1. III. A Closer Look at Natural Selection A. Natural selection, adaptation, and evolution B. Patterns of natural selection 1. Directional selection 2. Stabilizing selection 3. Diversifying selection C. Effects of selection on the distribution of phenotypes

2. Fig. 23. 12

3. Frequency Phenotype (trait) before Fitness (W) Phenotype (trait) 1 0 Directional selection Pattern Effect

4. Frequency Phenotype (trait) before after Fitness (W) Phenotype (trait) 1 0 Directional selection Pattern Effect

6. Mallett, J. 1989. TREE 4: 336 Pesticide Pesticide application Pesticide % resistant

7. Fig 22.13

8. Evolution of antibiotic resistance Source: Otaya, 1971. Epidemiological study of erythromycin resistance in Staphylococcus aureus in Japan. In Drug Resistance in Bacteria. 1. Macrolide antibiotics. Edited by S. Mitsuhashi. University Park Press, Baltimore.

11. Guppies Poecilia reticulata 5 cm

12. smalllarge Size of predators in pool Size of adult guppies in pool

13. Adult guppy size in each pool Number of guppies Guppy size is variable

14. In lab without any predators…. Time (generations) Guppy size Guppy size is heritable (genetic)

15. Big predator – Pike-Cichlid Crenicichla alta 16 cm Smaller predator – Killifish Rivulus harti 10 cm eats large guppies eats small guppies Guppy size affects survival to reproduce

16. Large predators eat large guppies, more small size alleles passed on Small predators eat small guppies, more large size alleles passed on B – large size B’ - small size

17. Time (generations) Adult guppy size Transplant to Small predator pool Control (stay in Large predator pool Mostly small alleles At beginning

18. Frequency Phenotype (trait) before after Fitness (W) Phenotype (trait) 1 0 Stabilizing selection Pattern Effect

19. Stabilizing selection in humans

20. Too many chicks? Too few eggs? Stabilizing selection on number of eggs in starlings

21. Conflict and Cooperation Parent-offspring conflict Sibling conflict Inclusive fitness and kin selection B r – C > 0 (benefits to recipient * relatedness – costs to giver) Reciprocal Altruism: If costs are small, benefits are large and altruistic acts are reciprocated – altruism can evolve

22. Frequency Phenotype (trait) before after Fitness (W) Phenotype (trait) 1 0 Disruptive selection Pattern Effect

23. Male Lazuli Buntings showing variation in the brightness of their breeding plumage Low plumage Brightness score High plumage Brightness score

24. Plumage brightness From Greene et al 2000, Nature 407:1000-1003

25. Diversifying selection on coat color in deer mice Dark color is favored on rich soil Light color is favored on sandy soil

26. Frequency dependent selection Why are there equal numbers of males and females?

27. Sexual Selection

28. Fig. 23. 12 Effects of selection on phenotype distributions Location of curve = mean Width of curve = variance

29. Frequency Phenotype (trait) beforeafter Possible effect of continual directional selection Eventually variance might decrease Frequency Phenotype (trait) beforeafter Phenotype (trait) before after

30. Frequency Phenotype (trait) before after Possible effect of continual stabilizing selection Variance decreases to none Frequency Phenotype (trait) before after Frequency Phenotype (trait) before after

32. Electrophoresis - separates proteins based on differences in size and electrical charge Heterozygous Homozygous fast Homozygous slow

33. Survey of electrophoretic variation in natural populations **

34. The Paradox of Variation: Evolution requires variation, but natural selection eliminates variation.

35. Dominant traits can hide recessive traits from selection

36. Fig 14.11 Epistasis can hide dominant alleles from natural selection C= pigment c = none B = deposition of lots of pigment (black) b = less deposition (brown) If cc, fur is white regardless of genotype at B locus

37. Good gene Bad gene Genetic hitchhiking: tight linkage to a favorable gene can protect a less favorable gene from selection.

38. SusceptibilityRelative GenotypeRBCto malariafitness HB+ Hb+normalhighestintermediate Hb+ Hbsnormal*lowerhighest Hbs Hbssickledlowerlowest Heterozygote advantage in Sickle cell anemia : Hb+ = normal RBC (co-dominant)Hbs = sickled RBC

40. Diversifying selection in time: Snow goose Nesting habitat

41. Diversifying selection in space: Deer mice Dark color is favored on rich soil Light color is favored on sandy soil

42. Diversifying selection over density: sea urchins