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BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Darwin • 1835 _____________visited the Galapagos Islands and became convinced various populations evolved from ancestral form. • 1838 After reading an essay by __________________, he theorized some individuals would have a competitive advantage conferred by favorable characteristics. 1 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Darwin’s Theory of Natural Selection • • – Some are heritable. • • 2 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection • Augustinian Monk – Studied garden pea (Pisum sativum). – Discovered characteristics pass from parent to offspring in form of discrete packets called genes. • Exist in alternate forms - alleles. • Some prevent expression of others. 3 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Big Picture… • Phenotypic variation among individuals in a population results from the combined effects of … 4 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Big Picture… • The Hardy-Weinberg equilibrium model helps identify … 5 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Big Picture… • ________________ is differential survival and reproduction among phenotypes. 6 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Big Picture… • The extent to which phenotypic variation is due to genetic variation determines …. 7 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Big Picture… • Random processes, such as genetic drift, can… 8 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Variation Within Populations • Variation in Plant Populations – Many plant species differ dramatically in form from one elevation to another. • Clausen et al. found evidence of adaptation by ecotypes to local environmental conditions in Potentilla glandulosa. – 9 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Variation Within Populations • Variation in Plant Populations – Phenotypic differences (growth and flower production) within clones grown at the 3 elevations are the result of environmental differences • 10 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection 11 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Variation in Animal Populations • Genetic Variation in Alpine Fish – Movement of cold adapted aquatic species into the headwaters of glacial valleys that lace the Alps created clusters of geographically isolated populations. • Douglas and Brunner used microsatellite DNA to conclude Coregonus populations are … 12 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Hardy Weinberg • Hardy Weinberg principle states that in a population mating at random in the absence of evolutionary forces, allele frequencies will remain constant. 13 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Calculating Gene Frequencies • SS (81%) SA (18%) AA (1%) – Frequency of S allele ? • = – 14 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Conditions Necessary for Hardy Weinberg • • • • • …Between All Genotypes – Likely, at least one of these will not be met and allele frequencies will change. • Potential for evolutionary change in natural populations is very great. 15 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Natural Selection • Some individuals in a population, because of their phenotypic characteristics, will have higher survival and produce more offspring. – ________________ is the measure of an individual’s contribution of offspring, or genes, to future generations. – Natural selection can… 16 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Stabilizing Selection • __________________ acts to impede changes in a population by acting against extreme phenotypes and favoring average phenotypes. 17 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Directional Selection • ____________________ leads to changes in phenotypes by favoring an extreme phenotype over other phenotypes in the population. 18 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Disruptive Selection • ________________ creates bimodal distributions by favoring two or more extreme phenotypes over the average phenotype in a population. 19 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Evolution by Natural Selection • Natural selection, which changes genotypic and phenotypic frequencies in populations, can result in adaptation to the environment. – Depends on ________________ of trait. h2 = VG / VP • VG : Genetic variance • VP: Phenotypic variance 20 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Adaptive Change in Colonizing Lizards • Losos et al. – Genus Anolis • Great diversity includes large amount of variation in size and body proportions. – Length of hind limbs appears to reflect … » Diameter of perching surfaces. 21 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Rapid Adaptation by Soapberry Bugs • Carroll and Boyd – Soapberry Bug (Jadera haematoloma) feeds on seeds from family Sapindaceae. • Slender beaks to pierce fruit walls. – Distance from outside fruit wall to seeds varies widely - … » Found close relationship between … 22 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Change Due To Chance • Working in teams complete the simulation on Population Genetics… 23 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Change Due To Chance • Random processes such as _____________ can change gene frequencies in populations, especially in small populations. • Major concern of ____________________ is reducing habitat availability to the point where genetic drift will reduce genetic diversity within natural populations. 24 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Evidence of Genetic Drift in Chihuahua Spruce • Picea chihuahuana now restricted to peaks of Sierra Madre Occidental in N. Mexico. – Ledig et al. examined populations to determine if the species has lost genetic diversity as a consequence of reduced population size. • Found significant … 25 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Genetic Variation In Island Populations • In general, genetic variation is _________ in isolated and generally smaller, island populations. – Reduced genetic variation indicates a lower potential for a population to evolve. 26 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Genetic Diversity and Butterfly Extinctions • Frankham and Ralls point out ___________ may be a contributor to higher extinction rates in small populations. – Reduced fecundity, depressed juvenile survival, shortened life-span. • Saccheri et al. conducted genetic studies on populations of Glanville fritillary butterflies (Melitacea cinxia). – Populations with highest levels of inbreeding had… 27 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Evolution and Agriculture • “_____________________” is used to describe selective breeding of domesticated organisms to produce or maintain desirable traits. • “_____________________” is the introduction or deletion of genes in domesticated organisms. – These organisms are termed “genetically modified organisms” or GMOs. 28 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection Unintended Evolutionary Consequences • The use of chemicals in agriculture can have evolutionary consequences – Plant and animal pests may evolve resistance to the chemicals used to control them • Resistance among pests have been shown to be quick and widespread – Vila-Aiub et al. showed how Johnsongrass quickly evolved resistance to herbicides in Argentina 29 BIOL 3240 Plant and Animal Ecology – Population Genetics and Natural Selection 30