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This 8 page Class Notes was uploaded by Amalia Cristiano on Saturday March 7, 2015. The Class Notes belongs to 24010 at San Diego State University taught by Berta in Spring2015. Since its upload, it has received 33 views. For similar materials see Biology 204 in Biology at San Diego State University.
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Date Created: 03/07/15
Biology 204 Section 2 Animals are multicellular heterotrophic eukaryotes that ingest food items with tissues that develop from embryonic germ cell layers Comparing amp Contrasting Multicellular Eukaryotes Plants most are photoautotrophs deriving energy from light inorganic food source Fungi chemoheterotrophs like animals deriving energy from organic compounds but use absorptive nutrition Animals ingestive chemoheterotrophs Animals are multiceluar but our closest relatives choano agelates are unicellular Choano agellates small 10 micrometers aquatic collared agellates Evidence for Relationship to Animals Their cells are very similar to collarcells choanocytes of sponges Unicellular but cells often live as colonies where they show 1 some cellular specialization different cell types have different functions in the colony 2 Shared parts of genome include proteins for cell signaling cell adhesion previously thought to be restricted to animals Uniting characteristics in the genome gt DNAbased phylogeny indicates close relationship 3 Molecular Phylogeny based on 50 important genes Uniting Feature 1 Animal cells posses an extracellular matrix Important Functions of the ECM holds cells together in tissues adds structural support acts as a lter involved in cell communication gt cell communication amp coordination very important in multicellular organisms Uniting Feature 2 10005 of shared genomic changes unique to animals Uniting Feature 3 All metazoans possess HOX genes highlyconserved developmental regulatory genes more soon General Characteristics of Animal Life There are 35 major animal groups phya with distinctive body plans Body Plan a description of the overall system of body organization includes symmetry tissue complexity appendages segmentation etc Only One group the Chordates includes Vertebrate animals The remaining 34 groups comprise INVERTEBRATE animals Of the 13 million described animal species ALL BUT 50000 are invertebrates Invertebrate animals vary tremendously in form function amp ecology Animal Life began in the Oceans the majority of the major animal groups remain marine 2 animal groups have invaded and are particularly successfuon Land gt Arthropods amp Vertebrates Ediacaran Fauna First discovered in rocks from Namibia and Newfoundland this assemblage of softbodied organisms was named for a locality in the Ediacaran Hills of South Australia and these have now been recovered from more than 30 localities around the world The earliest fossils are the simple discs seen above from the Twitya formation in the Mackenzie Mountains Canada Dating to about the same time are trace fossils geoogical records of biological activity which seem to be faecal strings yes poop This is important since it suggests that a complete gut with an anus was present in these bilaterians Sponges are known to have evolved by this time FossHs The Doushantuo Formation 580570Ma in southern China preserve in exquisite 3D detail early metazoan embryos and a host of algae These embryos have undergone several cleavages indicating the presence of differentiated cell lines and fairly complex development Until today these embryos represent the oldest known metazoan body fossils What do these fossil embryos communicate to us That mitosis is a process that is at least 570 Mya That at least a few homeotic genes were in place and building these early animalsThat these embryos are probably of cnidarians or bilaterians In short the Ediacaran period of more than 100 million years was an early experiment in building complex animals and these for the most part were replaced with true metazoans after a major extinction event Beginning of a Cambrian World Fossils from the Burgess shale The Burgess shale fossils were rst discovered in 1909 by Charles Walcott right secretary of the Smithsonian Institution Named after the Burgess Shale rock formation Mount Burgess in the Canadian Rockies Over 65000 specimens found Since then more of the very same fossils have been found in widely dispersed areas such as China Greenland Siberia Australia Europe and the USA The Burgess Shale site 510 Million years ago This drawing depicts one reconstruction of the Burgess Shale site and its surroundings as they were long ago We can identify nearby underwater locations that today have become mountains about two miles high Wapta Dennis and Stephen It is easy to imagine how an avalanche of ne mud sliding down from the submerged reef top would have carried off any animals living in the shallow reef waters above This avalanche could have caught some animals in midwater and would have overwhelmed and buried any creatures living at its base The hard parts of all these animals caught in the mudslide were preserved as fossils like the process at any other Cambrian site However here the fine mud also penetrated and lled all available spaces within the animals thus preserving the shapes and locations of all the soft parts Major Point of Diversi cation around 530 MYA where fossils representing 12 present animal groups appear suddenly gt Cambrian Explosion much diversification in body plans over a very short geologic time span Explaining the Cambrian Explosion Multiple interacting factors Diversification in HOX gene cluster gt major genomic changes causing major morphological changes Increased atmospheric oxygen gt increased metabolic rates larger body sizes Escalation of predatory prey relationships development of more complex foodwebs Molecular phylogeny with timescale based on molecular clock alone chronogram De ning Animals Metazoa Animal Relatives choano agellates et a1 Metazoan Apomorphies General Characteristics body plans species diversity deep history etc Molecular systematics Comparing nucleic acids or other molecules to deduce relatedness Allows us to understand phylogenetic relationships that can t be inferred using comparative anatomy Ex Can we even compare humans and fungi morphologically Mol Syst allows us to understand evolutionary relationships at the species level and far above phyla kingdoms domains The more recently two species have branched from a common ancestor the more similar their DNA sequences should be The longer two species have been on separate evolutionary paths the more their DNA should have