are usually flexible Active movement - Move more rapidly and in more complex ways (motility) Diversity of form - Vary greatly in form, ranging in size from organisms too small to see with the unaided eye to enormous (shape and size) ANIMAL DIVERSITY AND THE EVOLUTION OF BODY PLANS Chapter 33 1 2 3 4 Evolution of the Animal Body Plan Diversity of habitat - Grouped into 35–40 phyla, most that occur only in the sea but many occur in fresh water and on land Sexual reproduction - Most animals reproduce sexually. Animal eggs, which are nonmobile. Embryonic development - Zygote first undergoes a series of mitotic divisions that produces a ball of cells Tissues - Cells of most animals are organized into structural and functional units called tissues (development) Five key transitions can be noted in animal evolution 1. 2. 3. 4. 5. 3 Symmetry Tissues Body cavity Patterns of Development Segmentation 4 5 6 1. Evolution of symmetry Sponges also lack any definite symmetry ̶ Eumetazoa have a symmetry defined along an imaginary axis drawn through the animal’s body ̶ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bilaterally symmetrical animals have two main advantages over radially symmetrical ones 1. Cephalization 8 Radial Symmetry Comparison of Two main types of symmetryradial and bilateral Radial symmetry symmetry Body parts arranged around central axis ̶ Can be bisected into two equal halves in any 2-D plane ̶ 2. Evolution of tissues a. ̶ 5 Body has right and left halves that are mirror images Only the sagittal plane bisects the animal into two equal halves Parazoa (Sponges – the simplest animals) lack defined tissues and organs ̶ Bilateral Symmetry Top Dorsal Sagittal plane Back Have the ability to disaggregate and aggregate their cells Posterior Bilateral symmetry ̶ Evolution of a definite brain area ̶ 2. Greater mobility Frontal plane Front Anterior Ventral b. ̶ Transverse plane Bottom Eumetazoa (all other animals) have distinct and welldefined tissues ̶ Have irreversible differentiation for most cell types 6 1 7 3. Evolution of a body cavity ̶ Eumetazoa produce three germ layers ̶ Outer ectoderm (body coverings and nervous system) ̶ Middle mesoderm (skeleton and muscles) ̶ Inner endoderm (digestive organs and intestines) 8 The body cavity made possible the development of advanced organ systems ̶ Coelomates developed a circulatory system to flow nutrients and remove wastes ̶ Open circulatory system: blood passes from vessels into sinuses, mixes with body fluids, and reenters the vessels ̶ Closed circulatory system: blood moves continuously through vessels that are separated from body fluids ̶ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13 Acoelomate Ectodermally derived tissue Endodermally derived tissue Digestive cavity Mesodermally derived tissue Flatworm Pseudocoelomate Three body plans Endodermally derived tissue Body cavity = Space surroundedfor bybilaterally mesoderm symmetrical tissue that is formed during development Ectodermally derived tissue Digestive cavity animals Three basic kinds of body plans ̶ Acoelomates = No body cavity ̶ Pseudocoelomates = Body cavity between mesoderm and endoderm Called the pseudocoelom ̶ Coelomates = Body cavity entirely within the mesoderm Called the coelom Roundworm 4. Evolution of different patterns of development Mesodermally derived tissue Pseudocoelom -The basic Bilaterian pattern of development: - Mitotic cell divisions of the egg form a hollow ball of cells, called the blastula - Blastula indents to form a two-layer-thick ball with: Coelomate Ectodermally derived tissue Endodermally derived tissue Digestive cavity Annelid Mesodermally derived tissue Coelom - Blastopore = Opening to outside - Archenteron = Primitive body cavity 7 8 9 Bilaterians can be divided into two groups: Fate of Embryonic Cells Four-cell embryo Anus (if present) develops either from blastopore or another region of embryo Deuterostomes develop the anus first from the blastopore Mouth develops later from another region of the embryo Spiralian Protostomes Protostomes develop the mouth first from or near the blastopore ̶ Blastopore becomes mouth Formation of Coelom Archenteron Cell excised Mouth Top view Mesoderm Development arrested Spiral cleavage Deuterostomes differ from protostomes in three other fundamental embryological features: Fate of Blastopore Determinate development Axis Side view Four-cell embryo 1. Cleavage pattern of embryonic cells ̶ Protostomes = Spiral cleavage Indeterminate