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Evolution Content • 1. An introduction • • • • • • to evolution 2. Historical view (the evolutionary thinking) 3. Genetic variation 4. Mechanisms: the processes of evolution 5. Microevolution vs Macroevolution 6. Speciation 7. Issues on evolution Evolution Evolution = Change. Biological Evolution = Change in the intrinsic qualities of life over time. NOT progressive change. What can change? Characteristics of species Number of species Evolution Microevolution = Change in the genetic qualities of populations within a species over time. Macroevolution = Change in the number of species and the formation of groups of species. Speciation = formation of species Results of Evolution • Anagenesis = change within a species lineage(number not increase) • Cladogenesis = change and diversification History: Early 1800’s Natural Theology Discover God’s plan, study nature. Essentialism = Organisms are imperfect reflections of perfect eternal “essences.” (invariant) Natural groups reflect the essential groups in the mind of God. History: Early 1800’s Paleontology = study of fossils. Fossil = preserved remnant of an organism that lived in the past Certain fossils only found in certain rock strata (layers). Some organisms are extinct! Earth = VERY OLD Sedimentary Rocks = layered rocks formed by settling particles. Sedimentary Rocks & Fossils youngest layer oldest layer Sedimentary Rocks & Fossils Dead Thing Sedimentary Rocks & Fossils Fossil (Dead Thing) Sedimentary Rocks & Fossils Fossil (Dead Thing) Sedimentary Rocks & Fossils EROSION Fossil (Dead Thing) Sedimentary Rocks & Fossils Fossil (Dead Thing) Sedimentary Rocks Geologic Time Scale Geologic scale based on the fossil record. (time divisions UNequal) Eras = four largest time periods (Precambrian --> Paleozoic --> Mesozoic --> Cenozoic) Periods subdivide eras. Mass Extinction = extinction of a large proportion of existing species. They separate many eras or periods. Geologic Time Scale Cenozoic Mesozoic extinction of dinosaurs first flowering plants first dinosaurs & mammals Paleozoic “fern” forests form coal first land plants & animals first vertebrates near present oxygen levels Precambrian Eons = hundreds of millions of years in duration(บรมยุค) Eras(มหายุค) Eons period(ยุค) epochs. Biostratigraphy: The organisation of sedimentary rocks into units on the basis of the fossils they contain Biostratigraphy: Charles Darwin Mid-1800’s, Charles Darwin Studied medicine & theology Traveled on H. M. S. Beagle Bred pigeons The Origin of Species, 1859 TWO big ideas Common Descent (old idea) Natural Selection (new idea) Natural Selection Mechanism of change within one species. (Proposed by Darwin.) Microevolutionary process. First evidence from plant and animal breeding by humans to create domestic forms. Natural Selection Populations can grow tremendously. In nature, populations remain stable in size due to limited resources (K). THEREFORE, there is a struggle to survive and reproduce within species. Organisms vary in inheritable characteristics (genetic). THEREFORE, reproduction varies based on differences in inherited traits. Natural Selection DEFINITION Differential reproduction (survival) based on differences in inherited characteristics. NOT “survival of the fittest” Population Population Population Population Population Population Population Fitness FITNESS = the relative contribution of an individual to the next generation More fit = more surviving offspring Less fit = fewer surviving offspring “Survival of the fittest” = circular, non biological statement แฟคเตอร์ที่มีอิทธิพลต่อ fitness Adaptation Adaptation = characteristic that results from natural selection also... a trait that enhances the reproductive success of the bearer. Not ALL characteristics of organisms are “adaptations.” Difficult to provide evidence that a characteristic is truly an adaptation. Laboratory Selection