Animal Form and Function by Dana Krempels Animalia is characterized by a distinct progression of complexity in form and function. Early in animal evolution, body symmetry, embryonic germ layers, and ontogenetic origins of major anatomical structures diverge as taxa branch from common ancestors. Before you begin this workshop, be sure you are able to 1. List synapomorphies that distinguish animals from all other eukaryotes 2. Understand the meanings of asymmetry, radial and bilateral symmetries 3. Be able to recognize the major animal phyla on the basis of a. body symmetry b. embryonic germ layers (ectoderm, endoderm, mesoderm) c. presence or absence of an internal body cavity d. ontogeny and morphology of the internal body cavity e. ontogenetic differences between protostomes and deuterostomes. 4. Be able to recognize acoelomate, pseudocoelomate and coelomate body plans 5. Distinguish between a. spiral and radial cleavage b. determinate and indeterminate cleavage c. schizocoely and enterocoely To review the items above, go to http://www.bio.miami.edu/dana/160/160s16_15.html A. Ontogenetic and morphological characters present in major animal phyla Note the characters in the table below. Each should be placed on the phylogenetic tree (on the next page) to indicate where it appears in the animals above that character. (Enter only the letters, since there s no room to write the entire character description.) a. lophophore feeding apparatus k. coelom formed via schizocoely b. mesoderm lines parietal side of body wall l. bilateral symmetry c. body cavity contains acellular mesogloea m. radial symmetry d. coelom formed via enterocoely n. cnidoblast stinging cells e. mesoderm derived from endoderm o. true tissues f. body cavity contains cellular mesenchyme p. nervous system embryonically dorsal g. cellular division of labor q. blastopore becomes the mouth h. complete digestive system r. blastopore becomes the anus i. diploblasty s. trochophore larva j. triploblasty t. pseudocoelom a persistent blastocoel Pronunciations: cnidoblast NEE - doh blast coelom SEE lom enterocoely EN - ter - oh - see - lee lophophore LOW - fo-four mesogloea mes - oh GLEE - uh pseudocoelom SUE - doh - see lom schizocoely SKIZ oh see - lee
1. What does the placement of the characters on the phylogenetic tree imply about evolutionary relationships among the Bilateria (bi-luh-tier - ee - uh)? 2. What does the placement of the characters on the phylogenetic tree imply about evolutionary relationships among the Lophotrochozoa (low - fo - tro - ko - ZO uh)? 3. What does the placement of the characters on the phylogenetic tree imply about evolutionary relationships among the Ecdysozoa (eck dee so ZO uh)? 4. Do a Google Image Search of the name each of the following taxa and view photos/videos of them. What is the common name for animals in each of these phyla? For each, indicate whether it is a protostome, deuterostome, or neither. Taxon Name Common name protostome/deuterostome/neither Hexactinellida Calcarea Ctenophora Acoela Cestoda Rotifera Phoronida Bivalvia Hemichordata Urochordata Holothuroidea Priapulida 4. Do another search. List some familiar examples of organisms in each of the following taxa: Anthozoa (Cnidaria) Cestoda (Platyhelminthes) Cephalopoda (Mollusca) Annelida Nematoda Hexapoda (Arthropoda) Arachnida (Arthropoda)
B. Ancestry, Form and Function 1. Consider the synapomorphies common to both protostomes and deuterostomes. Based on this information, what do you think the most recent common ancestor of these organisms might have looked like? What characters did it have? 2. Based on your description of the protostome/deuterostome common ancestor, which organ system(s) in these animals are likely the most primitive? (i.e., which evolved first?) 3. Consider the synapomorphies common to all Ecdysozoans. Based on this information, what do you think the most recent common ancestor of these organisms might have looked like? What characters did it have? 4. Consider the synapomorphies common to all Lophotrochozoans. Based on this information, what do you think the most recent common ancestor of these organisms might have looked like? What characters did it have? 5. List synapomorphies that set animals in each of the following taxa apart from the ancestral Ecdysozoan (and from each other). a. Nematoda b. Arthropoda 6. How does the main body cavity of a nematode differ from that of an arthropod? List at least three key features. 7. List synapomorphies that set animals in each of the following taxa apart from the ancestral Lophotrochozoan (and from each other). a. Mollusca b. Annelida 8. Both Mollusks and Arthropods have (1) an open circulatory system and (2) a reduced
