Topic 12 The Evolution of Animals I - Biology Past Paper

Topic 12 The evolution of animals I Learning Outcomes List and define characteristics that are shared by all animals Demonstrate how genetic data can help determine the position of animals within the phylogeny Identify various modes of asexual reproduction in animals Justify the be...

Topic 12 The evolution of animals I Learning Outcomes List and define characteristics that are shared by all animals Demonstrate how genetic data can help determine the position of animals within the phylogeny Identify various modes of asexual reproduction in animals Justify the benefits of bilateral symmetry Explain how homeotic genes can affect the resemblance between different animal body plans Define key words in animal embryogenesis and development Associate each embryonic tissues with the organs they form Illustrate differences between the development of protostomes and deuterostomes Calculate, compare and explain the consequences of different surface-to-volume ratios Define the different modes of thermoregulations Determine the modes of thermoregulation based on graphical data Explain and provide examples of adaptations in response to physical/physiological problems that animals face on land 2 https://www.wooclap.com/BIO1130 3  Topic 12 The evolution of animals I 12.1 – Characteristics of animals Animals First direct evidence. (560 Mya). Multicellular soft- bodied eukaryote. Molecules of cholesterol (only produced by animals). 5 What is an animal? Eukaryotes Multicellular Heterotroph (organic source of carbon to produce its own organic molecules) … with a few exceptions: Elysia chlorotica (sap sucking slug) à steal chloroplasts (kleptoplast) from algae but these are not transmitted to the next generation. Some photosynthesis proteins genes have been transferred to the slug’s genome! ~ 1.5M species 6 What is an animal? Eukaryotes Multicellular Heterotroph (organic source of carbon to produce its own organic molecules) … with a few exceptions: Elysia chlorotica (sap sucking slug) à steal chloroplasts (kleptoplast) from algae but these are not transmitted to the next generation. Some photosynthesis proteins genes have been transferred to the slug’s genome! Breathe oxygen (aerobic/oxidative respiration) ~ 1.5M species 7 What is an animal? Able to move Able to reproduce sexually (or both sexually and asexually) Cells organized into tissues (integrated group of cells with a common structure, function, or both.) Development goes through the blastula stage Absence of cell wall à extracellular matrix with interconnected proteins (e.g. collagen) to maintain cohesion and structural support. 8 Multicellularity: a key step Multicellularity requires the evolution cell adherence (attachment) and cell signaling (communication). Similarities between unicellular choanoflagellates and multicellular animals à Comparative analyses of genome sequences. Zebrafish Cadherins: proteins involved in cell-to-cell attachment Sponge (Oscarella carmela) …but animal cadherins also contain a highly conserved region not found in the choanoflagellates… à the cytoplasmic cadherin domain (CCD) Nichols et al 2012 à Transition to multicellularity in animals involved new ways of using proteins or parts of pre-existing proteins 9 Tissues and cell specialization Sponges have… …choanocytes that resemble choanoflagellates (feeding by filtration) …amoebocytes that transport nutrients to other cells and can differentiate into any other cell. 10 Tissues and cell specialization Sponges (porifera) do not have true tissues à cells are not connected together and are not separated from other tissues by membranous layers Sponges have… …choanocytes that resemble choanoflagellates (feeding by filtration) Sponges also do not have neurons …amoebocytes that transport nutrients to other cells and can differentiate into any This isother cell. in contrast with Eumetazoa Protostomia 11 Reproduction Life cycle is dominated by the diploid phase (multicellular, more complex individual): diplontic life cycle. The two haploid gametes (non-motile egg and flagellated sperm) are produced by meiosis and do not undergo mitosis: unicellular haploid phase. Sperm cell (Drosophila bifurca) 12 Reproduction All animals reproduce sexually, but some can also reproduce asexually: Budding in jellyfish 13 Reproduction All animals reproduce sexually, but some can also reproduce asexually: Fragmentation in sponges and flatworms (planaria) à Presence of neoblasts: undifferentiated stem cells that can regenerate an entire organism 14 Reproduction All animals reproduce sexually, but some can also reproduce asexually: Parthenogenesis: asexual reproduction in which females produce offspring from unfertilized eggs. Zebra shark New Mexico whiptail Stegostoma fasciatum Aspidoscelis neomexicanus 15  Topic 12 The evolution of animals I 12.2 – Body plans, embryogenesis and development Body plans Radial symmetry: Central axis No anterior or posterior region Bilateral symmetry: Dorsal and ventral sides Anterior region (mouth and sensory organs) Posterior region (tail, anus, feeding, locomotion) 17 Body plans Genes that control animal development are similar across a broad range of taxa. Hox genes play important roles in the development of animal embryos à control the expression of >100 other genes determining the morphology Hox genes are homeotic genes: regulatory genes that control the placement/spatial organization of body parts by controlling the developmental fate of groups of cells. à identity of tissues, orientation, segmentation, repetitions… The colour code indicates the parts of the embryos in which these genes are expressed and the adult body regions that result. 