BSC 116 BSC 116
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This 10 page Class Notes was uploaded by Ashley Bartolomeo on Sunday February 28, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Professor Harris in Spring 2016. Since its upload, it has received 26 views. For similar materials see Principles Biology II in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 02/28/16
Lecture 16: Lophotrochozoa, Ecdysozoa & Deuterostomia Overview Most animals belong to the Bilateria Molecular phylogenetics has revised our view of animal evolution o Lophotrochozoa o Ecdysozoa o Deuterostomia There is a wide variety of body plans among animals Major Animal Groups There are five major groups of animal phyla o Porifera: sponges; no true tissues, no symmetry o Cnidaria: jellyfish, sea anemones, coral; diploblastic, radial symmetry o Lophotrochozoa: flatworms, mollusks, segmented worms; triploblastic, bilateral symmetry o Ecdysozoa: arthropods, nematodes; triploblastic, bilateral symmetry o Deuterostomia: echinoderms, chordates; triploblastic, bilateral symmetry Most Animals Belong to the Bilateria Recognized based on several traits o Bilateral symmetry: have a head, etc. o Triploblastic: mesoderm for muscles, etc. o Most are coelomates: hydrostatic skeletons Around since before the Cambrian Explosion: 575 My Three main groups of phyla o Lophotrochozoa o Ecdysozoa o Deuterostomia Lophotrochozoa is One Group of Bilaterians 18 phyla grouped by molecular phylogenetics Some taxa have ciliated trochophore type larvae o Phylum Platyhelminthes: flatworms o Phylum Annelida: segmented-worms o Phylum Mollusca: mollusks Some have a feeding structure called a lophophore o Phylum Ectoprocta: bryozoans o Phylum Brachiopoda: lamp shells Many phyla lacking either o Phylum Rotifera: rotifers (“wheel animals”) Protist-crowned “Crown of cilia” used to capture food Many taxa: no males, asexual only Platyhelminthes is Represented By Free-Living & Parasitic Flatworms Flatworms generally long and flat acoelomates o Mainly parasitic Like cnidarians, lack through-gut: gastrovascular cavity o Serves for circulation Unlike cnidarians, have organs to maintain osmotic balance: protonephridia with cells called flame bulbs Most hermaphrodites: simultaneously male & female o Also capable of asexual reproduction There are Four Classes of Flatworms Class Turbellaria: Planarians o Mostly free-living Classes Monogenea & Trematoda: flukes o Parasites on or in other animals o Parasitic life cycles often complex: multiple hosts E.g., Schistosoma mansoni, blood fluke Class Cestoda: tapeworms o Intestinal parasites o No gastrovascular cavity, protonephridia, etc.; just gonads Annelida are Segmented Coelomate Worms Long & cylindrical coelomates o Coelomic spaces divided by septa o Body made of repeating segments Organs repeated in each segment Have a through-gut: mouth and anus Circulatory system Some hermaphrodites, some gonochoristic (separate sexes) Three classes o Class Polychaeta Mostly marine, also freshwater Have lateral parapodia for locomotion Many chaetae (“hairs”) o Class Oligochaeta: e.g., earthworms Mostly terrestrial and freshwater Few chaetae o Class Hirudinea: leeches Mostly freshwater Predators and blood parasites Mollusks Include Such Diverse Taxa as Clams, Snails, & Octopuses Phylum Mollusca has 8 classes, including: o Class Polyplacophora: chitons o Class Gastropoda: snails, slugs o Class Bivalvia: clams, mussels, oysters o Class Cephalopoda: squid, octopus, nautilus Many traits are shared among mollusks, but few are found in all taxa o Calcium carbonate shell (exoskeleton; except in octopus) Secreted by dorsal epidermis: mantle o Radula for feeding (except in bivalves) o Foot for crawling (chitons, snails), burrowing (bivalves), or swimming (octopuses) o Organs concentrated into visceral mass (not stretched over whole body, like worms) o Mantle cavity: space under mantle, behind visceral mass Houses gills, openings of gut, gonads, excretory system o Gonochoristic: separate sexes (exceptions in most classes) Lophophorates Have Long Been Grouped Together but They Were Deuterostomes Plathyhelminthes, annelids, and mollusks: some species have trochophore larvae o Inherited from