development Mesoderm ̶ Protostomes = Determinate development ̶ Deuterostomes = Indeterminate development Axis Blastopore becomes anus Side view Archenteron Top view Radial cleavage 9 Coelom Anus Cell excised Deuterostomes ̶ Deuterostomes = Radial cleavage 2. Developmental fate of cells 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cleavage Normal embryos 10 11 12 Traditional Classification of Animals 5. Evolution of segmentation - Segmentation provides two advantages 1. Allows redundant organ systems in adults such as occurs in the annelids 2. Allows for more efficient and flexible movement because each segment can move independently Segmentation appeared several times in the evolution of animals 11 Multicellular animals, or metazoans, are traditionally divided into 36 or so distinct phyla based on shared anatomy and embryology Metazoans are divided into two main branches: Parazoa = Lack symmetry and tissues Eumetazoa = Have symmetry and tissues - Diploblastic = Have two germ layers - Triploblastic = Have three germ layers 12 2 13 13 14 14 15 15 16 16 17 18 Current Phylogeny Most new phylogenies agree on two revolutionary features: 1. Separation of annelids and arthropods into different clades 2. Division of the protostome group into Ecdysozoa and Spiralia The traditional animal phylogeny is being reevaluated using molecular data Animal phylogeny developed from morphological, molecular, life history, and other types of relevant data 17 Some parts of this phylogeny are not firmly established New studies are constantly appearing, often with somewhat different conclusions Key morphological characters used in traditional classification are not necessarily conservative Molecular systematics uses unique sequences within certain genes to identify clusters of related groups ̶ The latter is then broken down into Lophotrochozoa and Platyzoa 18 3 31 Porifera Parazoa Animals lacking tissues (and therefore organs) and a definite symmetry 7000 marine species; 150 freshwater species Among the most abundant 20 animals in the deep Modern Phylogeny Parazoa Acoelomorpha Platyhelminthes Bryozoa Brachiopoda Cycliophora Micrognathozoa Rotifera Parazoa 32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. animals in the deep ocean Larval sponges free-swimming Kinorhyncha Loricifera Nemertea Mollusca Bryozoa Brachiopoda Cycliophora Platyhelminthes Rotifera Acoela Micrognathozoa Ctenophora Cnidaria Annelida Protista Choanoflagellates Porifera Pseudocoelom Lophotrochozoa freshwater species symmetry Various growth forms Among the most abundant Lophotrochozoa Adults remain attached – Most members lacksessile symmetry Cell types Various growth forms Truly multicellular Larval sponges free-swimming 3 functional layers in vase Adults remain attached – sessile Cell types Truly multicellular 3 functional layers in “vase” Pseudocoelom Acoelom ate Spiralia Most members lack Spiralia Platyzoa Protostomes Platyzoa 7000 marine species; 150 Eum etazoa Protostom es m orpha Eumetazoa Ctenophora Parazoa Animals lacking tissues (and therefore organs) and a definite symmetry Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cnidaria They consist of fewer phyla and species than protostomes They are more uniform in many ways, despite great differences Acoelo- ocean Porifera Deuterostomes include chordates and echinoderms Porifera Acoela 19 Molting Spiral cleavage Coelom Bilateria Metazoa a. 19 © Andrew J. Martinez/Photo Researchers, Inc. 20 21 22 34 3 layers 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Osculum Water Outer epithelium Amoebocyte Water comes in ostia, exits osculum 2. Pore Asexual Sexual Fragmentation Spongin fiber Choanocytes transform into sperm Spicule Ostium Sperm captured and passed to egg cell in mesohyl Development may occur within mother or in open water Larva is planktonic; will settle and transform into adult Choanocyte carbonate Spongin – reinforcing tough protein fibers Sponge reproduction Choanocyte Mesohyl Middle layer – gelatinous matrix Spicules – needles of calcium Epithelial wall Flagellum Collar b. Nucleus 3. Choanocytes Collar cells Flagellated – contributes to water circulation Face internal cavity Engulf and digest food from passing water 21 22 23 24 38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inner endoderm forms the gastrodermis Outer ectoderm forms the epidermis and nervous system Middle mesoderm (only in bilateral animals) forms the muscles Bodies have distinct tissues but no organs No concentrated