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Bio 178 Lecture 32 Evolution and the Origin of Species J. Elson-Riggins Reading • Chapters 21, 22, 23, 25, & 1 Quiz Material • Questions on P 452, 470, 490, 530, & 18 • Chapters 21, 22, 23, 25, & 1 Quizzes on Text Website (www.mhhe.com/raven7) Changing Allele Frequencies (Cntd.) • Genetic Drift Random change in allele frequencies of a population as a result of chance events. Founder Effects One or a few individuals leave a population and establish a new one. The alleles of these founders will be very significant in the new population, even if they were rare in the original population. Eg. Galápagos Islands. Founder Effect Founder Effect © S. Riggins Genetic Drift (Cntd.) Bottleneck Effect Occurs when the population is drastically reduced to a few individuals by a chance event - a random genetic sample of the initial population will remain and genetic variability will be restricted. Eg. Northern elephant seal: ~ 20 animals ~1900, now ~130,000 animals. Bottleneck Effect Disseminated Intravascular Coagulation Lungs from Infected NES Changing Allele Frequencies (Cntd.) • Selection Process by which some organisms leave more offspring than others. Artificial Selection Breeder selects the desired characteristics. Natural Selection Environment determines which individuals survive. (Natural selection is one of several processes that can cause evolutionary change). Frequency Dependent Selection Heterozygote Advantage Fitness Reproductive success of an individual. Dependent on: • Survival time • Mating frequency • Number of offspring per mating Forms of Selection Selective changes to the population depend on which genotypes are favored. • Disruptive Selection Intermediate phenotypes are selected against, eg. African fire-bellied seedcracker finch. Disruptive Selection Forms of Selection (Cntd.) • Directional Selection Individuals of one extreme phenotype are selected against. Forms of Selection (Cntd.) • Stabilizing Selection Individuals of both extremes are selected against, eg. Weight of human newborns. Stabilizing selection Evidence for Evolution by Natural Selection • Darwin’s Finches Collection In 1835, Darwin collected 31 individual finches from 3 Galápagos Islands - represented 13 species, all similar except for their bills. Importance of the Bill The size and shape of bill correlated with their food source each bill type is adapted for its function evidence for natural selection. Recent Evidence - P. and R. Grant Read P 455. Resource Partitioning In Darwin’s Finches Finch from San Cristobal Island ©J. Elson-Riggins Evidence for Evolution by Natural Selection • Industrial Melanism and Peppered Moths Biston betularia Adults range from “peppered” to melanic - due to different alleles in the population. Black is dominant. Pre-1850 Birmingham, England Black moths rare. Post-1850 Increasing proportion of black moths, up to 100% of certain populations. Biston betularia Industrial Melanism (Cntd.) Why did the Allele Frequency Change? Read about Tutt’s hypothesis (1896) and Kettlewell’s experiment (1950’s). Industrial Melanism Process by which darker individuals become more frequent than lighter individuals in industrialized areas due to natural selection. Selection Against Melanism Has occurred since the Clean Air Act of 1956. Current Controversy - What is the agent of Natural Selection? Read P 457. Selection Against Melanism Evidence for Evolution by Natural Selection • Artificial Selection By selecting for desirable phenotypic traits, humans have produced evolutionary change over short periods of time. Agriculture and Lab Experiments Read P 458 Domestication Example - domestic dogs. Selection for desirable traits has resulted in huge phenotypic variation in only 10,000 years. Domestic Dog Breeds Fossil Evidence for Evolution • The Fossil Record Fossilization Occurs rarely, but enough fossils have been found to provide information on evolution. Successive Evolutionary change Fossil record documents life from the origin of eukaryotes on. Gaps in the Fossil Record Due to problems with the fossilization process and recovery. Some major gaps filled recently, eg. Missing links in cetacean evolution - recent discoveries of Ambulocetus, Rodhocetus, & Pakicetus. History of Life Revealed by Fossil Record Missing Links in Evolution of Cetaceans Evolution of Oyster Shell Shape Fossil Evidence for Evolution • Horse Evolution Over 60 million years, the horse has evolved from a small 4-toed, short-legged mammal adapted to woodland, to its current form, which is adapted for open grassland. Hyracotherium sandrae Although, due to lack of horse diversity its evolution appears linear, there were actually 13 genera of horses in N. America in the Miocene epoch. Horse Evolution - Body Size Horse Evolution Evidence for Evolution (Cntd.) • The Anatomical Record 1. Sharing the Same