ลายจุดบนตัวปลาหางนกยูงส่ วนใหญ่ ถูก ควบคุมด้ วยพันธุกรรม ลายจุดนีช้ ่ วยใน การพรางตัวให้ เข้ ากับสิ่ งรอบข้ างเพื่อ ป้ องกันการถูกจับกินโดยปลาใหญ่ แต่ ลายจุดนีก้ ช็ ่ วยให้ ดูเด่ นกว่ าตัวที่ไม่ มลี าย จุด จึงดึงดูดคู่ผสมพันธุ์ Microevolution Sexual Selection “Special” Kinds of Selection Natural Selection = differential reproduction (survival) based on differences in inheritable characteristics (different alleles). Sexual Selection = natural selection based on mate choice. Artificial Selection = natural selection due to conscious human choice. (e.g., dogs, wheat) Sexual Selection Artificial Selection Artificial Selection p. 399 Population Genetics Population = localized group of individuals of the same species Population genetics = studies the genetic variation within populations Genotype = the genes (alleles) possessed by an organism Phenotype = the physical characteristics of an organism Genetics “Review” Genes (DNA) in cells direct cell activities. Most cells have TWO copies of every gene. (DIPLOID) One copy from each parent. Sperm or egg have ONE copy of every gene. (HAPLOID) Genetics “Review” Genetics “Review” The same gene can have different forms (Alleles). E.g., blue iris allele and brown iris allele of eye color gene Diploid individual with the same 2 alleles = homozygote. Diploid individual with 2 different alleles = heterozygote. Genetics Gene “A” has 2 alleles, “A” and “a.” AA or aa = homozygotes. Aa = heterozygotes. AA, Aa, and aa = genotypes. Calculation of allele frequencies. Population Genetics Gene pool = all the alleles in a population Genetic structure = frequencies (%) of alleles and genotypes in a population. Mendelian population = interbreeding group within a population. Hardy Weinberg Hardy-Weinberg Theorem = describes a population that is NOT evolving. p2 + 2pq + q2 = 1 p = frequency of A in the pop. q = frequency of a in the pop. p+q=1 Random mating P(A)=p P(a)=q P(A)=p P(a)=q AA=p2 Aa =pq aA=pq aa=q2 AA + 2Aa + aa = p2 + 2pq + q2 = 1 (p+q) 2 = 1 p+q = 1 Hardy Weinberg p2 + 2pq + q2 = 1 p2 = frequency of AA in the pop. 2pq = frequency of Aa in the pop. q2 = frequency of aa in the pop. Hardy-Weinberg p2 + 2pq + q2 = 1 The frequency of AA in a population at H.-W. equilibrium is 0.25. What is the frequency of Aa in this population? Hardy-Weinberg p2 + 2pq + q2 = 1 p2 = 0.25 p = 0.5 p+q=1 0.5 + q = 1 q = 0.5 Hardy-Weinberg p2 + 2pq + q2 = 1 p = 0.5 q = 0.5 2pq = frequency of Aa 2(0.5)(0.5) = frequency of Aa 0.5 = frequency of Aa Microevolutionary Processes Microevolution = small scale evolutionary changes. Natural Selection Non-random mating Genetic Drift Gene Flow (Migration) Mutation Mutation Mutation = introduction of random genetic variation. Source of new alleles. THE SOURCE of variation. Change in the DNA (in a sex cell). Relatively rare and random. Some chemicals can increase mutation rate (mutagens). ผลกระทบของมิวเทชัน • มิวเทชันอาจเกิดขึ้นที่ยนี ต่างๆที่ทาหน้าที่ควบคุม(regulatory genes) ซึ่งมีผลกระทบค่อนข้างรุ นแรง เพราะยีนที่ทาหน้าที่ควบคุม อาจมีอิทธิพลต่อยีนอื่นๆหลายยีน • มิวเทชันที่ยนี ควบคุมส่ วนใหญ่จึงทาให้ไซโกตตาย ตัวอย่างของ nonlethal regulatory mutations ที่เกิดกับ HOX genes ในมนุษย์ซ่ ึงอาจก่อเป็ นผลให้เกิดลักษณะ polydactyly ซึ่งหากให้ผลดีกจ็ ะกระจายไปในประชากร Gene Flow Gene flow = Gaining alleles from or losing alleles to another population. Fertile individuals (emigration & immigration) Seeds Pollen Gametes Genetic Drift Changes in the gene pool of a (small) population due to chance. Chance = random catastrophes random individuals begin a pop. genes randomly passed on to offspring Genetic Drift Genetic Drift Genetic Drift Genetic Drift Genetic Drift Population Bottleneck = genetic drift in small remnant population that later becomes larger. Result: a large genetically similar population Founder effect = genetic drift in small founding population that later becomes larger. Example: polydactyly in the Amish Population Bottleneck p. 403 Population