18 Body plans Some animals do not develop directly into adults à at least one larval stage with a very different morphology. Larva: sexually immature form of an animal that is morphologically distinct from the adult à usually eats different food, and lives in a different habitat than the adult (less competition) Metamorphosis: developmental transformation that turns the animal into a juvenile that resembles an adult but is not yet sexually mature. 19 Embryogenesis and development Diploid zygote undergoes mitosis (without cell growth) à blastula 8-cells stage, cell divisions can undergo either… Spiral cleavage: oblique to the axis of the body. Radial cleavage: parallel to the axis of the body. Determinate cleavage: each cell defines a specific part of the embryo. Indeterminate cleavage: each cell has the potential to produce a complete embryo. yer t i o n : f rom 1 la la Gastru ayer structure Gastrulation (formation of a gastrula through infolding) to multil à Formation of embryonic tissues that will develop into adult body parts 20 Embryogenesis and development The archenteron represents the primitive gut (= external environment) The blastopore corresponds to the Blastopore develops into: opening of the archenteron the mouth (protostomes = “mouth 1st”) or… the anus in (deuterostomes = “mouth 2nd”) 21 Embryogenesis and development The archenteron represents the primitive gut (= external environment) The blastopore corresponds to the Blastopore develops into: opening of the archenteron the mouth (protostomes = “mouth 1st”) or… the anus in (deuterostomes = “mouth 2nd”) 22 Embryogenesis and development Animals with radial symmetry show two embryonic tissues only: Ectoderm Diploblastic (coral, jellyfish, cnidaria…) Endoderm Animals with bilateral symmetry show three embryonic tissues: Ectoderm Mesoderm Triploblastic (worms, insects, vertebrates…) Endoderm These embryonic tissues (germ layers) form the specific tissues and organs of the body. 23 Coelom and organs in the mesoderm The coelom corresponds to the cavity lined by tissues derived from the mesoderm between the digestive track (derived from the endoderm) and the outer body layer (derived from the ectoderm) Functions of body cavities: Structural support of the body (skeleton and hydrostatic skeleton) Transport and diffusion system (nutrients, gas exchanges, waste elimination…) Allow the growth of organs and their independent movements Some triploblastic animals lost the coelom (acoelomates) Organs are suspended in the coelom and become more specialized: More efficient digestion (digestive track) Increased production and storage of gametes (gonads) 24 Embryogenesis and development The infolding of the neural plate (from the ectoderm) forms the neural tube and many structures of the nervous and sensory system The notochord is a dorsal, longitudinal and flexible rod (from the mesoderm) along the anterior-posterior axis of a chordates à Gives structural support (the spine in vertebrates) 25 Embryogenesis and development The infolding of the neural plate (from the ectoderm) forms the neural tube and many structures of the nervous and sensory system The notochord is a dorsal, longitudinal and flexible rod (from the mesoderm) along the anterior-posterior axis of a chordates à Gives structural support (the spine in vertebrates) 26  Topic 12 The evolution of animals I 12.3 – Challenges and adaptations Many physical and chemical challenges Animals must deal with variations in temperature, humidity, solute concentration, gas partial pressure, resource availability, etc. Different groups often show similar Thermoregulation Respiration Osmoregulation morphological adaptations to similar environments (convergence). Communication and Reproduction Sensory mechanisms treatment of information 28 Surface-to-volume ratio Surface-to-volume ratio: surface/volume = m2/m3 Influences: heat conservation metabolic activity exchanges (nutrients, gases) As the size of the organism increases the surface-to-volume ratio decreases: à the surface area is proportionally smaller for larger organisms à heat loss is decreased for larger organisms 29 Thermoregulation Homeostasis: The steady-state physiological condition of the body Thermoregulation: mechanism for maintaining body temperature in a range that is compatible with life (ex: enzymatic activity) If the source of heat is internal (metabolism) à endotherm If the source of heat is external (sunlight) à ectotherm If there is a mechanism to attenuate the variations of the internal environment when the external environment fluctuates à homeotherm (regulator) If the variations in the internal environment can be tolerated when the external environment fluctuates à poikilotherm (conformer) Ectotherms/endotherms refer to the heat source! Homeotherms/poikilotherms refer to the constancy of the internal temperature! 30 Osmoregulation Extreme heat, dry conditions or variations in solute concentration (for aquatic animals) can affect the animal’s water loss. Adaptations to regulate water loss: Presence of ionocytes that retain Na+ (therefore water) in high salinity Presence of sweat glands for evaporation and cooling Presence of kidneys that concentrate the urine Production of uric acid (guano) to avoid water loss 31