Origin and Diversification of Animals PDF

Origin and Diversification of animals 1. Origin and evolution of animal body plans: Characteristic features of Animal body plans including the axis of symmetry, phylogenetic relationships among animals, Body Cavity, Segmentation, Cephalization, Germ layers. (3) 2. Invertebrates: o Origin...

Origin and Diversification of animals 1. Origin and evolution of animal body plans: Characteristic features of Animal body plans including the axis of symmetry, phylogenetic relationships among animals, Body Cavity, Segmentation, Cephalization, Germ layers. (3) 2. Invertebrates: o Origin and evolution of different major organ systems. Sponges, Cnidarians, Lophotrochozoans, Ecdysozoans, Echinoderms and Hemichordates. (3) 3. Vertebrates: o Origin and evolution of different major organ systems, Tetrapods, Amniotes, Mammals and Humans. (3) 4. Animal Nutrition: o Essential Nutrients, Stages of food processing - Ingestion, Digestion, Absorption and Assimilation of food. (2) o A brief introduction to the diversity in Invertebrate and vertebrate digestive systems. (2) 5. Circulation and Gas exchange: o Integration of respiratory and circulatory systems in animals, respiratory pigments. (1) o Different kinds of respiratory systems: Gills, Trachea, Vertebrate lungs, including air sacs in birds. (2) o Vertebrate circulation: Blood and circulation; anatomy of heart, ECG, cardiac cycle, regulation of cardiac output and blood pressure, transport of gasses in blood, regulation of body pH. (2) 6. Osmoregulation and Excretion: (4) o Osmoregulation, osmoregulators and osmoconformers o Obligatory exchanges of ions and water o Osmoregulation in water and terrestrial environment o Human excretory system as a model: Glomerular filtration, Tubular re-absorption and secretion, counter current mechanism, hormonal regulations. 7. Nervous System, Sensory and Motor Mechanisms: (5) o Neuron structure and functions, Genesis of membrane potential and action potential, conduction of action potentials, Sodium-potassium pump, calcium pump, Transmission at synapse, Neurotransmitters. o Eye-retinal components and photo-receptors. o Ear-cochlea, basilar membrane. Vertebrate skeletal muscle, other types of muscles, o Energetics of muscle contraction, sequence of events in contraction & relaxation. 8. Endocrine system: Brief introduction to hormones and their role as chemical coordinator. Vertebrate neuro-endocrine system. (3) 9. Hormones and Reproduction: o Different modes of reproduction: Asexual and sexual reproduction, parthenogenesis. (1) o Mammalian reproduction as a model of sexual reproduction: Male and female reproductive physiology, fertilization, pregnancy and childbirth. AIDS, contraceptives - as special topics. (3) What Characteristics distinguish the animals? Multicellularity. In contrast to the Bacteria, Archaea, and most protists, all animals are multicellular. Animal life cycles feature complex patterns of development from a single-celled zygote into a multicellular adult. What Characteristics distinguish the animals? Heterotrophic metabolism. All animals are heterotrophs. Animals are able to synthesize very few organic molecules from inorganic chemicals, so they must take in nutrients from their environment (either through their own actions, or in some cases with the aid of symbiotic species). What Characteristics distinguish the animals? Internal digestion. Most animals ingest food into an internal gut that is continuous with the outside environment and in which digestion takes place. What Characteristics distinguish the animals? Movement. In contrast to the majority of plants and fungi, most animals can move. Animals must move to find food or bring food to them. Muscle tissue is unique to animals, and many animal body plans are specialized for movement. How do we know Animals are Monophyletic Some animals do not move, at least during certain life stages, and some plants and fungi do have limited movement. Some animals lack a gut. Many multicellular organisms are not animals. So what is the evidence that groups all animals together in a single clade? Animal monophyly is supported by gene sequences and morphology The most convincing evidence that all the organisms considered to be animals share a common ancestor comes from phylogenetic analyses of their gene sequences. surprisingly few morphological features are shared across all species of animals Unique types of junctions between their cells (tight junctions, desmosomes, and gap junctions A common set of extracellular matrix molecules, including collagen and proteoglycans surprisingly few morphological features are shared across all species of animals Although some animals in a few groups lack one or another of these characteristics, it is believed that these traits were possessed by the ancestor of all animals and subsequently lost in those groups Common ancestor of animals was probably a colonial flagellated protist similar to existing colonial choanoflagellates which certain cells in the colony began to be specialized—some for movement, others for nutrition, others for reproduction, and so on Once this functional specialization had begun, cells could have continued to differentiate Common ancestor of animals Coordination among groups of cells could have improved by means of specific regulatory and signaling molecules that guided differentiation and migration of cells in developing embryos. Such coordinated groups of cells eventually evolved into the larger and more complex organisms that we call animals. A few basic developmental patterns differentiate major animal groups Differences in patterns of embryonic development have until recently provided many of the most important clues to animal phylogeny Analyses of gene sequences, however, are now showing that some developmental patterns are more evolutionarily variable than previously thought. A few basic developmental patterns differentiate major animal groups The first few cell divisions of a zygote are known as cleavage (Radial and Spiral). In general, the number of cells in the embryo doubles with each cleavage. Several different cleavage patterns exist among animals. In the protostomes (Greek, “mouth first”), the mouth arises from the blastopore, and the anus forms later. In the deuterostomes (“mouth second”), the blastopore becomes the anus, and the mouth forms later.  