Evolution

1. Evolution

2. Genetic variation There can be no evolution without variation Mutations are the ultimate source of new variation in DNA Germ-line mutations are important for evolution

3. Genetic variation in natural populations Natural populations exhibit great variation. Heterozygosity is approximately 10% for all loci.

4. Maintaining genetic variation Adaptive genetic diversity Balanced between origin of variation by mutation and the loss by selection Neutral genetic diversity Balance between origin of variation by mutation and loss by drift

6. Overdominance Selection favoring overdominance • favors heterozygotes • results in stable gene frequencies fitness SS SA AA

7. Overdominance: Sickle Cell Anemia

8. Overdominance: Sickle Cell Anemia SS = sickle-cell anemia SA = malaria resistance AA = Malaria susceptability

9. Sickle-cell anemia

10. Balancing Selection Case in which natural selection maintains genetic variation at frequencies above levels of mutation. …in this case, balancing selection makes the population as a whole more resistant to malaria

11. Prion disease in Fore Tribespeople Kuru (prion disease related to Mad Cow disease) resulted from cannibalism Only heterozygotes for the Prion Protein Gene (PRNP) are resistant

12. Underdominance Underdominance • heterozygotes have a lower fitness • results in an unstable equilibrium • Uncommon and few natural examples fitness SS SA AA

13. Other forms of selection….

14. Frequency-dependent selection

17. male andromorph gynomorph

18. andromorph

19. Rare male effect Rare male effect (negative frequency dependent mating success)

20. Stabilizing Selection Selection that eliminates the extremes of a distribution and favors the centre

21. Stabilizing Selection Stabilizing selection is common in quantitative traits.

22. Disruptive Selection Selection that favors the extremes and eliminates the middle of a frequency distribution of trait values

23. Dull yearlings allowed to nest on territory Bright yearlings can hold their own

24. Disruptive Selection Selection that favors the extremes and eliminates the middle of a frequency distribution of trait values

30. Expression of variation

31. Expression of variation

32. Feather modification

33. Feather modification

34. Environmentally-induced phenotypic responses Induced response: One genotype produces multiple phenotypes

35. Environmentally induced response Daphnia can produce helmets and spines if predators are present

37. Other responses Barnacles will change shape of growth if a predator snail present Snails change offspring number, shell size, shell organic content in utero in presence of crayfish

38. And Matt’s favorite….

42. Phenotypes and reaction norms GENOTYPE PHENOTYPE

43. Phenotypes and reaction norms GENOTYPE PHENOTYPE X ENVIRONMENT

44. Phenotypes and reaction norms GENOTYPE PHENOTYPE X ENVIRONMENT

45. No genetic variation underlying number of digits, so no sensitivity to population density Fecundity is much more sensitive to fecundity, and some genotypes more than others

46. So, is phenotypic plasticity adaptive?

47. The reaction norms themselves can be subject to selection Selection to increase sensitivity to population density would lead to the increase in frequency of G1 Selection to decrease sensitivity to density would increase the frequency of G3