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16/04/12 Overview: Welcome to Your Kingdom An Overview of Animal Diversity & Introduc>on to Development • The animal kingdom extends far beyond humans and other animals we may encounter • Scientists have identified 1.3 million living species of animals Chapter 32 Animation: Coral Reef © 2011 Pearson Education, Inc. Figure 32.1 Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers • There are exceptions to nearly every criterion for distinguishing animals from other life-forms • Several characteristics, taken together, sufficiently define the group © 2011 Pearson Education, Inc. 1 16/04/12 Nutritional Mode • Animals are heterotrophs that ingest their food © 2011 Pearson Education, Inc. Cell Structure and Specialization • Animals are multicellular eukaryotes • Their cells lack cell walls • Their bodies are held together by structural proteins such as collagen • Nervous tissue and muscle tissue are unique, defining characteristics of animals • Tissues are groups of cells that have a common structure, function, or both © 2011 Pearson Education, Inc. Figure 32.2-3 Reproduction and Development • Most animals reproduce sexually, with the diploid stage usually dominating the life cycle • After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage • Cleavage leads to formation of a multicellular, hollow blastula • The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues Zygote Cleavage Blastocoel Cleavage Eight-‐cell stage Blastula Cross sec5on of blastula Gastrula5on Blastocoel Endoderm Ectoderm Archenteron Video: Sea Urchin Embryonic Development Cross sec5on of gastrula Blastopore © 2011 Pearson Education, Inc. 2 16/04/12 • Many animals have at least one larval stage • A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis • A juvenile resembles an adult, but is not yet sexually mature © 2011 Pearson Education, Inc. • Most animals, and only animals, have Hox genes that regulate the development of body form • Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology © 2011 Pearson Education, Inc. Figure 32.3 Concept 32.2: The history of animals spans more than half a billion years Choanoflagellates OTHER EUKARYOTES Sponges Animals • The animal kingdom includes a great diversity of living species and an even greater diversity of extinct ones • The common ancestor of living animals may have lived between 675 and 800 million years ago • This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals Individual choanoflagellate Other animals Collar cell (choanocyte) © 2011 Pearson Education, Inc. 3 16/04/12 Figure 32.4a Neoproterozoic Era (1 Billion–542 Million Years Ago) 1.5 cm • Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago (a) Mawsonites spriggi © 2011 Pearson Education, Inc. Figure 32.4b 0.4 cm Paleozoic Era (542–251 Million Years Ago) • The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals • There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota (b) Spriggina floundersi – New predator-prey relationships – A rise in atmospheric oxygen – The evolution of the Hox gene complex © 2011 Pearson Education, Inc. 4 16/04/12 Figure 32.5 • Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions • Animals began to make an impact on land by 460 million years ago • Vertebrates made the transition to land around 360 million years ago © 2011 Pearson Education, Inc. Mesozoic Era (251–65.5 Million Years Ago) • Coral reefs emerged, becoming important marine ecological niches for other organisms • The ancestors of plesiosaurs were reptiles that returned to the water • During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates • The first mammals emerged • Flowering plants and insects diversified © 2011 Pearson Education, Inc. Cenozoic Era (65.5 Million Years Ago to the Present) • The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals • These extinctions included the large, nonflying dinosaurs and the marine reptiles • Mammals increased in size and exploited vacated ecological niches • The global climate cooled © 2011 Pearson Education, Inc. 5 16/04/12 Concept 32.3: Animals can be characterized by body plans RESULTS 1 Early stages of development • Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits • Some developmental characteristics are conservative 100 µm Figure 32.6 2 32-‐cell stage