Chapter 8 Natural selection: empirical studies in the wild

1. Chapter 8Natural selection: empirical studies in the wild

2. Diversity in Darwin’s finches

3. Medium ground finch • Variation in beak size influences efficiency at eating different types of seeds

4. Beak size evolution • Drought resulted in more hard, woody seeds • Favored larger beaked birds

5. Natural selection is variable over time

6. 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

7. Coat color variation affects fitness

8. Light coat color evolved independently in different populations

9. 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

10. Natural selection can be variable across space • Gene flow can bring alleles to new locations • Alleles may increase or decrease fitness

11. Aposematism favored only in areas where coral snakes co-occur

12. Key Concepts • Natural selection can lead variation over the geographic range of a species

13. Gall flies induce plants to produce galls

14. Gall diameter is variable and heritable

15. Stabilizing selection on gall size Intermediate size favored

16. Key Concepts • Stabilizing selection results when agents of selection act in opposing directions

17. Edageneinvolved in production of lateral plates in stickleback Marine ancestral form Freshwater derived form

18. Shift in dorsal spine length recorded in fossil record

19. Low Edaallele favored in freshwater populations • Production of armor energetically costly • Little predation pressure to counterbalance • Low Edaallele present at low frequency in marine environment • Favored when introduced to freshwater

20. Ability to digest lactose as adults found in certain populations • Lactase expression persists into adulthood • Correlates with domestication of cattle

21. Strong evidence for positive selection on lactase persistence alleles

22. Artificial selection in crop production

23. Artificial selection in crop production

24. Gradual increase in cob size documented by archaeologists

25. Domestic dog diversity created in last 15,000 years

26. Pesticides and herbicides act as agents of selection

27. Resistance to pesticides in houseflies

28. Rapid evolution of herbicide resistance

29. Alteration in EPSPS enzyme leads to Roundup resistance

30. 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

31. Introduced cane toads have led to evolution of black snake populations

32. Evolution of shorter male horns due to hunting

33. Cod fishing has influenced life-history evolution

35. 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