Introduction to Animal Diversity PDF

Introduction to Animal Diversity Ryan R. Williams, M.D., Ph.D. Biology 122 California State University Dominguez Hills Overview Animal evolution began in the ocean over 600 million years ago Over one million currently living species of animals have been identified...

Introduction to Animal Diversity Ryan R. Williams, M.D., Ph.D. Biology 122 California State University Dominguez Hills Overview Animal evolution began in the ocean over 600 million years ago Over one million currently living species of animals have been identified However, the number of extinct species is estimated to be between 3 and 30 million Animals vary in complexity—from sea sponges to crickets to chimpanzees Classification systems of animals are based on: Anatomy, evolutionary history, embryological development, and genetics New species are still being identified Figure 27.1 The leaf chameleon (Brookesia micra) was discovered in northern Madagascar in 2012. At just over one inch long, it is the smallest known chameleon. (credit: modification of work by Frank Glaw, et al., PLOS) This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. Overview Two different groups within the Domain Eukaryota have complex multicellular organisms: Plants and the animals Animals closest living relatives are the fungi While some fungi are multicellular, they do not have complex different tissues (unlike animals and plants) Animals all require a source of food and are therefore heterotrophic Ingesting other living or dead organisms May be carnivores, herbivores, omnivores, or parasites Versus fungi which are heterotrophs, but decomposers Versus plants which are autotrophs Figure 27.2 All animals that derive energy from food are heterotrophs. The (a) black bear is an omnivore, eating both plants and animals. The (b) heartworm Dirofilaria immitis is a parasite that derives energy from its hosts. It spends its larval stage in mosquitos and its adult stage infesting the hearts of dogs and other mammals, as shown here. (credit a: modification of work by USDA Forest Service; credit b: modification of work by Clyde Robinson) This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. Overview Due to the necessity to collect food most animals are motile, at least during certain life stages The typical life cycle in animals is diplontic The diploid state is multicellular and dominant The haploid state is gametic producing single celled sperm or egg Alternation of generations (mutiple body forms) characteristic of plants and fungi is not found in animals In animals who have multiple body forms throughout their life (e.g., butterflies), all body forms are diploid During development, animal embryos pass through a series of stages that establish a determined and fixed body plan For example, dogs always have four limbs versus oak trees with different numbers of branches Development recapitulates (follows) the major steps of evolution Overview Kingdom Animalia Eukaryotes Multicellular Diverse cell and tissue types Heterotrophs Obtain energy and organic molecules by ingesting other organisms Active movement Move more rapidly and in more complex ways Huge diversity of form and size Range in size from microscopic to enormous Animal Tissues Different types of tissues are responsible for carrying out specific functions Differentiation and specialization of tissues is part of what allows for such incredible animal diversity No cell walls Versus plants and fungi Cells may be embedded in an extracellular matrix Ex: bone cells reside within a matrix of calcium phosphate Unique intracellular communication Ex: gap junctions Channels between cells that allow for the passage of small molecules such as ions, glucose, and amino acids Animal Tissues Four major tissue categories Epithelial tissues – covers, lines, protect and secrete Connective tissues – cells embedded in an extracellular matrix (ex: bone, cartilage) Muscle tissue – for movement Nervous tissue – to sense the environment and coordinate movement Animal Tissues Epithelial tissues Cover and protect both external and internal body surfaces May also have secretory functions Ex: the epidermis of the integument Ex: the lining of the digestive tract and trachea Ex: the layers of cells that make up the ducts and glands Animal Tissues Many specialized tissues of animals are used for seeking and processing food Sensory structures help animals navigate their environment To detect food sources To avoid becoming a food source (for other animals!) Movement is driven by muscle tissue attached to supportive structures like bone or chitin Movement is coordinated by neural tissue The evolution of these tissues allows animals to rapidly sense and respond to their environment To survive and compete with other species and meet their nutritional demands Five Monophyletic Animal Clades Parazoa Placozoa (multicellular amoebae) Porifera (sponges) Placozoa and Parazoa do not have specialized tissues derived from germ layers of the embryo They do possess specialized cells Placozoa have only four cell types Parazoa have nearly two dozen cells types Eumetazoa 3. Cnidaria (jellyfish and their relatives) 4. Ctenophora (the comb jellies) 5. Bilateria (all other animals) All have specialized tissues derived from the germ layers of the embryo Animal Reproduction & Development Most use sexual reproduction Development involves a determined and fixed body plan Morphology determined by genetics Versus plants and fungi whose morphology influenced by the environment Some animals produce larval forms that are different from the adult Incomplete metamorphosis