Site of gastrula5on 3 Early gastrula stage - For example, the molecular control of gastrulation is conserved among diverse animal groups Site of gastrula5on 4 Embryos with blocked β-‐catenin ac5vity © 2011 Pearson Education, Inc. Figure 32.6b 100 µm Figure 32.6a Early stage of development Site of gastrula5on 32-‐cell stage 6 16/04/12 Figure 32.6c Figure 32.6d Site of gastrula5on Embryos with blocked β-‐catenin ac5vity Early gastrula stage Figure 32.7 Symmetry • Animals can be categorized according to the symmetry of their bodies, or lack of it • Some animals have radial symmetry, with no front and back, or left and right (a) Radial symmetry (b) Bilateral symmetry © 2011 Pearson Education, Inc. 7 16/04/12 • Two-sided symmetry is called bilateral symmetry • Bilaterally symmetrical animals have – A dorsal (top) side and a ventral (bottom) side – A right and left side – Anterior (head) and posterior (tail) ends – Cephalization, the development of a head © 2011 Pearson Education, Inc. • Radial animals are often sessile or planktonic (drifting or weakly swimming) • Bilateral animals often move actively and have a central nervous system © 2011 Pearson Education, Inc. Tissues • Animal body plans also vary according to the organization of the animal s tissues • Tissues are collections of specialized cells isolated from other tissues by membranous layers • During development, three germ layers give rise to the tissues and organs of the animal embryo © 2011 Pearson Education, Inc. • Ectoderm is the germ layer covering the embryo s surface • Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron © 2011 Pearson Education, Inc. 8 16/04/12 Body Cavities • Sponges and a few other groups lack true tissues • Diploblastic animals have ectoderm and endoderm – These include cnidarians and comb jellies • Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians • Most triploblastic animals possess a body cavity • A true body cavity is called a coelom and is derived from mesoderm • Coelomates are animals that possess a true coelom – These include flatworms, arthropods, vertebrates, and others © 2011 Pearson Education, Inc. Figure 32.8 © 2011 Pearson Education, Inc. Figure 32.8a (a) Coelomate Coelom Diges5ve tract (from endoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) (a) Coelomate Coelom (b) Pseudocoelomate Body covering (from ectoderm) Pseudocoelom Diges5ve tract (from endoderm) Muscle layer (from mesoderm) Diges5ve tract (from endoderm) (c) Acoelomate Body covering (from ectoderm) Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Tissue-‐ filled region (from mesoderm) Wall of diges5ve cavity (from endoderm) 9 16/04/12 Figure 32.8b • A pseudocoelom is a body cavity derived from the mesoderm and endoderm • Triploblastic animals that possess a pseudocoelom are called pseudocoelomates (b) Pseudocoelomate Body covering (from ectoderm) Pseudocoelom Diges5ve tract (from endoderm) Muscle layer (from mesoderm) © 2011 Pearson Education, Inc. Figure 32.8c • Triploblastic animals that lack a body cavity are called acoelomates (c) Acoelomate Body covering (from ectoderm) Tissue-‐ filled region (from mesoderm) Wall of diges5ve cavity (from endoderm) © 2011 Pearson Education, Inc. 10 16/04/12 Protostome and Deuterostome Development • Coelomates and pseudocoelomates belong to the same grade • A grade is a group whose members share key biological features • A grade is not necessarily a clade, an ancestor and all of its descendents © 2011 Pearson Education, Inc. • Based on early development, many animals can be categorized as having protostome development or deuterostome development © 2011 Pearson Education, Inc. Figure 32.9 Cleavage • In protostome development, cleavage is spiral and determinate • In deuterostome development, cleavage is radial and indeterminate • With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo • Indeterminate cleavage makes possible identical twins, and embryonic stem cells Protostome development (examples: molluscs, annelids) (a) Cleavage Deuterostome development (examples: echinoderms, chordates) Eight-‐cell stage Eight-‐cell stage Spiral and determinate Radial and indeterminate (b) Coelom forma5on Coelom Archenteron Coelom Mesoderm Blastopore Blastopore Solid masses of mesoderm split and form coelom. (c) Fate of the blastopore Mesoderm Folds of