Download Ch. 32 An Introduction to Animal Diversity

Ch. 32
An Introduction to Animal Diversity
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Essential Question:
How did the structure change in animals as they evolved?
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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)
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Early Embryonic Development
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Cleavage = a succession of mitotic cell divisions without cell growth between division cycles
gastrulation = layers of embryonic tissues that develop into adult body parts
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­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
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one hypothesis of origin of animals from flagellated protist
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Origins of animals
Animals evolved around late precambrian ­ Cambrian 565­525 million years ago
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Burgess Shale fossils
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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
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Animal Phylogenetic tree
characterized by animal body plans
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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
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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
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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
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­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
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cnidarians and ctenophores have two germ layers (ecto and endoderm) = diploblastic
bilateria are triploblastic = three germ layers
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Branch Point 3­ Acoelomate, Pseudocoleomate, coelomate
Acoelomate = have no body cavity between digestive tract and outer body wall
ex. Platyhelminthes (flat worms ­ Planaria)
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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
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Coelomate = have a true coelom, fluid filled body cavity from mesoderm tissue, have mesentaries
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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
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Branch 4 ­ Protostome­Deuterostome Among Coelomates
mouth forms from a 2nd opening
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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
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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
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Modern phylogenetic tree based on SSU­rRNa
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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
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or lophophore = crown of ciliated tentacles
Ecdysozoa = arthropods ­ shed exoskeleton
ecdysis= process of shedding exoskeleton
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Comparing the molecular based and grade based phylogenetic trees
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