Chapter 8 Natural selection: empirical studies in the wild
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Transcript of Chapter 8 Natural selection: empirical studies in the wild
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Chapter 8Natural selection: empirical
studies in the wild
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Diversity in Darwin’s finches
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Medium ground finch
• Variation in beak size influences efficiency at eating different types of seeds
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Beak size evolution
• Drought resulted in more hard, woody seeds– Favored larger beaked
birds
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Natural selection is variable over time
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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 selection
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Coat color variation affects fitness
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Light coat color evolved independently in different populations
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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 trait
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Natural selection can be variable across space
• Gene flow can bring alleles to new locations– Alleles may increase or decrease fitness
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Aposematism favored only in areas where coral snakes co-occur
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Key Concepts
• Natural selection can lead variation over the geographic range of a species
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Gall flies induce plants to produce galls
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Gall diameter is variable and heritable
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Stabilizing selection on gall size
Intermediate size favored
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Key Concepts
• Stabilizing selection results when agents of selection act in opposing directions
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Eda gene involved in production of lateral plates in stickleback
Marine ancestral form
Freshwater derived form
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Shift in dorsal spine length recorded in fossil record
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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 freshwater
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Ability to digest lactose as adults found in certain populations
- Lactase expression persists into adulthood
- Correlates with domestication of cattle
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Strong evidence for positive selection on lactase persistence alleles
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Artificial selection in crop production
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Artificial selection in crop production
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Gradual increase in cob size documented by archaeologists
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Domestic dog diversity created in last 15,000 years
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Pesticides and herbicides act as agents of selection
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Resistance to pesticides in houseflies
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Rapid evolution of herbicide resistance
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Alteration in EPSPS enzyme leads to Roundup resistance
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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 law
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Introduced cane toads have led to evolution of black snake populations
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Evolution of shorter male horns due to hunting
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Cod fishing has influenced life-history evolution
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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 practices