bilaterian ancestor Other phyla in lophotrochozoa have lophophore: for suspension feeding o Phylum Ectoprocta: bryozoans (“moss animals”) Tiny, colonial; mostly marine o Phylum Brachiopoda: lamp shells Convergent morphology with bivalves Lophophorates have indeterminate, radial cleavage; blastopore becomes anus o Traditionally grouped with the other deuterostomes Ecdysozoa is Another Bilaterian Group Discovered by Molecular Phylogenetics Ecdysozoa is a newer grouping of 8 phyla o Discovered recently based upon DNA o All taxa molt their outer covering (go thru ecdysis) Includes two very diverse phyla o Phylum Arthropoda: over 1,000,000 species known E.g., insects, spiders, crabs Also extinct lineages; around since Cambrian Explosion o Phylum Nematoda: 25,000 known, but many times that waiting to be discovered (unsegmented) round worms Arthropods are Covered by a Jointed Exoskeleton Arthropods covered by a cuticle: non-living organic layer (protein, chitin) over epidermis o Thick in some places: rigid, hardened with calcium carbonate o Thin and flexible in other places o Provides points for muscle attachment: exoskeleton Arthropods are segmented like annelids o Each segment has a pair of appendages o Appendages diversified for variety of functions Sensory, feeding, locomotion Hard, waterproof exoskeleton facilitated the invasion of land 428 My Exoskeleton creates a few challenges o Need specialized structures for gas exchange Gills in aquatic taxa; terrestrial have pores leading to branching ducts (trachea or book lungs) o Needs to be molted (ecdysis) so animal can grow Generally gonochoristic (separate sexes) Arthropods are Represented by Four Extant Subphyla Subphylum Trilobitimorpha o Extinct; Paleozoic trilobites Subphylum Cheliceriformes o Arachnids: spiders, ticks, mites, scorpions o Horseshoe crabs Subphylum Myriapoda o Centipedes & millipedes Subphylum Crustacea o Decapods: lobsters, crabs, shrimp, krill o Isopods: pill bugs/ rollie-pollies o Copepods: tiny, planktonic o Barnacles Subphylum Hexapoda o Insects Most Species on Earth are Insects Crustaceans dominant in ocean, but insects everywhere else o >1,000,000 species divided among >30 orders Arose on land at least 416 My o Early evolution: fed on gymnosperms, etc. o 90 My diversified with angiosperms Wings are not appendages: extensions of dorsal cuticle o Originally served for thermoregulation? Gliding? Some insects tremendously helpful o They pollinate our crops Others are less helpful o They eat our crops: costs billions of dollars per year o Spread diseases: e.g., malaria, sleeping sickness (protists spread by mosquitoes, tsetse flies) Nematodes are Tiny but Diverse Round Worms Long and cylindrical but unsegmented o Pseudocoelomates Best known species parasites or agricultural pests o E.g., Trichinella Spiralis in undercooked pork o E.g., Necator Americanus, American hookworm Know much less about all the free-living species o Except for Caenorhabditis elegans: important model organism Vertebrates and Certain Invertebrates Are United in the Deuterostomia Traditionally, Deuterostomia included all the taxa with deuterostome development o Echinoderms, chordates, and lophophorates Modern Deuterostomia has two phyla: o Phylum Echinodermata Starfish, sea urchins, sand dollars, etc. o Phylum Chordata Vertebrates (fish, frogs, chickens, apes) and related invertebrates Echinoderms Have Secondary “Radial” Symmetry Phylum Echinodermata: “spiny skin” o “Penta-Radial” symmetry; biradial larvae o unique water vascular system with tube feet o No organs for water balance: exclusively marine o Asexual (regeneration) & sexual (broadcast spawning) reproduction Six classes: o Class Asteroidea: sea stars o Class Ophiuroidea: brittle stars o Class Echinoidea: sea urchins & sand dollars o Class Crinoidea: sea lilies & feather stars o Class Holothruoidea: sea cucumbers o Class Concentricycloidea: sea daisies Probably just weird asteroids Lecture 17: Early Branches of the Vertebrate Phylogeny Overview Phylum Chordata o Diagnostic traits o Invertebrate and vertebrate groups Sequences of evolutionary novelties allows us to reconstruct history of vertebrates o Fishes thru amniotes Major Animal Groups There are five