nervous system Radial symmetry Bilateral symmetry Protostomes Acoelomorpha Spiralia Bryozoa Brachiopoda Lophotrochozoa Platyhelminthes Cycliophora Rotifera Platyzoa Micrognathozoa Acoela Most marine, few fresh water species Diploblastic True body symmetry 23 Ctenophora Animals with distinct tissues Embryos have distinct layers Cnidaria Phylum Cnidaria Porifera Eumetazoa Parazoa Eumetazoa No reproductive, circulatory, or excretory systems Latticework of nerve cells Touch, gravity, light receptors 24 4 25 26 Cnidarians use nematocysts to capture prey Secreted within nematocyte Mechanism of discharge unknown Some carry venom Body plan has single opening leading to gastrovascular cavity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mouth Tentacles Gastrodermis Epidermis Nematocyte Site of digestion / Most gas exchange / Waste discharge / Formation of gametes in many 2 layers to body wall Trigger Undischarged nematocyst 1. Epidermis 2. Gastrodermis 3.3 mm Hydra Mesoglea Nematocyte with nematocyst Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gastrovascular cavity (inset): © Roland Birke/Phototake Gastrovascular space also serves as hydrostatic skeleton Provides a rigid structure against which muscles can operate Gives the animal shape Many polyp species build an exoskeleton of chitin or calcium carbonate around themselves Some build an internal skeleton Mesoglea Cnidarians use nematocysts to capture prey Gastrodermis Epidermis Mouth Secreted 2 –basic body within forms nematocyte Mechanism of discharge unknown –Polyps – cylindrical and sessile –Medusa – umbrella-shaped and freeSome carry venom living - Mesoglea between layers Tubule Discharged nematocyst Sensory cell Tentacles Gastrodermis 40 Gastrovascular cavity Mesoglea Epidermis Mouth Medusa Polyp 2 basic body forms 25 26 – Polyps – cylindrical and sessile – Medusa – umbrella-shaped and free-living 41 27 28 4 or 5 classes Cnidarian life cycle Some cnidarians occur only as polyps, and others exist only as medusae, but many alternate between these two phases 1. In general, in species having both polyp and medusa in the life cycle, the medusa forms gametes Symbiotic dinoflagellates (zooxanthellae) photosynthesize and provide nutrients to reef coral Coral reefs economically important Sexes separate Gonochorism – individual is either male or female Zygote develops into planktonic planula Metamorphosis into polyp Polyp produces medusae or other polyps asexually 2. Cubozoa Box jellies Strong swimmers, voracious fish Major evolutionary innovation in cnidarians is extracellular digestion of food inside the animal predators Stings may be fatal to humans Digestion takes place partly in gastrovascular cavity Cells then engulf fragments by phagocytosis 27 Anthozoa Sea anemones, most corals, sea fans Solitary and colonial polyps Both phases consist of diploid individuals 28 29 30 Phylum Ctenophora Hydrozoa 3. Hydroids, Hydra, Portuguese man-of-war Known as comb jellies, sea Both polyp and medusa stages walnuts, or sea gooseberries Only class with freshwater members 29 Eumetazoa Acoelomorpha Spiralia Platyhelminthes Brachiopoda Lophotrochozoa Bryozoa Cycliophora Platyzoa Rotifera capture prey Protostomes Micrognathozoa Discharge strong adhesive used to Acoela 49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parazoa 5. fused cilia that beat in a coordinated fashion Many bioluminescent 2 tentacles covered with colloblasts Ctenophora 8 rows of comblike plates of Cnidaria Scyphozoa Jellyfish Medusa more conspicuous and complex Ring of muscle cells allows for rhythmic contractions for propulsion Staurozoa Star jellies Resembles a medusa in most ways but is attached to the substratum by a sort of stalk that emerges from the side opposite the mouth Porifera 4. Phylogenetic position unclear 30 5 31 32 The Bilaterian Acoelomates Phylum Acoelomorpha Characterized by bilateral symmetry Allowed for high levels of specialization Acoel flatworms were once considered basal members of the phylum Platyhelminthes Have a primitive nervous system and lack a digestive cavity Bilaterians are traditionally classified by the condition of their coelom 31 Protostomes Based on molecular evidence, similarities are convergent Spiralia Bryozoa Platyhelminthes Lophotrochozoa Brachiopoda Cycliophora Rotifera Platyzoa Micrognathozoa Acoela Ctenophora Cnidaria Acoelomorpha Parazoa Eumetazoa Porifera Acoelomates Pseudocoelomates Coelomates 51 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 32 6