Transcript Lecture 13
Evolution Pleistocene glyptodont Do not post on Figure 17.5a Page 276 Adaptation What do these bugs have in common? A flower mantid in Malaysia A leaf mantid in Costa Rica Darwin’s Voyage • Studied theology • At age 22, 5yr, voyage on the Beagle • Similarities between living and fossil organisms Figure 13.1A Figure 13.4 Galapagos Islands Darwin Wolf Pinta Genovesa Marchena Santiago Bartolomé Fernandia Seymour Baltra Rabida Pinzon Santa Cruz Santa Fe Tortuga San Cristobal Isabela Española Floreana Figure 13.5 Early Ideas •Aristotle •Judeo-Christian culture •Lamarck – Inheritance of acquired traits Geology • Geologists proposed… – Very old Earth – Changed by gradual processes Descent with Modification •Darwin and Wallace •1859 On the Origin of Species •Natural Selection – The mechanism of evolution – Artificial selection? Artificial Selection Hundreds to thousands of years of breeding (artificial selection) Ancestral dog (wolf) Figure 13.2A Figure 13.2B Natural Selection Living species… …Are descended from earlier forms African wild dog Coyote Wolf Thousands to millions of years of natural selection Figure 13.2C Ancestral canine Fox Jackal Evidence for Evolution •Fossils A Skull of Homo erectus B Petrified tree E Fossilized organic matter of a leaf C Ammonite casts D Dinosaur tracks F Insect in amber G “Ice Man” Figure 13.7 Evidence for Evolution •The fossil record – Time lines Figure 13.3H Evidence for Evolution •Fossils link extinct species w/ living species Figure 13.3I Evidence for Evolution •Biogeography – Geographic distribution of species – Why are marsupials found mostly in Australia? Figure 13.10 Evidence for Evolution •Comparative anatomy – Homologous structures • Figure 13.4A similar characteristics from common ancestry Human Cat Whale Bat Evidence for Evolution •Comparative Embryology Pharyngeal pouches Post-anal tail Human embryo Chick embryo Figure 13.4B Evidence for Evolution •Molecular Biology – Comparing DNA between different organisms Table 13.4 Natural Selection • Darwin’s observations – Overproduction – Individual variation – Differential reproductive success • Who will survive and reproduce? Natural Selection •Natural selection – Certain traits increase survival – Those indiv. influence the future •Where can we observe changes in traits? Figure 13.14 Population Evolve What is a population? Population genetics Populations Evolve • Gene pool – All genes in a population • Sources of genetic variation – Mutations – Meiosis – Fertilization Populations Evolve • Individuals don’t evolve! • Evolution is change in frequency of traits in a population! Populations Evolve • Or not? •What would a nonevolving population look like? •Stable allele frequency Hardy-Weinberg Equilibrium – Genes are shuffled during sexual reproduction – does not alter the proportions of alleles – P2 + 2pq + q2 = 1 Phenotypes Genotypes Number of animals (total 500) Genotype frequencies Number of alleles in gene pool (total 1,000) Allele frequencies Figure 13.7B WW 320 320 0.64 500 640 W 800 0.8 W 1,000 Ww ww 160 20 160 0.32 500 160 W 160 w 20 0.04 500 40 w 200 0.2 w 1,000 Genetic Equilibrium • No mutation • Large population • Isolation • Everyone reproduces • Random mating Microevolution • Drives a population away from equilibrium: Natural selection and… – Gene flow – Genetic drift – Mutations Genetic Drift • Random fluctuation of allele frequencies overtime • More pronounced in small populations Figure 13.22 Computer Simulation 1.0 AA in five populations 0.5 allele A lost from four populations 0 1 5 10 15 20 25 30 35 40 45 50 Generation (25 stoneflies at the start of each) Computer Simulation 1.0 0.5 allele A neither lost nor fixed 0 1 5 10 15 20 25 30 35 40 45 Generation (500 stoneflies at the start of each) 50 Bottleneck Effect • A severe reduction in population size • Lots of drift • Example – Elephant seals 20 individuals – rebounded to 30,000 Bottleneck Original population Bottlenecking event Figure 13.9A Surviving population Figure 13.9B Figure 13.24 Inbreeding • • • • Leads to increased homozygosity Can lower fitness More recessive alleles are expressed Amish, cheetahs Founder Effect • A few individuals start a new population • Allele frequencies of founders may be different from original population Figure 13.25 Gene Flow • Genes move in/out of a population • Immigration/emigration • Minimizes genetic variation between populations Mutations • Infrequent – Lethal – Neutral – Advantageous Natural Selection Revisited • Largest impact • Successful alleles = successful phenotypes • Who will reproduce? • What will happen to allele frequencies? • Increased fitness! in the population Number of individuals Number of individuals in the population • Directional Selection Range of values for the trait at time 1 Range of values for the trait at time 2 Number of individuals in the population Natural Selection Revisited Range of values for the trait at time 3 Antibiotic Resistance • Since 1940s • Overuse • Resistant forms Number of individuals in the population Natural Selection Revisited Range of values for the trait at time 1 • Stabilizing Selection Range of values for the trait at time 2 Range of values for the trait at time 3 Number of individuals Number of individuals in the population in the population • Disruptive Selection Range of values for the trait at time 1 Range of values for the trait at time 2 Number of individuals in the population Natural Selection Revisited Range of values for the trait at time 3 Sexual Selection Question of the Day Antibiotic resistant bacteria are showing up all over the place. The infamous “flesh eating” bacteria is an example. What are two things that you can do to help prevent more bacteria from becoming antibiotic resistant?