major groups of animal phyla o Deuterostomia: echinoderms, chordates; triploblastic, bilateral symmetry All Chordates Share Four Unique Traits (at least at some point) Notochord: long flexible rod of cells o Provides skeletal support o Something for muscles to pull against for swimming o May be replaced by other skeletal elements Hollow, dorsal nerve cord o Otherwise, usually solid and ventral Pharyngeal slits o Pharynx: posterior to mouth o Water enters mouth passes thru slits: suspension feeding o In more derived chordates, modified into gills, jaws, etc. Post-anal tail o Muscular tail extends past anus There are 3 Chordate Clade that Lack Vertebrae Lancets (Cephalochordata) o Small suspension feeder capable of swimming o Adults live partially buried Turnicates (Urochordata) o Difficult to see how adult turnicates are chordates (missing most traits); present in larvae o Sedentary suspension feeder: basket-like pharynx with mucus that traps food Hagfishes (myxini): members of the Craniata, the clade to which we belong Among Vertebrates There Have Been a Number of Important Innovations A sequence of traits evolved that allow us to trace the evolution of vertebrates o Vertebrates; jaws; mineralized skeleton; lungs/ swim bladders; lobed fins/ appendages; legs; amniotic eggs; milk Each trait diagnoses a major taxon of interest There are 2 Clades of Jawless Vertebrates: The Cyclostomes 1. Hagfishes (Myxini): o No jaws, suck up worms and dead fish o Cartilaginous skull o Reduced vertebrae o Slime as defense against predators o Marine 2. Modern Lampreys (petromyzontida) still jawless, but with a rasping tongue o No jaws, rasping tongue o Larvae look a lot like lancelets o Cartilaginous Vertebrae o Most parasitic o Marine and freshwater Early Vertebrate Evolution Cartilaginous vertebrae and skull o Provided more skeletal support and spinal cord protection Other innovations o Mineralized teeth and armor plates Eventually led to mineralization of skeleton o Dorsal & ventral fins Led to more fins/ appendages o Semi-circular ear canals for balance Earliest fossil vertebrates date to 500 mya Conondants lacked jaws, internal skeleton composed of cartilage, mineralized dental hooks Jawless armored vertebrates o Armored with mineralized bone (predator protection?) no lateral fins Gnathostomes: Vertebrates with Jaws Jaws evolved from skeletal supports between gill slits o Gnathostomes since 450 My: e.g., placoderms (extinct) Other innovations o Skeleton ossified with hard matrix of calcium phosphate (bones) o Increase in forebrain size o Lateral line system: aquatic species sense vibrations in water (“hear”) Two extant clades o Chondrichthyes: sharks and rays Unmineralized skeletons (i.e., reduced to mostly cartilage) Buoyancy by storing oil in its liver: still denser than water o Osteichthyes: “bony fish” Retain mineralized skeletons Buoyancy using lungs/ swim bladders Osteichthyans: Gnathostomes with Lungs Lungs: allow osteichthyans to breath air o Modified into swim-bladder in most fish: gases move into/ out blood to control buoyancy Other innovations o Body covered with flattened bony scales o Glands secrete slime to reduce drag with water o Water drawn thru gills by muscular contractions Two extant clades o Actinopterygii: ray-finned fishes o Sarcopterygii: lobe-finned fishes (and tetrapods) Sarcopterygians: Osteichthyans with 4 Appendages Lobe-fins: pectoral and pelvic fins with rod-shaped bones surrounded by muscles o Axial limbs: provide support for “walking” in the shallows Three extant clades o Actinistia: coelacanths (latimera) Thought to have been extinct for 75 My until 1938 o Dipnoi: lungfishes Freshwater in South America, Africa and Australia o Tetrapods: “four legs” Amphibians, reptiles (including birds), & mammals Tetrapods: Sarcopterygians with Legs Sarcopterygians evolved legs to provide support and locomotion on land o Accumulation of features over 10s My o E.g., Acanthostega had limbs, but too weak to leave water for long; GILLS Lots of fossils demonstrate the transition of sarcopterygians to land Hard to draw a line at what is and isn’t a fish Amphibians Represent the Oldest Tetrapod Lineage Three orders of amphibians o Order Urodela: salamanders; “tailed” o