Parts * Homologous Structures Structures that (although they differ in form and function) are derived from the same body part of a common ancestor. Eg. Bones of vertebrate limbs. * Analogous Structures Features that resemble one another as a consequence of the same selective pressures, but were formed from different structures (not from a common ancestral origin). Eg. Wings of insects and birds. Homology - Vertebrate Bones The Anatomical Record (Cntd.) 2. Development Embryonic development of vertebrate embryos is similar suggests a common ancestor. Eg. All at one stage have gills and a tail. 3. Imperfect Structures Not all organisms are perfectly adapted to their environments - a consequence of selection acting on the variation available in the population (random rather than by design). Eg. Blind spot of vertebrate eye compared to mollusk eye, giraffe neck vertebrae. Vertebrate Development Vertebrate and Mollusk Eyes The Anatomical Record (Cntd.) 3. Vestigial Structures Structures that had a function in the original ancestor, but have no obvious function in the descendent (diminished structure with reduced significance) - strong evidence for evolution. Examples: Human appendix - Is the terminal part of the cecum. Is small and vermiform, a vestige of the cecum of our herbivorous ancestors. Whale pelvic bones - reduced. Cecum and Appendix of Mammals http://www.talkorigins.org/faqs/vestiges/appendix.html Whale Pelvic Bones Evidence for Evolution (Cntd.) • The Molecular Record 1. Sequence Divergence Evolutionary changes occur by nucleotide change. Hypothesis - More distantly related organisms expected to have more differences in their DNA sequences than closely related organisms. Tested by comparing the sequence divergence of organisms to the anatomical/fossil records - does the molecular record match the anatomical/fossil records? Use non-coding sequences - closely related organisms will only have a similar sequence if evolution has occurred. The Molecular Record (Cntd.) 2. Phylogenetic Trees • Represent the evolutionary history of a group of organisms. Can be based on a variety of characteristics. Molecular data frequently used, eg. rRNA spacer regions. • Anatomical/fossil and molecular data largely in agreement. Fig. 25.11 Molecular Clock of Cytochrome c Suggests progressive change over time: Evidence for Evolution (Cntd.) • Convergent Evolution The independent development of similar structures in organisms that are not directly related. Occurs as a consequence of the same selective pressures similar environments. Example: Marsupial-Placental Convergence Despite isolation, Australian marsupials resemble placental mammals occupying the same niches (functional role in its environment) on other continents. Convergent Evolution Evidence for Evolution (Cntd.) • Island Evolution Organisms on islands tend to most closely resemble the organisms living on the nearest continent - suggests that they have common ancestors. Eg. Darwin’s finches and Galápagos tortoises most closely resemble S. American finches & tortoises. Voyage of H.M.S. Beagle Darwin (1809-1882) and his Evidence Read P 8-14 • Fossils Living organisms often resemble fossils found in the same area - did one give rise to the other? • Geographical Distribution Characteristics of similar species vary from place to place - do organisms change as they migrate? Criticism of the Theory of Evolution Read P 468. The Biological Species Concept Ernst Mayr (1942) “Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups”. ie. A species is composed of populations that COULD interbreed to produce fertile offspring. But, different species are reproductively isolated. • Problems with the BSC Many problems (eg. asexual organisms) other species concepts exist. Read P 477. The Process of Speciation Similar populations diverge until reproductive isolation results Separate species • Populations adapt to their environment or random changes may occur in separate populations. • Adaptation or random changes result in the accumulation of many differences between the populations. • Isolating mechanisms prevent population hybridization. • The populations are no longer capable of interbreeding successfully. Mechanisms of Reproductive Isolation Liger http://www.sierrasafa rizoo.com/animals/li ger.htm Tigon Behavioral Isolation Classification of Organisms • Binomial System (Carolus Linnaeus (1707-1778) Each organism is given a 2 part name, genus and species. Example: Homo sapiens H. sapiens • Taxonomic Hierarchy 1. Species 5. Class 2. Genus 6. Phylum 3. Family 7. Kingdom 4. Order 8. Domain Taxonomic Hierarchy The Six Kingdom, 3 Domain System Carl Woese (1990) • Kingdoms 2 prokaryote kingdoms: Archaebacteria Eubacteria 4 eukaryote kingdoms: Protista Fungi Plantae Animalia • Domains Bacteria Archaea Eukarya Evolutionary Relationship of the 3 Domains The End! © J. Elson-Riggins