Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Today: The Animal Kingdom and Its Traditional Classification Scheme Major Trends in Animal Evolution The Invertebrates and Beyond? “Making the Grade”: Winter College Transfer Fair! Thursday, February 10, 2005 9:00am - 12:30pm The Major Grades: 4 Dichotomies The ParazoaParazoa-Eumetazoa Dichotomy Animals lacking true tissues are called parazoans All other groups have true tissues (eumetazoans) eumetazoans) The Major Grades: 4 Dichotomies The RadiataRadiata-Bilateria Dichotomy Radiata tend to be sessile or planktonic (What’s the advantage??) The Major Grades: 4 Dichotomies The RadiataRadiata-Bilateria Dichotomy The EUMETAZOANS can be separated into two groups based on symmetry Radial symmetry = Radiata Bilateral Symmetry = Bilateria The Major Grades: 4 Dichotomies The RadiataRadiata-Bilateria Dichotomy In contrast the Bilariata have a dorsal (top) and ventral (bottom side), as well as a anterior and posterior end They demonstrate a tendency towards CEPHALIZATION, or the concentration of sensory equipment on the anterior end (important for mobile animals!) 1 The Major Grades: 4 Dichotomies The RadiataRadiata-Bilateria Dichotomy In addition, the Radiata are DIPLOBLASTIC (two GERM Layers) The ECTODERM (outer layers, nervous system in some) The ENDODERM (innermost layer, gives rise to the digestive tract related organs) The Major Grades: 4 Dichotomies The Acoelomate, Acoelomate, Pseudocoelomate and Coelomate Grades The simplest Bilateria have solid bodies (no cavity between the digestive tract and outer body wall) and are acoelomates (“without hollow”) The Major Grades: 4 Dichotomies The RadiataRadiata-Bilateria Dichotomy The Bilateria are TRIPLOBLASTIC and have an additional middle layer, the MESODERM (gives rise to muscles and many internal organs) The Major Grades: 4 Dichotomies The Acoelomate, Acoelomate, Pseudocoelomate and Coelomate Grades In animals with a body cavity, the cavity may be completely lined by MESDERM, (a TRUE COELOMATE) or only partially lined (a PSEUDOCOELOM) The Major Grades: 4 Dichotomies The Major Grades: 4 Dichotomies The ProtostomeProtostome-Deuterostome Dichotomy The ProtostomeProtostome-Deuterostome DichotomyDichotomy- Cleavage PROTOSTOMES (mollusks, annelids, and arthropods) are distinguished from DEUTEROSTOMES (echinoderms and chordates) based on differences during development: A. Cleavage B. Coelom Formation C. Blastopore Fate 2 The Major Grades: 4 Dichotomies The Major Grades: 4 Dichotomies The ProtostomeProtostome-Deuterostome DichotomyDichotomy- Coelom Formation The ProtostomeProtostome-Deuterostome DichotomyDichotomy- Blastopore Fate PROTOSTOMES DEUTEROSTOMES Using Grades to Construct a Phylogenetic Tree of the Animal Kingdom PROTOSTOMES “first mouth” DUETEROSTOMES “second mouth Are Grades Clades?? Complicated by RAPID EVOLUTION of the animal phyla! An Arthropod fossil from the Burgess Shale; ©Natural History Museum London The Cambrian Explosion Possible Reasons for the Cambrian Explosion 1. EcologicalEcologicalpredatorpredator-prey relationships evolve Nearly all major animal body plans appear in Cambrian rocks dating 543543-525 mya. mya. Rapid emergence makes analyzing fossil record for evolution of groups difficult! 2. GeologicalGeologicalhigher concentration of O2 The Burgess Shale, British Columbia 3. GeneticGenetic- Variation in expression of Hox genes (“evo (“evo--devo”) devo”) 3 So Is a Grade a Clade? Molecular Evidence Sequencing SSUSSU-rRNA (and Hox genes) has provided additional evidence with which to construct Phylogenetic Trees Adding SSUSSU-rRNA to the Picture How does it look?? Resolving the Protostomes (Rearrangement #1) What happened to the Coelom? (Rearrangment #2) Acoelomates (flatworms) now with the Protostomes Rearrangement #3: Rearrangement #3: Emergence of the Ecdysozoa Emergence of the Lopho-trochozoa 4 Revised Version of the Cambrian Explosion? In Lab: A Survey of Animal Phyla 3 Major Groups of Bilateria Emerge: Lophotrochozoans Ecdysozoans Deuterostomes Sequence difference between these groups is large. Sequence difference within much more subtle! Can you make the grade?? 