Order Anura: frogs and toads; “no tail” o Order Apoda: caecilians; “no legs” Amphibious: lives on land and in water o Some amphibians fully aquatic, others fully terrestrial o Often aquatic larval stage (tadpole), metamorphosis to terrestrial adult o Eggs dry out quickly: must be wet or at least moist External fertilization Amniotes: Tetrapods with Water-Proof Eggs Amniotic egg: major innovation that got tetrapods fully on to land o Egg has four membranes (including the amnion) + a shell o Able to survive away from water (analogous to a seed) Two extant clades: o “Reptiles” (includes birds) o Mammals (includes humans) Lecture 18: Amniotes & the Evolution of Terrestrial Vertebrates – Part 1 Overview Evolution of the amniotic egg allowed exploitation of terrestrial environments o Two major clades: reptiles (+ birds) & synapsids (mammals) Modern reptiles (except birds) retain many ancestral amniote characteristics o Dominant terrestrial vertebrates during the Mesozoic: dinosaurs Amniotes: Tetrapods with Water-Proof Eggs Amniotic egg: major innovation that got tetrapods fully on to land o Egg has four membranes (including the amnion) + a shell o Able to survive away from water (analogous to a seed) Two extant clades: o “Reptiles” (includes birds) o Mammals (includes humans) A Key Adaptation to Terrestrial Life was the Amniotic Egg Amniotic egg: four extraembryonic membranes o Amnion: holds embryo in fluid Buffers against drying and shock o Chorion: gas exchange o Yolk sac: nutrient storage o Allantois: creates compartment for waste o Plus albumen: “egg white” o Plus a shell: hard or leathery Amniotes have egg that protects embryo away from water o Reptiles (+ birds) still lay eggs externally o But most mammals have lost their shell; raise embryo in uterus Amniotes developed other terrestrial adaptations o Skin less permeable to water/ gas o Use ribs (rather than throat) to breath “Reptiles” are Really a Paraphyletic Group What is a “reptile”? o Arose around 320 My o Things like tuataras, lizards, snakes, turtles & crocodiles o Body with hard, keratin scales: protection o Generally oviparous: lay shelled eggs on land Internal fertilization Some species viviparous: embryo retained in mother (no shell) o Ectothermic: body heated by environment Vs. endothermic: use higher metabolism to generate heat o Birds and mammals evolved from reptile ancestors Reptilian characters ancestral rather than derived “Reptiles” recognized by what they are not: non-bird, non- mammal amniotes This “reptiles” clade = Sauropsida Tuataras, Lizards & Snakes (Lepidosaurs); Turtles are Something Else Three extant lineages of Lepdiosaurs o Tuataras: 2 species on islands around New Zealand o Squamates= lizards + snakes (7900 species) Komodo dragons (varanids): legged snakes Also other legless lizards, not snakes: have eyelids, external ears, long tail Turtles have been hard to place o Easy to recognize: external shell About 300 species o Either considered to be sister to Archosaurs o Or, sister to Diapsids Extant Archosaurs are Represented by Two Clades: Crocs & Birds Crocodilians = crocodiles + alligators (23 species) o Tend to be aquatic Birds (Aves) siste to crocs o From 230-65 My: represented by dinosaurs Two major lineages of dinosaurs: o Ornithischian: “bird-hipped” o Saurischian: “lizard-hipped” Birds belong to this group Birds Evolved from Saurischian Theropods Around 150 My Theropods: things like T. rex Some species had feathers: keratin, like scales o Light weight for insulation, coloration o Feathers evolved much before flight Archaeopteryx: first bird, 150 My o Airfoil wings and long tail: capable of flight o Retained some dinosaur characteristics: e.g. teeth, clawed forelimbs, long tail Modern Birds (Class Aves) are Well Adapted for Flight Around 10,000 species of modern birds Many modifications for flight o No bladder, small gonads, air-filled bones: reduce weight o Endothermic: high metabolism to power flight o Keen vision o Fine muscle control o Brain large than other “reptiles” with similar body size Several modern flightless bird taxa o Ratites: ostrich, emu, rhea, etc. o Penguins; as well as some ducks, etc.
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