diverged What gene do we study Different genes evolve at different rates DNA coding for conservative sequences like ribosomal RNA genes is useful for investigating relationships between taxa that diverged hundreds of millions of years ago This comparison has shown that animals are more closely related to fungi than to plants mtDNA evolves rapidly and has been used to study the relationships between different groups of Native Americans who have diverged since they crossed the Bering Land Bridge 13000 years ago An organism s evolutionary history is documented in its genome Gene duplication a process that increases the number of genes in the genome provides more opportunities for evolutionary change These duplications result in gene families groups of related genes within an individual s genome Two types of homologous genes Orthologous and paralogous genes Homologous genes have been found in organisms separated by huge evolutionary distances At least 60 of human disease genes and 50 of ALL human genes have homologs in fruit ies Gene duplication has increased the number of genes in many genomes The number of genes has not increased at the same rate as the complexity of organisms Humans have only four times as many genes as yeast Molecular clocks help track evolutionary time Some regions of the genome appear to accumulate changes at constant rates Molecular clocks can be calibrated in real time by graphing the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record Molecular clocks are used to estimate dates of divergences without a good fossil record For example a molecular clock has been used to estimate the date that HIV jumped from apes to humans Sponges phylum Porifera gt relatively earlydiverging animal lineage Some molecular phylogenies show that Sponges include multiple EarlyDiverging groups gt monophyly still disputed Class Demospongiae skeletons typically made of collagen or spongin protein Demosponges comprise 90 of sponge species Class Calcarea skeletons of calcium carbonate spicules Class Hexactinellida Sponges glass sponges skeletons made of fused silica spicules typically live at great depths in oceans Evidence for Early Divergence Cellular Grade of Organization Sponges lack true embryological germ cell layers amp lack adult tissue layers More cell individuality than cells in remaining animals some cells mobile and cell differentiation is reversible impressive powers of regeneration intact sponge entirely disassociated new sponges can form General Characteristics of Sponges Always aquatic mostly marine 8000 described species Fossil record earlier than Cambrian glass sponges particularly wellrepresented Lack organized body symmetry they are asymmetrical Sessile ie attached amp mostly immobile filterfeeders pass food particles past a capturing organ Sponges dominate in benthic marine habitats Generic Sponge Bodv loose assemblage of cells suspended in gelatinous matrix mesohyl supported by a skeleton of spicules calcium carbonate silica andor protein collagen spongin Fundamental processes shared bv all animals gain nutrients respiration 02 in C02 out rid body of metabolic wastes exchange gametes gt sponges conduct these processes by pumping water through porous body Anatomy of a sponge Porocytes cells surrounding pore openings Amoebocytes food transport structural support e g producing spicules Choanocytes collar cells create water currents and trap microscopic food particles gametes also involved in egg amp sperm production Water is drawn through the pores into a central cavity the spongocoel and then ows out through a larger opening called the osculum No true tissues in sponges but they do have different cell types choanocytes amoeobocytes and porocytes among others Body is made of two layers of cells separated by a gelatinous region called the mesohyl Since both layers are in direct contact with water gas exchange and waste removal occurs via diffusion across the cell membrane The morphological and genetic similarities between choanocytes and the cells of choano agellates supports that animals evolved from a choano agellatelike ancestor Sponge reproduction Most sponges are hermaphroditic every individual functions as both male and female by producing both sperm and eggs Eggs reside in the mesohyl and the sperm are ejected from the choanocytes or amoebocytes into the water current Cross fertilization results from sperm being drawn into neighboring individuals and the eggs are fertilized in the mesohyl The zygotes then develop into agellated swimming larvae that disperse from the parent sponge Larva settles on a suitable surface and develops into a sessile adult How do sessile sponges protect themselves or prevent fouling 1 with glass or calcite spicules II produce various bioactive compounds often in association with symbiotic bacteria Compounds with anticancer antifungal antiin ammatory properties gt important drugs from the sea Oldest Living Animals are Glass Sponges Sponges living in Antarctic waters cold foodpoor have very low metabolic rates measured by oxygen consumption grow to be very OLD estimates up to 10000 years old and very large e g up to 2 meters tall Recall that many Invertebrate groups are poorlyknown gt Sponge species diversity is also poorlyknown 8000 known gt 15000 estimated Modern researchers using rapidlyevolving DNA sequences to better understand true species diversity Use of RapidlyEvolving Sequences for Species Identi cation DNA Barcoding compare sequence of the gene of interest to preexisting catalog All remaining animals Eumetazoa with true tissues derived from embryonic germ cell layers EGCLS liploblastic Eumetazoa Cnidaria jellies corals relatives With two EGCLs ectoderm amp endoderm gt ultimately give rise to specific adult tissues Ectoderm gt forms adult epidermis Endoderm gt forms adult gastrodermis Radial Symmetry Single Oral mouth aboral furthest from mouth body axis Multiple planes resulting in equivalent halves contrast with bilateral symmetry condition Generalities about Cnidw most display radial symmetry Gastrovascular Cavity extends throughout body gt functions as simple transport system for exchange of food items gases wastes Possess nerve cells Because they capture foodrespond to stimuli from all sides the nervous system is diffuse gt nerve net Have specialized cells cnidog es fundamental to their predatory lifestyle most cnidocytes house stinging organelles called nematocysts Single oral opening leads to blind gut gt Gastrovascular Cavity GV cavity sometimes greatly subdivided eg extends into tentacles all cells of body in contact With GV uids or external medium
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