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BIO153 Ch 32 Notes.pdf

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University of Toronto Mississauga
Christoph Richter

Freeman, Biological Science, 4e, Chapter 32 Chapter 32 - An Introduction to Animals Learning Objectives: Students should be able to ... • Define what makes an animal an animal. • Describe the fundamental changes in morphology and development that occurred as animals diversified (symmetry, cephalization, germ layers, limbs, etc.). • Place the major lineages of animals correctly on a phylogenetic tree. • List several examples of the diversity that animals have evolved in adaptations for senses, feeding, movement, and reproduction. Lecture Outline • Defining traits of animals o Animals are the only multicellular heterotrophs that ingest their food. o All animals move under their own power at some point in their life. o All animals other than sponges have neurons and muscle cells. I. Why Do Biologists Study Animals? A. Animals are fascinating. 1. Many biologists study animals simply because animals are inherently interesting. Example: ants. (Fig. 32.1) B. Biological importance 1. Animals are key consumers in virtually every ecosystem. 2. Animals are the most species-rich and diverse multicellular lineage of organisms. C. Role in human health and welfare 1. Animals are very important in many human cultures as sources of food, raw materials, and transportation. a. Examples: fish, mollusks, crustaceans, bee pollination of fruit crops, wool, leather, horses, oxen. 2. Some animals transmit diseases to humans. a. Examples: mosquitoes transmit malaria; rats transmit bubonic plague. 3. Animals as model organisms a. Humans share extensive genetic and physiological homologies with other animals, and research on other animals illuminates human biology questions as well. b. Examples: fruit fly, zebrafish, mice, rats, primates. II. How Do Biologists Study Animals? A. How many types of animals are there? 1. Animals include at least 30 phyla that have distinct morphological differences. (Table 32.1) B. Analyzing comparative morphology 1. Animals have evolved differences in four fundamental aspects of the body plan: a. Presence of tissues, especially the tissues found in embryos © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 32 b. Nervous system and head region c. A fluid-filled body cavity d. The nature of embryonic development 2. The origin and diversification of tissues a. All animals have tissues, which are groups of similar cells organized into structural and functional units. (1) Sponges have historically been thought to lack tissues, but recent research shows that some sponges have epithelium. b. All other animals have at least two different types of tissues that are derived from germ layers, tissue layers in the embryo. (1) There are three germ layers: (i) Endoderm gives rise to the lining of the digestive tract. (ii) Ectoderm gives rise to the skin and nervous system. (iii)Mesoderm gives rise to the circulatory system, muscles, and internal structures such as bone and most organs. (2) Diploblasts have two germ layers: ectoderm and endoderm. (Fig. 32.2) (i) Cnidaria and Ctenophora are traditionally considered diploblasts, but recent data indicate that some cnidarians have mesoderm. (Fig. 32.3) (3) Triploblasts have three germ layers: ectoderm, endoderm, and mesoderm. (i) All animals other than cnidarians, ctenophores, and sponges are triploblasts. 3. Nervous systems, body symmetry, and cephalization a. Sponges have no neurons, no well-defined symmetry, and no head region. b. Cnidarians and ctenophores have a nerve net and radial symmetry, but no head region. (Fig. 32.4a) (1) These animals are equally likely to encounter prey and other environmental stimuli from any direction. c. All other animals (i.e., the triploblasts) have bilateral symmetry, a head region, and a central nervous system (CNS) with ganglia. (Fig. 32.4b) (1) They tend to move in one direction and thus to encounter environmental stimuli at only one end. (2) Evolution of bilateral symmetry is associated with cephalization: evolution of a head region that contains sensing, feeding, and information-processing structures, such as eyes, mouth, and brain. (3) This is an efficient design for directed movement, hunting, and capturing food. 4. Evolution of a body cavity a. Many triploblasts have a fluid-filled internal cavity called a coelom. