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UMass Amherst BIOLOGY 280 - Chapter 8-1 (1)

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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Click to edit Master subtitle style 1/12/13 Chapter 8Natural selection: empirical studies in the wild1/12/13 Diversity in Darwin’s finches1/12/13 Medium ground finch•Variation in beak size influences efficiency at eating different types of seeds1/12/13 Beak size evolution•Drought resulted in more hard, woody seeds–Favored larger beaked birds1/12/13 Natural selection is variable over time1/12/13 Key Concepts•Beak size influences fitness and is heritable–Natural selection can cause change•Directional selection favors increases or decreases in the mean of a trait•Stabilizing selection favors average values of a trait•Long-term studies reveal fluctuation in the direction and strength of natural selection1/12/13 Coat color variation affects fitness1/12/13 Light coat color evolved independently in different populations1/12/13 Key Concepts•Evolution in response to natural selection is inevitable if:–There is variation in a trait–Variation is heritable–Some variants reproduce more than others•Specific features of the environment can generate natural selection on a trait1/12/13 Natural selection can be variable across space•Gene flow can bring alleles to new locations–Alleles may increase or decrease fitness1/12/13 Aposematism favored only in areas where coral snakes co-occur1/12/13 Key Concepts•Natural selection can lead variation over the geographic range of a species1/12/13 Gall flies induce plants to produce galls1/12/13 Gall diameter is variable and heritable1/12/13 Stabilizing selection on gall sizeIntermediate size favored1/12/13 Key Concepts•Stabilizing selection results when agents of selection act in opposing directions1/12/13 Eda involved in production of lateral plates in sticklebackMarine ancestral formFreshwater derived form1/12/13 Lateral plate reduction recorded in fossil record1/12/13 Low Eda allele favored in freshwater populations•Production of armor energetically costly –Little predation pressure to counterbalance•Low Eda allele present at low frequency in marine environment–Favored when introduced to freshwater1/12/13 Key Concepts•Populations that independently experience parallel environmental changes represent replicated natural experiments1/12/13 Ability to digest lactose as adults found in certain populations-Lactase expression persists into adulthood-Correlates with domestication of cattle1/12/13 Pattern of genetic linkage indicates history of selective sweep1/12/13 Strong evidence for positive selection on lactase persistence alleles1/12/13 Artificial selection in crop production1/12/13 Artificial selection in crop production1/12/13 Gradual increase in cob size documented by archaeologists1/12/13 Domestic dog diversity created in last 15,000 years1/12/13 Pesticides and herbicides act as agents of selection1/12/13 Resistance to pesticides in houseflies1/12/13 Rapid evolution of herbicide resistance1/12/13 Alteration in EPSPS enzyme leads to Roundup resistance1/12/13 Creation of refuges can slow the evolution of resistance•Bt crops select for resistance in pests–Comes at a cost when Bt is not present•Creation of Bt-free refuges favors Bt-susceptible insects–Slows evolution of resistance•Refuges are now required by law1/12/13 Introduced cane toads have led to evolution of black snake populations1/12/13 Evolution of shorter male horns due to hunting1/12/13 Cod fishing has influenced life-history evolution1/12/131/12/13 Key Concepts•The speed of evolution depends on amount of genetic variation and strength of selection–Leads to rapid resistance in pest populations•An understanding of evolutionary biology can lead to novel management


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