The process of gastrulation, which occurs during early embryonic development, involves the formation and migration of these germ layers. The three germ layers are initially formed during gastrulation, and they eventually give rise to all the specialized cells and tissues in the developing embryo. Gastrulation is a crucial and highly coordinated process in the early development of animal embryos, during which a single-layered blastula (a hollow ball of cells) is transformed into a multilayered structure with the formation of three primary germ layers: the ectoderm, mesoderm, and endoderm. Gastrulation is a fundamental step in embryonic development and sets the stage for the formation of different tissues, organs, and body structures. A few basic developmental patterns differentiate major animal groups Distinct layers of cells form during the early development of most animals. These cell layers differentiate into specific organs and organ systems as development continues. The embryos of diploblastic animals have two cell layers: an outer ectoderm and an inner endoderm. Embryos of triploblastic animals have, in addition to ectoderm and endoderm, a third distinct cell layer, mesoderm, between the ectoderm and the endoderm. The existence of three cell layers in embryos is a synapomorphy of triploblastic animals, whereas the diploblastic animals (placozoans, ctenophores, and cnidarians) exhibit the ancestral condition. Some biologists consider sponges to be diploblastic, but since they do not have clearly differentiated tissue types or embryonic cell layers, the term is not usually applied to them.  Germ layers are distinct layers of cells that form during the early stages of embryonic development in animals. These layers give rise to different tissues and organs in the developing organism. In many animals, including humans, there are typically three primary germ layers: the ectoderm, mesoderm, and endoderm. These germ layers are responsible for the development of the various structures and systems in the adult organism. Ectoderm: The ectoderm is the outermost germ layer. It gives rise to structures such as the skin, hair, nails, and the nervous system (including the brain and spinal cord). Specialized regions of the ectoderm also form sensory organs like the eyes and ears. Mesoderm: The mesoderm is the middle germ layer. It is responsible for the development of many internal structures, including muscle, bone, the circulatory system, and the excretory system (e.g., kidneys). The mesoderm also gives rise to the notochord, which plays a crucial role in early vertebrate development. Endoderm: The endoderm is the innermost germ layer. It forms the lining of the digestive and respiratory tracts, as well as various organs like the liver, pancreas, and the inner lining of the lungs. The endoderm is essential for the development of the body's digestive and respiratory systems.  Sponges, which belong to the phylum Porifera, are among the simplest multicellular animals, and they lack true germ layers. Unlike more complex animals, such as vertebrates, sponges do not exhibit the distinct three germ layers (ectoderm, mesoderm, and endoderm) that are characteristic of bilateral symmetry and advanced embryonic development. Instead, sponges have a relatively simple body structure, with two primary cell layers: Pinacoderm (Outer Layer): The pinacoderm is the outermost layer of cells and covers the exterior surface of the sponge. It is composed of flattened epithelial-like cells that serve a protective function. Choanoderm (Inner Layer): The choanoderm is the inner layer of cells that lines the internal cavities of the sponge. These cells, known as choanocytes, have flagella and collar-like structures and are involved in filter-feeding and generating water flow through the sponge. Animal Body Plans The general structure of an animal, the arrangement of its organ systems, and the integrated functioning of its parts are referred to as its body plan. Although animal body plans vary tremendously, they can be seen as variations on four key features: The symmetry of the body The structure of the body cavity The segmentation of the body External appendages that are used for sensing, chewing, locomotion, mating, and other functions Most animals are symmetrical The overall shape of an animal can be described by its symmetry. An animal is said to be symmetrical if it can be divided along at least one plane into similar halves. Animals that have no plane of symmetry are said to be asymmetrical. Placozoans and many sponges are asymmetrical, but most other animals have some kind of symmetry, which is governed by the expression of regulatory genes during development. Sponges are loosely organized animals Sponges are the simplest animals. Although they have some specialized cells, they have no distinct embryonic cell layers and no true organs. Early naturalists thought sponges were plants because they were sessile and lacked body symmetry. Placozoans placozoans are structurally very simple animals with only a few distinct cell types. Individuals in the mature, asymmetrical life stage are usually observed adhering to surfaces (such as the glass of aquariums, where they were first discovered, or to rocks and other hard substrates in nature). Their structural simplicity—they have no mouth, gut, or nervous system—initially led biologists to suspect they might be the sister group of all other animals. Ctenophores are radially symmetrical and diploblastic Ctenophores, also known as comb jellies, lack most of the Hox genes found in all other eumetazoans. Ctenophores have a radially symmetrical, diploblastic body plan. The two cell layers are separated by an inert, gelatinous extracellular matrix called mesoglea. Ctenophores have a complete gut: food enters through a mouth, and wastes are eliminated through two anal pores. Cnidarians are specialized carnivores Cnidarians have epithelial cells with muscle fibers whose contractions enable the animals to move, as well as simple nerve nets that integrate their body activities. They also have specialized structural molecules (collagen, actin, and myosin). They are specialized carnivores, using the toxin in their nematocysts to capture relatively large and complex prey (see Figure 31.9). Some cnidarians, including many corals and anemones, gainadditional nutrition from photosynthetic endosymbionts that live in their tissues. Cnidarians, like ctenophores, are largely made up of inert mesoglea