BIOL 112 1st Edition Lec-ture 13 Outline of Last Lecture I. Chloroplasts: A Second EndosymbiosisII. Modern ProtistansIII. Traditional GroupingsIV.General Eukaryotic Life CycleV. TermsVI.Domain EukaryaVII. Supergroup ExcavataVIII. AlveolataIX.ApicomplexansX. StamenopilaXI.OomycotaXII. Supergroup ArchaeplastidaXIII. AnimalsXIV. Body Plan Criteria for Organizing AnimalsXV. Digestive SystemOutline of Current LectureXVI. Phylogenetic TreesXVII. Early Animal EvolutionXVIII. Vendian Animal FossilsXIX. “The Cambrian Explosion”XX. What happened?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.XXI. Hox Gene ClustersXXII. Patterning GenesXXIII. Phylum ChordataXXIV. Disagreement of SchemesCurrent LectureI. Phylogenetic Trees•Suggested evolutionary patterns, depending on the sources of information used to construct the criteria for the branch points•Body plan (morphology) and development (embryology)-based scheme•Molecular sequence-based scheme•Schemes produced are different in some details•Agreement of Schemes•All animals have a common ancestor•Sponges are barely multicellular -- extremely primitive animals•Eumetazoa (all animals except sponges) have true tissues•Most animals are Bilateral (bilateral symmetry)•Vertebrates and a few other phyla belong to the deuterostomes•Most invertebrates belong to the protostomesII. Early Animal Evolution•How did we get animals?•Have to use molecular data to figure this out•First eukaryotic-like fossils ~2x10^9 years ago (Proterozoic)•Possible animal ancestors are choanoflagellates•protists that resemble cells of sponges•Earliest animal-like forms, 640x10^6 years ago (Ediacaran)III. Vendian Animal Fossils•635 x 10^6 -- 551 x 10^6 years ago•Includes the Ediacaran formations from Australia, but similar age fossil beds were found in China and the North Sea region•Fossils are very difficult to interpret•What kinds of animals? Unusual morphologies•Body plans? Bilateral symmetry not obviously apparent. Organs? Appendages?•Any descendants in modern times?•Fossils uncommon: all soft bodied•Some recognizable as cnidarians and perhaps ctenophores. Most are unlike any mod-ern forms•Some are quite large: up to 2 meters long•Many Vendian animals have a "quilted" appearance -- multiple thin extensions con-nected along a central axis•Others seem to have lived on a stalk and might have had triple symmetry, like Charniodiscus•All disappear about 551 x 10^6 years ago. Geological evidence of a planet-wide ice agethen -- environmental catastrophe that would cause extinctionsIV.“The Cambrian Explosion”•Beginning about 550 x 10^6 years ago, appearance of most modern animal phyla over 10x10^6 year period•Pre-Cambrian animal fossils are difficult to interpret in modern terms•Ediacaran Period (680x10^6 - 550x10^6) animal fossils are flattened and without shellsor skeletons•At Cambrian Explosion, fossil animals become common because we now see shells and skeletons; things more easily preserved•Transition to Cambrian Forms•It appears that most Vendian animals became extinct and left no modern descen-dants.•Cambrian forms more modern in appearance: distinct A/P and d/v axes, and with "hard parts": shells•But what was transition from primitive body plan (radially symmetrical) to bilateralsymmetry? What lineage? What genes involved?V. What happened?•Animal phyla have developed ability to make shells and skeletons•Cephalization; bilateral symmetry•Predator-prey arms race (armor)•Increasing O2 in atmosphere made higher metabolisms (bigger bodies) possible•Development of effective circulatory/gas exchange systems so that a thicker body is possible•Molecular basis: animals evolved regulatory gene combinations (Homeobox (Hox) Cluster on one arm of chromosome - distinguishing feature of being an animal) to build basic animal body plan (bilateral symmetry; A/P and d/v axes with limbs; cephal-ization) in larval and adult forms•Ancestral Bilateral•General agreement that common ancestor to modern bilaterian phyla is most likely something like a flatworm•Has bilateral symmetry: A/P and d/v axes•Bilateral symmetry implies cephalization — development of a head (brain, cluster of sensory organs) on anterior•Three tissue layers formed by gastrulation•But how get from more primitive phyla (sponges, cnidarians, etc.) to the flatworm form?•Compare existing pre-bilaterian forms to existing bilaterians to assess what might have happened to genetics•Analysis of What Happened•Fossils are limited•Can examine existing pre-lateral phyla (basal taxa) for possible ancestral genetic content relative to axes formation and embryologyVI.Hox Gene ClustersCommon patterns of expression in evolutionarily diverse organismsSignificance to formation of A/P axis in embryo: homeobox cluster genes pattern out the embryo structures from anterior to posterior. Pattern of genes on chromosome re-flects A/P pattern of expression of genes in embryoVII. Patterning Genes•A/P Genes -- Homeobox and Related Genes•Critical feature in K. Animalia is Hox Cluster•Regulatory genes: control expression of other genes•Expression of the genes on the chromosome is related to spatial expression in the embryo•d/v Genes -- Dpp/Sog; Chrd/Bmp4•Expression defines dorsal and ventral sides of embryo•Dpp/Sog defines d/v in flies; Chrd/Bmp4 defines d/v in vertebrates•Do basal groups have these genes? Are they expressed in similar patterns in embryos?•Embryology•The way the embryo develops is critical to how body plan develops in animal•Gastrulation •Folds embryo into 3 dimensions •Begins formation of the digestive system•Develops two or three layers of tissues in embryo (germ layers)•Location and control of gastrulation critical to developmentVIII. Phylum Chordata•Vertebrates are sub-phylum within this phylum•Very old: early chordates seen in Burgess Shale•Distinguishing Characteristics of this Phylum:•Presence of a notochord at some time in life cycle•Dorsal, hollow nerve cord (nervous system - spinal cord)•Presence of pharyngeal slits at some time in development•Presence of post-anal tailIX.Disagreement of Schemes•Mostly in the bilateral groups•Morphology/Development-based scheme divides bilaterians into two groups:•Deuterostomes: Chordates and Echinoderms•Protostomes: Arthropods,