coelom that functions as the pericardium (pear-ee-kar -dee-um) and gonocoel (GONE -oh-seal). If the hypothetical relationships in the tree above are correct, what does this suggest about the evolution of these two characters in these distantly related phyla? a. What defines a true coelom? b. What is a pericardium? c. What is a gonocoel? 9. Consider the synapomorphies common to all Deuterostomes. Based on this information, what do you think the most recent common ancestor of these organisms might have looked like? What characters did it have? 10. List synapomorphies that set animals in each of the following taxa apart from the ancestral Deuterostome (and from each other). a. Echinodermata b. Hemichordata c. Chordata C. Practical Applications 1. A drug called lufenuron (loo-fen -yur-on) interferes with the activity of an enzyme known as chitinase (KAI -tin-ayze), which is involved in the normal formation of chitin (KAI-tin) in growing arthropods. Lufenuron prevents normal maturation of animals that use chitin as structural support, such as in the exoskeleton (arthropods) or a protective cuticle (nematodes) surrounding the skin. Which of the following do you think would most likely be adversely affected by medicating an infected host mammal with lufenuron? a. fleas d. heartworm (a nematode) g. tapeworms b. ear mites e. ringworm fungus h. ticks c. leeches f. liver flukes i. caterpillars 2. It turns out that although lufenuron is effective against insects (Arthropoda, Hexapoda), it
does not kill ticks (Arthropoda, Arachnida). Devise one or more logical hypotheses that might explain this. 3. Animal phyla have long been classified into putatively monophyletic assemblages on the basis of their body plans. However, as more sophisticated molecular techniques (nucleic acid sequencing) have been applied to systematics, it has been discovered that shared morphological characters do not always reflect recent common ancestry. View the phylogenetic trees below. Phylogeny based on morphology Phylogeny based on molecular data Now consider the following: Ivermectin (EYE -ver-mek-tin) is a macrolide (MAK -ro-lide) drug produced from a fungus (Streptomyces avermitilis) first isolated from a soil sample in Japan. Ivermectin is an agonist for the neurotransmitter gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter. (NOTE: an agonist increases the effects of the neurotransmitter, whereas an antagonist reduces the effects.) In mammals, GABA-containing neurons and receptors are found in the Central Nervous System. In arthropods and nematodes GABA is found primarily in the Peripheral Nervous
System. This difference in location of GABA receptors is one reason why ivermectin can be safely administered to (most) mammals for treatment of arthropod and nematode parasites. Here s how ivermectin works: 1. Ivermectin binds to a neuronal membrane, increasing release of GABA 2. GABA binds to the GABA-receptor-chloride channel complex of the postsynaptic neuronal membrane. (Nerve impulses travel from the presynaptic neuron, across the synapse to the postsynaptic neuron.) 3. The binding of ivermectin to the receptor complex causes an influx of chloride ions. 4. The abnormal influx of chloride ions hyperpolarizes the neuronal membrane. 5. The membrane becomes less excitatory 6. Nerve impulse transmission is decreased. The hyperpolarization of neuronal membranes causes a fatal flaccid paralysis (FLA -sid, meaning floppy or loose, as opposed to paralysis caused by permanently contracted muscles) in arthropods and nematodes. Discuss the implications of this response to ivermectin in both arthropods and nematodes. Do you think it is evidence of convergent evolution, or of homology? Explain your answer. Discussion Can you think of other examples of characteristics used to devise phylogenies that might also have relevance in treatment of disease, solution of environmental problems, or other practical applications? Discuss.