Ex: grasshoppers, the young resemble wingless adults, but gradually produce larger and larger wing buds during successive molts Complete metamorphosis The embryo develops into larval stages that may differ greatly in structure and function from the adult Regardless of the series of developmental stages the morphology of each stage is the same Fixed by genetics Figure 27.4 (a) The grasshopper undergoes incomplete metamorphosis. (b) The butterfly undergoes complete metamorphosis. (credit: S.E. Snodgrass, USDA) This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. Animal Reproduction and Development Most animal cells are diploid (2n) Somatic cells are diploid Gametes are haploid Most animals reproduce sexually Haploid egg and sperm unite (fertilization) → diploid zygote Distinguishes them from most fungi, most protists and all prokaryotes Animal Reproduction and Development Most animals reproduce sexually, but there are exceptions Several groups have an asexual phase of life cycle (Ex: cnidarians, flatworms) Social insect males often haploid Budding and fragmentation – hydra, sea anemones Haplodiploid sex-determination Males develop from unfertilized eggs and are haploid Referred to as parthenogenesis Females develop from fertilized eggs and are diploid Used by some vertebrates and insects Individuals are not required to find mates Has potential for buildup of deleterious mutations Animal Reproduction and Development Early development after zygote forms Cleavage (series of mitotic cell divisions) After three divisions → 8-cell stage Cells (blastomeres) continue to divide and/or rearrange Morula Solid ball of cells Blastocyst Migration of cells → creates a hollow ‘ball’ With an inner cell mass Blastocoel is internal cavity  (a) Cleavage of Blastomeres zygote, two-cell stage (day 1) Zona pellucida (b) Cleavage of Nucleus zygote, four-cell stage (day 2) Cytoplasm (c) Morula (day 4) (d) Blastocyst, external view (day 5) Inner cell mass (e)Blastocyst Blastocoele (coele=cavity) sectioned, internal view (day 5) © 2015 Pearson Education, Inc. Animal Reproduction and Development The inner cell mass consists of cells (stem cells) that develop into all the cells of the organism The inner cell mast differentiates into to the blastodisc with two layers Epiblast which becomes the ectoderm germ layer Hypoblast which become endoderm germ layer  FERTILIZATION ZYGOTE Fertilization produces a single cell, or zygote. Blastomeres Early Morula Late Morula Inner cell mass During cleavage, cell divisions produce a hollow ball of cells called a blastocyst. This process Blastocoel takes about a week to complete. Blastocyst The inner cell mass differentiates into the epiblast and the hypoblast. Epiblast Hypoblast © 2015 Pearson Education, Inc. Animal Reproduction and Development Invagination of the blastocyst forms a blastopore (opening) and archenteron (embryonic gut) Diploblastic animals Evolved first Have two germ layers Endoderm and ectoderm Triploblastic animals Evolved from diploblasts Undergo gastrulation Ectoderm cells migrate and form a third germ layer (mesoderm) Have three germ layers Endoderm, mesoderm and ectoderm Note: -blast refers to developmental tissue or stem cells Animal Reproduction and Development Gastrulation – forms the gastrula A major step in evolution Occurs in most animals (triplobasts) A third germ layer forms Cells from the epiblast move toward the center of the blastodisc creating a primitive streak Then, they begin to migrate between the epiblast and hypoblast layers This creates third distinct layer of cells, the middle germ layer (mesoderm)  Animal Reproduction and Development Embryonic disc at gastrulation: Ectoderm Yolk sac Mesoderm Endoderm (b) Transverse section of blastodisc during early stages of gastrulation, about 16 days after fertilization © 2015 Pearson Education, Inc. Animal Reproduction and Development The three layers of cells in triploblasts are: Ectoderm Derived from the epiblast layer Mesoderm New layer between the epiblast and hypoblast Derived from epiblast cells that migrated through the primitive streak Endoderm Derived from the hypoblast layer Animal Reproduction and Development The different germ layers are programmed to become a variety of specialized tissues that form the organs Endoderm gives rise to: Epithelial tissues Ex: Inner lining of digestive tract and respiratory tract Mesoderm gives rise to: Epithelial tissues Ex: inner lining of body cavities and blood vessels Connective tissues Bone, cartilage, blood, and other organs Muscle tissue Ectoderm gives rise to: Epithelial tissues Skin Neural tissue Animal Reproduction and Development Homeotic (HOX) genes “Master” regulatory genes that control development of all animals – code for transcription factors Determine body plan, segmentation, number and placement of appendages, embryonic polarity Homologous across animal kingdom Highly conserved in gene sequence & chromosome location Features Used to Classify Animals True tissues Symmetry Number of tissue layers Body plan and cavities Origin of mouth and anus Symmetry Asymmetrical Lack of symmetry (no axis) Porifera (sponges) Radial symmetry Arrangement around central axis…parts ‘radiate’ outward Suited for encountering environment from any direction Good for stationary or planktonic lifestyle Cnidarians and ctenophores Bilateral symmetry (all other animals) Divides body along sagittal plane into right & left halves May only be during development (echioderms) Allows for cephalization Collection of sense organs in head Suited for moving forward as predators or prey Symmetry Symmetry Animals are