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1 Evolution of Animals Introduction to Animal Diversity Lecture 7 Winter 2014 Eukaryotes Prokaryotes Major differences Prokaryotes • No nucleus 2 Eukaryotes • Nucleus – Nucleoid region – (DNA in a membrane-bound region) • Simple • No membrane bound organelles • Complex • Membrane bound organelles • Smaller (1-5 nm) • Evolutionarily older • Larger (10-100 nm) • Evolutionarily younger – Organelle – a structure with a specified function w/i a cell The Origin of Eukaryotic Cells 3 Evolution of the endomembrane system • Remember endomembrane system? See Fig. 25.9 4 Endosymbiosis Remember endosymbiosis? Mitochondria • Formed when early anaerobic eukaryotic cell engulfed an aerobic bacterium • Benefits? Plastids • Formed when early eukaryotic cell (w/mitochondria) engulfed a photosynthetic cyanobacterium • Benefits? Protist Diversity 5 What is a protist? • Eukaryote • Unicellular (primarily) – Colonial – Multicellular (algae “seaweed”) • Metabolically diverse – Photoautotrophs – Heterotrophs – Mixotrophs – combine both See Fig. 25.9 1 6 Protist Diversity Origin of Multicellular Organisms 7 • Earliest multicellular fossil ~1.2 bya • Cells gather in colonies • Cell specialization occurs to divide particular life functions • Multicellularity evolved several times independently among eukaryotes • “Protista” is a paraphyletic grouping Fig. 28.3 8 What are animals? • • • • • • Eukaryotes Multicellular Heterotrophic Sexual reproduction (most) Embryonic stage – blastula & gastrula Specialized cells, tissues, organs for capturing food, avoiding predation – Muscles, nerves, sensory organs 9 Brief Animal History • Common ancestor of living animals ~675-875 mya ??? Fig. 32.3 10 Brief Animal History Animal Phylogeny 11 • 565-550 mya - First fossils • 535-525 mya - Cambrian explosion – Large diversification of animals – A Wonderful Life by Stephen Jay Gould • 360 mya - Vertebrates move to land Fig. 32.5 Fig. 32.10 2 Body Symmetry 12 13 Body Symmetry • Asymmetric (no true symmetry) Bilateral symmetry • A body form with a central longitudinal plane that divides the body into two equal but opposite halves – e.g., sponges • Radial symmetry – Can be divided into equal but opposite halves by any plane through its central axis – Sessile or planktonic Fig. 32.7 – Must cut on midline • Cephalization – Sensory organs concentrated in anterior region • Benefits? Fig. 32.7 Evolution of true body tissue 14 15 Embryonic Development • Blastula Tissue: • An integrated group of cells with a common function, structure, or both – Hollow ball of cells that marks the end of the cleavage stage • Gastrulation – Blastula folds inward, producing layers of embryonic tissue – Separated by membranous layer • Gastrula • Sponges lack true tissues • All other animals - embryo with layered tissue – Stage encompassing the formation of the layers • Germ layers – Ectoderm – Endoderm – Mesoderm Fig. 32.2 16 Evolution of digestive cavity Evolution of true body tissue • Diploblasts – Ectoderm & endoderm • E.g., Cnidarians (jellies, corals) • Triploblasts – Ectoderm, mesoderm, endoderm – Bilateral symmetry – Mesoderm forms muscles & most organs between digestive tract and outer covering Digestive cavity • Gastrovascular cavity – Sac with single opening – Acts as both mouth & anus Fig. 33.5 17 • Complete digestive tract (alimentary canal) – Two openings, a mouth and an anus Fig. 41.9 3 Evolution of body cavity 18 Body cavity (coelom) • Fluid or air-filled space separating the digestive tract from the outer body wall • Functions: 19 Evolution of body cavities • Pseudocoelom – Formed from mesoderm & endoderm tissue – Pseudocoelomates – Cushions internal organs – Organs can move independently of outer body wall • No body cavity – Acoelomates • True coelom – Formed from mesoderm tissue – Coelomates Fig. 32.8 Fig. 32.8 Segmentation & Tagmatization 20 • Segmentation Skeletal Systems 21 Endoskeleton • Hard supporting element buried within the soft tissue • E.g., bones & cartilage (mammals), skeletal fibers of inorganic material or proteins (sponges), ossicles (sea stars) – Divided into parts, sections • Tagmatization – Groups of segments become specialized to form specific function for whole body • Tagmata (tagma, sing.) Fig. 33.29 Skeletal Systems 22 Animal Development 23 Fig. 33.36 Exoskeleton • Hard encasement deposited on an animal’s surface • E.g., shells (snails, clams), cuticle (crabs, insects) • Metamorphosis – A dramatic change from the larval form to the adult form of an animal • Larva – Sexually immature form of an animal that is morphologically distinct from the adult 4 Protostome Vs. Deuterostome Development 24 Protostome Vs. Deuterostome Development 25 Coelom formation Cleavage – Gastrula stage • Spiral • Protostome – Cleavage planes diagonal to vertical axis of embryo • Radial – Coelom forms from splits in the mesoderm (schizocoelous) – Cleavage planes parallel or perpendicular to vertical axis of embryo • Deuterostome • Tiers of cells aligned directly above the other – Coelom forms from mesodermal outpocketing in archenteron • Determinate – Developmental fate of cells determined very early • Indeterminate – Each cell retains capacity to develop a complete embryo Fig. 32.9 Protostome Vs. Deuterostome Development Fig. 32.9 26 Animal Phylogeny 27 Fate of blastopore • Blastopore – Indentation that during gastrulation leads to the formation of the archenteron • Protostome = “first mouth” • Deuterostome = “second mouth” Fig. 32.9 Fig. 32.10 5