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 32 (1) The few triploblasts that do not have a coelom are called acoelomates. (Fig. 32.5a) (2) Those that do have a coelom are called coelomates. (Fig. 32.5b) b. The coelom serves as a hydrostatic skeleton that facilitates movement in animals that don't have limbs. Example: roundworms. (Fig. 32.6) c. Students should be able to model the coelom with a long, tube-shaped water balloon, using their fingers to pinch each side and simulate muscle contractions. 5. Protostome and deuterostome patterns of development a. Bilaterians (triploblastic, bilaterally symmetric animals) can be split into two subgroups: protostomes and deuterostomes. b. Protostome development (1) The mouth forms first during gastrulation. (Fig. 32.7a) (2) The coelom forms via splitting of blocks of mesoderm. c. Deuterostome development (1) The anus forms first during gastrulation. (2) The coelom forms via mesoderm pinching off from the gut. (Fig. 32.7b) d. These represent two ways of achieving the same end—a bilaterally symmetric body that contains a cavity lined with mesoderm. 6. The tube-within-a-tube design a. 99% of animal species alive today are bilaterally symmetric, coelomate triploblasts with a tube-within-a-tube body design. (1) The inner tube is the gut, the outer tube is the body wall, and the mesoderm forms between the tubes. (Fig. 32.8a) b. Worms are a variety of different lineages that all have a simple tube-within-a-tube design. (Fig. 32.8b) c. Once the tube-within-a-tube body plan evolved, the diversification of animals was fueled by the evolution of specialized structures for moving, capturing food, and sensing the environment. 7. Students should be able to explain why triploblasty, bilateral symmetry, and a coelom add up to produce a tube-within-a- tube body design. They should also be able to explain why cephalization was important. C. Evaluating molecular phylogenies 1. Beginning in 1997 with Anna Marie Aguinaldo's famous rRNA study, genetic analyses have illuminated the relationships among animal phyla. (Fig. 32.9) 2. Choanoflagellates are the closest living relatives of animals. (Fig. 32.10a) 3. Porifera (sponges) are the sister group to all other animals. (Fig. 32.l0b) © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 32 4. Ctenophora and Cnidaria are a monophyletic group and are the sister group to acoelomorphs and bilaterians. 5. Acoelomorphs are the next group to branch off the tree 6. Coelomates then split into protostomes and deuterostomes. 7. Protostomes immediately split into two major groups: ecdysozoans and lophotrochozoans. a. Ecdysozoans grow by shedding their outer skeletons. b. Lophotrochozoans grow by extending the size of their skeletons. 8. Segmentation evolved several times independently: in protostomes (annelids, arthropods, and probably mollusks) and deuterostomes. 9. Flatworms (Platyhelminthes) lost the coelom secondarily. 10.One group of deuterostomes re-evolved radial symmetry⎯adult echinoderms. 11.Vertebrates are a monophyletic group that is defined by the presence of a skull. 12.Invertebrates are a paraphyletic group. III. What Themes Occur in the Diversification of Animals? A. Major lineages of animals are defined by a particular body plan, but subsequent diversification within a lineage was typically triggered by innovations in sensing, feeding, and movement. B. Sensory organs 1. Variation in sensory abilities a. Most animals have senses of touch, balance, smell, taste, and hearing, and at least some ability to sense light and time. b. Some animals evolved abilities to detect other stimuli such as magnetism, electric fields, and barometric pressure. 2. Variation in sensory structures a. Animals vary greatly in the complexity and abilities of a given sensory structure. Example: eyes in mollusks. (Fig. 32.11) C. Feeding 1. How animals feed: four general tactics a. Animals have variation in mouthpart structures, and this correlates closely with how they eat. b. Suspension feeders (filter feeders) capture food by filtering particles out of water or air. (1) Examples: sponges, clams and mussels, baleen whales. (2) They are common in aquatic habitats and in sessile organisms. c. Deposit feeders eat their way through a substrate on the surface. (1) Examples: annelids (earthworms), sea cucumbers. (Fig. 32.12) (2) All have simple mouthparts and a wormlike body shape. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 32 d. Fluid feeders suck or mop up liquids (nectar, plant sap, blood, fruit juice). (1) Examples: butterflies, blow flies. (Fig. 32.13) e. Mass feeders take chunks of food into their mouths. (1) Examples: horses, snails. (Fig. 32.14) (2) Mouthparts vary according to the type of food eaten. 2. What animals eat: three general sources a. Herbivores eat plants or algae, carnivores eat animals, and detritivores eat dead or decaying matter
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