archenteron form coelom. Anus Mouth Diges5ve tube Key Ectoderm Mesoderm Endoderm Mouth Mouth develops from blastopore. Anus Anus develops from blastopore. © 2011 Pearson Education, Inc. 11 16/04/12 Figure 32.9a Coelom Formation (a) Cleavage Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Eight-‐cell stage Eight-‐cell stage • In protostome development, the splitting of solid masses of mesoderm forms the coelom • In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom Key Ectoderm Mesoderm Endoderm Spiral and determinate Radial and indeterminate © 2011 Pearson Education, Inc. Figure 32.9b Fate of the Blastopore (b) Coelom forma5on Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Coelom Archenteron Coelom Key Ectoderm Mesoderm Endoderm Mesoderm Blastopore Solid masses of mesoderm split and form coelom. Blastopore Mesoderm • The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula • In protostome development, the blastopore becomes the mouth • In deuterostome development, the blastopore becomes the anus Folds of archenteron form coelom. © 2011 Pearson Education, Inc. 12 16/04/12 Figure 32.9c (c) Fate of the blastopore Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth Diges5ve tube Key Ectoderm Mesoderm Endoderm Mouth Mouth develops from blastopore. Anus Anus develops from blastopore. Concept 32.4: New views of animal phylogeny are emerging from molecular data • Zoologists recognize about three dozen animal phyla • Phylogenies now combine morphological, molecular, and fossil data • Current debate in animal systematics has led to the development of multiple hypotheses about the relationships among animal groups © 2011 Pearson Education, Inc. Figure 32.10 Porifera Cnidaria Eumetazoa Metazoa Ctenophora Protostomia Bilateria Deuterostomia • One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons ANCESTRAL COLONIAL FLAGELLATE Ectoprocta Brachiopoda Echinodermata Chordata Platyhelminthes Ro5fera Mollusca Annelida Arthropoda Nematoda © 2011 Pearson Education, Inc. 13 16/04/12 Figure 32.11 Porifera Ctenophora Eumetazoa Metazoa Cnidaria Acoela Bilateria Echinodermata Chordata Platyhelminthes Lophotrochozoa Deuterostomia • One hypothesis of animal phylogeny is based mainly on molecular data ANCESTRAL COLONIAL FLAGELLATE Ro5fera Ectoprocta Brachiopoda Mollusca Ecdysozoa Annelida Nematoda Arthropoda © 2011 Pearson Education, Inc. Points of Agreement 1. All animals share a common ancestor 2. Sponges are basal animals 3. Eumetazoa is a clade of animals (eumetazoans) with true tissues 4. Most animal phyla belong to the clade Bilateria, and are called bilaterians 5. Chordates and some other phyla belong to the clade Deuterostomia © 2011 Pearson Education, Inc. Progress in Resolving Bilaterian Relationships • The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes • In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa • Ecdysozoans shed their exoskeletons through a process called ecdysis © 2011 Pearson Education, Inc. 14 16/04/12 Figure 32.12 • Some lophotrochozoans have a feeding structure called a lophophore • Others go through a distinct developmental stage called the trochophore larva © 2011 Pearson Education, Inc. Figure 32.13 Figure 32.13a Lophophore Apical tu_ of cilia Lophophore Mouth Anus (a) Lophophore feeding structures of an ectoproct (b) Structure of a trochophore larva (a) Lophophore feeding structures of an ectoproct 15 16/04/12 Figure 32.UN01 Future Directions in Animal Systematics • Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history © 2011 Pearson Education, Inc. Figure 32.UN02 Figure 32.UN03 Common ancestor of all animals Metazoa Porifera (basal animals) 565 mya: Ediacaran biota 365 mya: Early land animals Origin and diversifica5on of dinosaurs Ctenophora Diversifica5on of mammals Paleozoic Neoproterozoic 1,000 542 251 Millions of years ago (mya) Mesozoic Ceno-‐ zoic 65.5 Cnidaria True 5ssues Acoela (basal bilaterians) 0 Deuterostomia Bilateral symmetry Three germ layers Lophotrochozoa Bilateria (most animals) Era Eumetazoa 535–525 mya: Cambrian explosion Ecdysozoa 16 16/04/12 Figure 32.UN04 Mnemonic • • • • • • • • • Dumb King Phillip Could Only Find Green Snakes (Sometimes) • • • • • • • • • Domain Kingdom Phylum (Phyla)* Class Order Family Genus (Genera) Species (Sub-species) *In Botany, Phyla are called Divisions 17