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Ch. 32 An Introduction to Animal Diversity 1 Essential Question: How did the structure change in animals as they evolved? 2 Characteristics of animals: a. multicellular, heterotrophic eukaryotes b. no cell walls, structural proteins (collagen) hold cells together c. intercellular junctions tight junctions, desmosomes, gap junctions d. two types of cells only in animals nervous and muscle cells e. most reproduce sexually (diploid stage is dominant) sperm fertilizes egg zygote zygote cleavage blastula (hollow ball of cells) after blastula, get gastrulation (process of making a two cell "cup" shape = gastrula) 3 Early Embryonic Development 4 Cleavage = a succession of mitotic cell divisions without cell growth between division cycles gastrulation = layers of embryonic tissues that develop into adult body parts 5 some animals have larval stages (sexually immature stage) some undergo metamorphosis (stage that transforms animal into adult) f. Have Hox genes containing homeoboxes of DNA sequences genes that regulate expression of other genes # of Hox genes is related to complexity of anatomy believed to have evolved from colonial flagellated protist that lived 700 million years ago oldest animal fossils 575 million years ago 6 one hypothesis of origin of animals from flagellated protist 7 Origins of animals Animals evolved around late precambrian Cambrian 565525 million years ago 8 Burgess Shale fossils 9 Cambrian explosion burst of animal origins, diversification three hypotheses: 1.Ecological causes predatorprey relationships lead to adaptations of shells and locomotion 2. Geologic Causes enough oxygen in air to support animals 3. Genetic causes diversification associated with evolution of Hox genes, led to embryonic morphology differences 10 Animal Phylogenetic tree characterized by animal body plans 11 branches of phylogenetic are called grades = "a certain body plan features shared by animals belonging to that branch" branch point 1 = ParazoaEumetazoa Dichotomy parazoans = lack true tissues (sponges) eumetazoans = have true tissues http://sps.k12.ar.us/massengale/earthworm_dissection.htm http://www.seasky.org/reeflife/sea2a.html sponge earthworm 12 Branch point 2 RadiataBilateria Dichotomy radial symmetry (radiata) symmetry radiates from center has top and bottom, no head or rear, no left or right ex. cnidaria (jellyfish) Ctenophora (comb jellies) http://www.jellyfish.iup.edu/ most animals are sessile (attached to something) or plankton (free floating) comb jellies http://jellieszone.com/ctenophores.htm 13 bilateral symmetry = (two sided), has top(dorsal) and ventral (bottom), anterior and posterior, and left and right side animals with this are called bilateria includes most animals that move place to place 14 cephalization comes with bilateral symmetry, where sensory areas associated with anterior end have germ layers that form tissues and organs: ectoderm= surface of embryo, becomes outer covering of animal and in some, the central nervous system endoderm = innermost germ layer, becomes digestive tube mesoderm = middle layer, forms muscles and other organs between digestive tube and outer covering 15 cnidarians and ctenophores have two germ layers (ecto and endoderm) = diploblastic bilateria are triploblastic = three germ layers 16 Branch Point 3 Acoelomate, Pseudocoleomate, coelomate Acoelomate = have no body cavity between digestive tract and outer body wall ex. Platyhelminthes (flat worms Planaria) 17 Pseudocoelomate = have a body cavity, not lined by mesoderm derived tissue, uses both mesoderm and endoderm ex. Rotiferarotifers and Nematodaroundworms rotifer http://www.microscopyuk.net/mag/indexmag.html? http://www.microscopyuk.net/mag/wimsmall/rotidr.html 18 Coelomate = have a true coelom, fluid filled body cavity from mesoderm tissue, have mesentaries 19 functions of a body cavity 1. fluidfilled so helps prevent injuries of internal organs 2. hydrostatic skeleton for muscles to work 3. allows internal organs to grow and move without moving whole body ex. heart, lungs, digestive tract 20 Branch 4 ProtostomeDeuterostome Among Coelomates mouth forms from a 2nd opening 21 Protostomes 1. undergo spiral cleavage = diagonal planes of cell division 2. determinate cleavage = cleavage does not form a viable embryo 3. have schizocoelus development of coelom = coelom forms from splits in the mesoderm 4. blastopore [opening of archenteron (blind pouch)] forms mouth ex. mollusks, annelids, arthropods 22 Deuterostomes 1. radial cleavage = cleavage planes are parallel or perpendicular to vertical axis 2. Indeterminate cleavage = each cell can turn into a viable embryo 3. enterocoelous = coleom forms from mesodermal "outpocketing" archenteron 4. blastopore forms the anus ex. echinoderms, chordates 23 Modern phylogenetic tree based on SSUrRNa 24 difference between traditional and molecular based phylogenetic tree molecular has two clades in protosomes Lophotrochozoa and Ecdysozoa Lophotrochozoa = annelids and mollusks have trochophore larva trochophore larva 25 or lophophore = crown of ciliated tentacles Ecdysozoa = arthropods shed exoskeleton ecdysis= process of shedding exoskeleton 26 Comparing the molecular based and grade based phylogenetic trees 27 28