first classified based on tissues and symmetry Parazoa No true tissues or symmetry Phylum Placozoa Thin, flat, multicellular amoeba-like Phylum Porifera Sponges Eumetazoa (‘true’ animals) All other animals Have at least two of the four tissue categories Exhibit symmetry Radial Bilateral Figure 27.7a The (a) sponge is asymmetrical, and the (b) jellyfish and (c) anemone are radially symmetrical. (credit a: modification of work by Andrew Turner; credit b: modification of work by Robert Freiburger; credit c: modification of work by Samuel Chow) This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. FIGURE 27.8 The bilaterally symmetrical human body can be divided by several planes. This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. Classification of Animals Eumetazoa are then divided based on: Type of symmetry Number of germ layers present during development Radiata – diploblasts Two germ layers – ectoderm and endoderm Radial symmetry Cnidarians, ctenophores Bilaterata – triploblasts Three germ layers – ectoderm, mesoderm, endoderm Bilateral symmetry All other animals Figure 27.9 During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm. Triploblasts develop a third layer—the mesoderm—between the endoderm and ectoderm. This OpenStax ancillary resource is © Rice University under a CC-BY 4.0 International license; it may be reproduced or modified but must be attributed to OpenStax, Rice University and any changes must be noted. Any images credited to other sources are similarly available for reproduction, but must be attributed to their sources. Classification of Animals Triploblasts are classified based on the presence or absence of a coelom (body cavity) Coelom is derived from mesoderm Lies between body wall and visceral organs Organs can move within coelom Acoelomates – lack body cavity (tissue only) Platyhelminthes (flatworms) Pseudocoelomates – “False” body cavity Derived from both endoderm and mesoderm Still functional – hydrostatic skeleton (improves mobility) Nematodes (roundworms) Coelomates (“eucoelomates”) – true body cavity Body cavity & internal organs lined with mesoderm Connective tissues holds organs in place, allowing motion Most other animals Classification of Animals Classification of Animals Bilaterata are divided into two major clades Protostomes – further divided into two major clades Lophotrochozoa – either have a trochophore larva and/or lophophore (feeding structure) Ecdysozoa – molt their exoskeleton (ecdysis) Include Arthropoda and Nematoda Deuterostomes – include echinoderms & chordates Classification of Animals Triploblasts with bilaterally symmetric, and true coeloms (eucoelomates) also can be divided into groups based on: Cleavage patterns and the fate of the blastopore Protostomes Spiral cleavage – due to angled cleavage → spiral pattern of cells along embryo axis Determinate – fate of cells is determined very early Blastopore becomes mouth Deuterostomes Radial cleavage – cell division at right angles Indeterminate – fate of cells determined somewhat later in development Blastopore becomes anus Classification of Animals Classification of Animals ▪ Ectoderm ▪ Mesoderm ▪ Endoderm Classification of Animals For much of the history of science, animals were classified by morphological characters Can be misleading Similar structures may have different evolutionary histories Analogous structures may have evolved through convergence Characters may be lost Modern systematists (people who classify organisms) use biochemical, molecular and genetic evidence Classification of Animals Modern advances in our phylogenetic understanding of animals come from molecular analyses Classifications and phylogenies continue to change as more data are collected Molecular and genetic data include: Mitochondrial DNA Nuclear DNA Ribosomal RNA sequences Molecular technology will continue to make major contributions to the study evolutionary relationships Continuing to change our current view of evolution Pre-Cambrian Animal Life Precambrian time period is known as Ediacaran period (after certain fossils) 635–543 million years ago (mya) Ediacaran biota likely evolved from protists Cambrian ‘Explosion’ of Animal Life Cambrian period – 542–488 mya One of the most rapid periods in animal evolution → new phyla Cambrian ‘explosion’ Most of today’s phyla originated Echinoderms, mollusks, worms, arthropods, chordates Cambrian ‘Explosion’ of Animal Life Cause of Cambrian ‘explosion’ is debated Preceded by rising O2 levels and ocean calcium levels Presence of shallow seas allowing for ecological variation Changes in predator-prey relationships Genetic innovations Hox regulatory genes The percentage of oxygen in Earth’s atmosphere rose sharply Evidence exist for/against these around 300 million years ago. hypotheses and others… probably some combination Cambrian ‘Explosion’ of Animal Life Dramatic global and regional climate change can also lead to mass extinctions Changes in moisture and temperature Major losses of diversity Permian-Triassic boundary – greatest extinction event Likely due to impact event(s) from meteors and/or volcanic activity Post-Cambrian Evolution and Mass Extinctions There have been five mass extinction events (MSE) after the Cambrian period We may now be entering what appears to be the sixth MSE Previous MSEs are likely due to drastic climate change caused by asteroids and/or tectonic events, among other causes The potential current MSE appears to be human-related Current extinction rates have been estimated by some to be higher than previous MSEs, although over a geologically very short time span…stay tuned