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Natural Selection without evolution:-Identical plants were planted in identical plots, one plot was fertilized and one left unfertilized. Here we have cause for NS: 1. phenotypic variation in flowers and 2. Differential fitness among phenotypes: Fertilized plants produced many flowers and seeds and unfertilized plants produced few flowers and seeds. BUT there is no genetic basis for these phenotypic differences because they are identical plants.-NS occurs in the plants but there is no genetic change, therefore NO EVOLUTION takes place-Types of Natural Selection:oDirectional Selection: selection against certain phenotypes which push the population phenotype in one directionEx: horsesbecoming larger, cheetahsbecoming smallerPeppered moth: pollution is believed to have caused the changein colorationGuppies: great evolutionary study organisms; the evolution of spots was trying to be understood, they found out that spot number is genetically related (really stabilizing)Put population of guppies in a fish tank and watched thespot number change over time- in the tanks with just guppies spot number went up over time; found out that males with more spots are more likely to get a mateInsecticides: insects have evolved to become more and more resistant towards insecticidesoStabilizing Selection: selection acts against the extremes, thus left with intermediate valuesBirth weights: weight extremes have a higher rate of dyingGuppies:when predators in the fish tank, over time the numberof spots decreased in the population because they were more visible. Due to females liking spots and predators seeing spots the selection is stabilized.oDiversifying Selection: selection for two extremes and selection against intermediatesOpposite of stabilizingMean won’t change much in population but the variability will
Finches: bill size in seed-cracking finchesAfrican swallowtails: Wing colorLecture 2Constraints on EvolutionEvolution by NS almost always improves fitness (adaptation)NS does not produce an optimal organism, but a better fit organismEvolutionary constraints: factors which prevent evolution of optimal designoChanging environment for peppered mothoLaws of physics for horse heightoGenetic limitations for spot number in guppiesGenetic Drift-Genetic Driftis a random change in allele frequency in a population from one generation to the nextoOccurs primarily in small populations: endangered species or founding populationsoGenetic drift can prevent adaptive evolutionoWhen is drift more important than NS in the evolution of a population?When populations size (N) is smallWhen the strength of NS (s) is weakIf selection is under 5% then genetic drift is more important when there is small populationThe weaker the selection the smaller the populationcan beIf s if less than 1/N, then genetic drift is more important than NSFruit fly experiment: Random sample of 8 female and 8 males from all 107 populations respectively were selected when starting out with