Chapter 32 An Overview of Animal Diversity Objectives From Powerpoint 1 Know the major groups of animals and what an animal is 2 Know major characteristics for divisions of animals and the possible origins of modern phyla 3 Know the different feeding movement and sensory strategies of animals Know characteristics of non bilateral phyla 32 1 ANIMALS ARE MULTICELLULAR HETEROTROPHIC EUKARYOTES WITH TISSUES THAT DEVELOP EMBRYONIC LAYERS NUTRITIONAL MODE Animals differ from both plants in fungi in their mode of nutrition by ingesting living or nonliving organic material and using enzymes to ingest it They do not produce organic molecules in photosynthesis like plants and they do not grow on food or feed on absorption like fungi CELL STRUCTURE AND SPECIALIZATION Animals are eukaryotic and multicellular Unlike plants they lack the structural support of a cell wall Instead proteins external to the cell membrane such as collagen provide structural support The cells of most animals are grouped similarly into functional units called tissues Muscle tissue and nerve tissue are an example and are vital to animal lifestyle REPRODUCTION AND DEVELOPMENT Most animals reproduce sexually and the diploid stage usually dominates the life cycle The sperm and egg haploid stage are produced by meiotic division which does not happen in plants and fungi A flagellated sperm fertilizes a larger non motile egg forming a diploid zygote The zygote undergoes successful mitotic divisions called cleavage and forms a blastula hollow ball Gastrulation occurs where layers of embryonic tissues that will develop into adult body parts are produced Tis stage is called a gastrula Although some animals directly develop into adults most animals have at least 1 larval stage A LARVA is a sexually immature form of an animal that is distinct from the adult A larva will undergo metamorphosis and turn into a juvenile that resembles the adult but is not sexually mature Although morphology varies between all animals genes that control development are similar for all animals These developmental genes regulate the expression of other genes and contain sets of DNA called homeoboxes MOST ANIMALS SHARE A UNIQUE HOMEOBOX CONTAINING FAMAILY OF GENES CALLED HOX GENES Sponges lack hox genes but have other homeobox genes Hox genes arose via duplication of earlier homeobox genes and underwent further duplications 32 2 THE HISTORY OF ANIMALS SPANS MORE THAN HALF A BILLION YEARS STEPS IN THE ORIGIN OF MULTICELLULAR ANIMALS One way to gather information on the origin of animals is to identify the protist groups most closely related to animals Molecular and morphological evidence has placed the CHOANOFLAGELLETES as the closet relatives of animals Scientists exploring how animals may have arisen from single celled ancestors noted that cells must evolve to attach and signal to each other An experiment revealed that Choanoflagellate Monosiga Brevicollis shared 78 protein domains key structural or functional regions of a protein that only occur in animals M Brevicollis has certain genes that encode domains of proteins of how animal cells attach to one another CADHERINS as well as genes that encode proteins for Cell Signaling pathways DNA sequence evidence show animal cadherin proteins are composed primarily of the domains also found in Chonanoflagellates However animals also had CCD domains not found in Chonanoflagellates which suggests that the cadherin attached protein was rearranged and the CCD domain was incorporated later NEOPROTEROZOIC ERA 1 BILLION 542 MILLION YEARS AGO The first generally accepted fossils of macroscopic animals are from 560 MYA and are believed to belong to the EDICARIAN BIOTA soft bodied multicellular eukaryotes In addition some of these fossils are though to be mollusks snails and their relatives while others may be related to sponges and cnidarians The fossil record from the EDIACARAN PERIOD provides evidence of predation and increasing animal diversity a trend that continued in the Paleozoic PALEOZOIC ERA 542 251 MILLION YEARS AGO Another wave of animal divarication occurred during the CAMBRIAN PERIOD known as the CAMBRIAN EXPLOSION which ultimately led to more animal phyla Fossils for arthropods chordates and echinoderms were found in strata from the Cambrian Era These fossils which include the first large animals with hard mineralized skeletons which look very different from most living animals Most of the fossils from the Cambrian Explosion are of BILAERIANS members who have 2 sided or bilaterally symmetric forms and a complete digestive tract and efficient digestive tract The diversity of animal phyla increased during the Cambrian the diversity of Edicarian life forms declined One hypothesis for this is that natural selection which allowed for novel adaptions to emerge The second hypothesis is that Oxygen enabled larger animals and animals with higher metabolic rates to thrive A third hypothesis includes changes to genes affecting development such as the origin of Hox genes and the addition of new micro RNA s affect gene regulation which led to new genes These hypotheses are not exclusive and could have each played a role MESOZOIC ERA 251 65 5 MILLION YEARS AGO First coral reefs formed giving habitats to animals Some reptiles returned to water Origin of wings and flight mechanisms First mammals emerged tiny nocturnal insect eaters CENOZOIC ERA 65 5 MILLION YEARS AGO TO PRESENT Rise of large mammalian herbivores GLOBAL COOLING PRIMATES adapted to new environments 32 3 ANIMALS CAN BE CHARCTERIZED BY BODY PLANS A body plan is a particular set of morphological and developmental traits developed into a functional whole the living animal SYMMETRY A basic feature of animal bodies is their type of symmetry There are 2 types of symmetry RADIAL AND BILATERAL Radial symmetry includes a top and bottom but no right left and front and back BILATERAL SYMMETRY is 2 sided symmetry and has 2 axes of orientation front to back top to bottom These animals have dorsal top ventral bottom anterior front and posterior back Many organisms with bilateral symmetry have sensory equipment of the anterior end and a central nervous system brain in the head Symmetry usually fits lifestyle TISSUES Germ layers form the various tissues and organs of the body The ECTODERM the germ layer covering the surface of the embryo gives rise to the outer covering of the animal and in some animals the Central Nervous system The Endoderm forms the innermost germ