Bottleneck No Genetic Variation Genetic Variation Small Population Much Genetic Drift # Large Population time Large Population Cheetahs Founder Effect No Genetic Variation # time Genetic Variation # time Zoo Animals Nonrandom Mating Assortative Mating = preferentially mating with either similar or different genotypes. Inbreeding = reproducing with relatives; increases homozygosity. (More likely to get 2 copies of the same bad gene. INCEST TABOO) Outbreeding = reproducing with nonrelatives; increases heterozygosity. Natural Selection Phenotype can be determined by a single gene or by many genes. Stabilizing selection = removes extremes. Directional selection = Removes ONE extreme. Disruptive selection = Removes intermediates; favors extremes. Quantitative Characters One Gene Characteristic # Many Gene Characteristic # Directional Selection # p. 405 Distribution # p. 405 Directional selection • เกิดขึ้นเมือแอลลีลหนึ่งมี fitness เหนือแอลลีลอื่นๆ กระบวนการนี้ จะเกิดไปจนกว่าแอลลีลจะฟิ กส์ และประชากรทั้งหมดแสดงฟี โน ไทป์ ที่มีความเหมาะสมนั้น • ตัวอย่าง เช่น ความต้านทานต่อ ปฏิชีวนะ Stabilizing Selection # p. 405 Distribution # p. 405 Disruptive Selection # p. 405 Microevolution Mutation - source of new variation Gene Flow - redistributes variation Genetic Drift - reduces variation (by chance) Non-random mating - maintains (outbreeding) or reduces (inbreeding) variation Natural Selection - reduces variation (due to environment) Hardy-Weinberg Assumptions NO EVOLUTION no mutation population is genetically isolated very large population size random mating no natural selection Hardy-Weinberg Are the assumptions of HardyWeinberg likely to be met? Nope. Why is the equation useful? Modification by terms for pop. size, selection, non-random mating, etc. more realistically model real populations. Hardy-Weinberg Assumptions EVOLUTION mutation gene flow genetic drift assortative mating natural selection Decreasing Variation Genetic Drift - reduces variation (by chance) Inbreeding - reduces variation by increasing homozygosity Natural Selection - reduces variation (due to environment); disadvantaged alleles disappear Maintaining Variation Mutation - creates new alleles Neutral Alleles - do not affect the fitness of an organism; are not removed by natural selection Subpopulations - selection different in different areas but gene flow keeps them “mixing” Dislocation of European bison's subpopulations in Ukraine Maintaining Variation Gene Flow through Sexual Reproduction - new combinations of alleles Polymorphism - two genotypes favored by selection (often frequency dependent) e.g., right mouthed & left mouthed scale eating fishes Heterozygote Advantage heterozygote parents produce some homozygote offspring Right mouthed & Left mouthed scale eating fishes conspicuously asymmetrical left-bending (left) and right-bending (right) individuals of the scale-eating cichlid fish Perissodus microlepis from Lake Tanganyika. (Photo courtesy of A Meyer.) Palmer Journal of Biology 2010 9:11 doi:10.1186/jbiol218 Sickle Cell Disease HbnHbn = “normal” red blood cells; no sickle cell disease HbnHbs = some sickled red blood cells some normal; mild sickle cell disease and some protection from malaria HbsHbs = sickled red blood cells; sickle cell disease causing death and some protection from malaria Sickle Cell Disease In malarial areas: sickle cell malaria HbnHbn none highly susceptible HbnHbs mild low susceptibility HbsHbs death low susceptibility Relationship of Phenotype and Genotype The Genotype codes for the Phenotype -Almost all enzymes are proteins. -Almost all traits are produced by the action of proteins. Genotype Phenotype Genotype and phenotype are not exactly correlated. Environment is important. e.g., human height Phenotypic plasticity - the production of different phenotypes in response to different environments. e.g., white oak leaves • A change in the environment also can affect the phenotype. • Pinkness in