1. Radially Symmetrical, True Tissues 2. A Deuterostome ? ? How did you do?? 3. No True Tissues 4. A Protostome Ancestral Colonial Choanoflagellate One More Chance: Who’s who?? One More Chance: Who’s who?? 5 Looking More Closely at the Animal Kingdom One More Chance: Who’s who?? The Porifera (Parazoa) We’ll Start Here… The Porifera: Typical Anatomy Ancestral lineagelineage- no true tissues Lined with choanocyteschoanocytescreate currents, trap food Skeleton composed of spicules The Porifera: Sponge Sex Most sponges are hermaphrodites; eggs are retained in the mesophyl while sperm are released into the water. Fertilized zygotes develop into swimming larvae. Reproduction can also be asexual (fragmentation) 6 The Cnidarians Next Up: Radially symmetrical Diploblastic embryos (ectoderm and endoderm) Central digestive compartment (gastrovascular cavity) with single opening Can be either a polyp or medusa Stinging cells called cnidocytes contain capsules, the nematocyst, for snagging and poisoning prey The Cnidarians: Anatomy The Cnidarians: Anatomy The Cnidarians: Reproduction The Cnidarians: Anatomy (one example!) Cool Advances: • Simple nerve net to coordinate movement • Muscle-like contractile fibers (bundles of microfilaments) • Can sense light, gravity, and more 7 Cnidarian ‘Cousins’: The Ctenophora The Cnidarians: Diversity 1. Hydrozoa- mostly marine, polyp and medusa in most, polyp often colonial (a separate, radial phylum) • Morphologically similar, evolutionary relationship uncertain 2. Scyphozoa- marine, reduced polyp, large medusas • Two long retractable tentacles used in capturing prey 3. Anthozoa- marine, no medusa stage, sessile, mostly colonial • Use cilia for locomotion Worms and Beyond And Now For Something Completely Bilateral… The Platyhelminthes Acoelomates Earliest extensive organorgan-system development Nervous system with small “brain” Cephalization evident (eyespots!) Digestive track has single opening All remaining phyla are triploblastic, triploblastic, and are bilaterally symmetrical at some point in their life history The Diversity of Platyhelminthes The Flukes: Tapeworms: Why am I so flat??? Planaria: 8 The Nematodes (Roundworms) The Diversity of Platyhelminthes Digestive tract complete Pseudocoelom Ascaris: Trichinella: Vinegar Eels: The Annelids (Segmented worms) True Coelomates (+ all animals beyond) Annilids are schizocoelous Closed circulatory system Nervous system, oneone-way gut Earthworm Primarily freefree-living (Lumbricus): Leeches: The Development of the Coelom Planaria Ascarics Lumbricus Acoelomate Pseudocoelomate Eucoelomate The Molluscs General body plan includes the foot, the visceral mass, and mantle Open circulatory system with chambered heart The Arthropods Segmented body, covered by exoskeleton Typically divided into 3 tagmata: tagmata: the head, thorax, and abdomen Open circulatory system w/heart Reduced coelom WellWell-developed nervous system 9 The Echinodermata Leaving the Protostomes The Chordates Phylum includes sea squirts (tunicates), lampreys and hagfishes, fishes, amphibians, reptiles, birds and mammals Deuterostomes! Deuterostomes! 5-part body plan Water vascular system w/tube feet Bilateral larvae w/ “radial” adults Spiny skin, internal skeleton The Chordates 4 Common Features: 1. Flexible supporting skeletal rod called a notochord 2. Dorsal hollow nerve cord above the notochord 3. Pharyngeal pouches in the pharynx 4. Post anal tail The Chordates 10