flamingos is not encoded into their genotype. • The food they eat makes their phenotype white or pink. Evolutionary Constraint All conceivable mutations are not possible. The organism must still function. All jawed vertebrates have a body plan with 2 pairs of paired appendages. No six legged vertebrates. Evolution must work with what it has. Major reorganization very rare. Evolutionary Constraint p. 411 • Why couldn't terrestrial arthropods evolve to be as large as elephants? • What is an evolutionary constraint? The laws of Physics and Inheritance • Arthropods inherited both an exoskeleton and jointed legs. • These traits have opened up many opportunities in arthropod evolution, but they have also blocked other possibilities. • In particular, there are three constraints on the size of terrestrial arthropods: – Molting: Molting is more hazardous for larger animals. – Exoskeleton strength: The exoskeleton may not be strong enough to support larger animals. – Respiration: Many arthropods can only get enough oxygen to support small bodies. The land-dwelling coconut crab weighs in at 5 kg (over 10lbs). For these giants, molting is a serious commitment: they may spend a whole month in a deep burrow wriggling out of the old skin and waiting for the new one to firm up! Is the physics of molting a constraint on arthropod size? You've just seen that molting out of the exoskeleton may limit the size of terrestrial arthropods. Does the exoskeleton cause other problems for outsized arthropods? To figure out the answer, we'll see what happens to the exoskeleton and the muscles that move it when an arthropod is scaled up. Exoskeleton strength: Blowing up ants What would happen to an ant if it were scaled up, keeping all its body parts in proportion? Each ant below is twice the size of the previous one. See what happens when it gets up to go forage for food. Exoskeleton strength: A solution? So is there any solution to this problem? Well, wider tubes are stronger than narrower ones. Perhaps if we gave our giant ant extra-wide legs with an extra-thick exoskeleton, it wouldn't suffer so many broken limbs. Does this ant look like it might be a winner? Extra large means extra heavy Test.png Test.png The Crustacean/Spider Model The The Insect Insect Model Model Water/air passes over gills/book gills/book lungs and lungs oxygen and diffuses oxygen into the diffusesThe blood. intoblood the blood. carriesThe oxygen throughout the body. blood carries oxygen throughout the body. Tracheae and tracheoles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells. The Crustacean/Spider Model Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body. The Insect Model Tracheae and trachioles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells. Respiration: Gotta have oxygen All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect. All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect. The tubes below represent the tracheae of three dragonflies. In this model, each tube supplies a gut cell with oxygen — the larger the dragonfly, the longer the tube. The blue dots represent oxygen molecules. See how oxygen moves through the tubes. The gut cell in the biggest dragonfly is not doing too well because it is not getting enough oxygen. There is a limit to the length of tracheae (and thus to the size of the dragonfly) that can provide every cell with sufficient oxygen. Conclusion • Evolution is an undirected process, constrained – by physical laws (such as gravity) – by genetics (which might, for example, encode the directions for building breathing organs in a particular way), and – by the environment (which might not, for example, contain a niche for a large, slow-moving, and fragile ant). • In the case of the arthropods, the exoskeleton — a useful adaptation for body support, protection and water retention as well as their respiratory system, may have brought evolutionary constraints along with benefits.