Understanding Selection: Measuring Fitness and Interactive Effects

1. E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection

2. E. Selection 4. Types of Selection - Directional

3. E. Selection 4. Types of Selection - Directional

4. E. Selection 4. Types of Selection - Stabilizing Not necessarily selection for heterozygote!

5. E. Selection 4. Types of Selection - Disruptive Lab experiment – “bidirectional selection” – create two lines by directionally selecting for extremes. Populations are ‘isolated’ and don’t reproduce.

6. E. Selection 4. Types of Selection - Disruptive African Fire-Bellied Seed Crackers

7. E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Frequency-Dependent Selection The selective value depends on the frequency of the allele/phenotype in the population. “rare mate phenomenon” = negative frequency dependence

8. Elderflower orchids: - don’t produce nectar - bumblebees visit most common flower color and get discouraged, try the other color…. Back and forth. - visit equal NUMBERS of the two colors, but that means that a greater proportion of the rarer flower color is visited. As phenotype gets rare, fitness increases. Maintains alleles in population

9. (of yellow flowers)

11. - Morphs of Heliconius melpomene and H. erato Mullerian complex between two distasteful species... positive frequency dependence in both populations to look like the most abundant morph in a given area

12. E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Interactive Effects

13. E. Selection 1. Measuring “fitness” – differential reproductive success 2. Relationships with Energy Budgets 3. Modeling Selection 4. Types of Selection 5. Interactive Effects - antagonistic pleiotropy

14. Pleiotropy Ester1 allele: confers resistance to insecticide, but increases risk of predation. Increased in frequency along coast of France, where spraying occurred (benefit > cost) Did not increase inland much (did increase due to migration), as cost > benefit and selected against

15. Ester1 was eventually replaced by the Ester4 allele, which conferred a weaker benefit for pesticide resistance BUT had no negative effects inland… so the net benefit was greater.

16. E. Selection 5. Interactive Effects - mutation-selection balance A deleterious allele (selectively disadvantageous) can be maintained in a population by mutation: Δq = m – sq2 = rate they are added by mutation – rate lost by selection against the homozygous genotype. qeq = √m/s

17. E. Selection 5. Interactive Effects - mutation-selection balance - selection and drift

18. Deterministic Effects of Selection > Random Effects of Drift At small sizes, it is possible to lose an adaptive allele. However, just by chance, adaptive alleles can become fixed – rapidly increasing the reproductive success of population

19. Darwin • Genetics • Population Genetics and The Modern Synthesis • Modern Evolutionary Theory A. Peripatric Speciation

20. Darwin • Genetics • Population Genetics and The Modern Synthesis • Modern Evolutionary Theory A. Peripatric Speciation B. Punctuated Equilibrium Niles Eldridge Stephen J. Gould

21. B. Punctuated Equilibrium – Eldridge and Gould 1. Consider a large, well-adapted population VARIATION TIME

22. B. Punctuated Equilibrium – Eldridge and Gould 1. Consider a large, well-adapted population Effects of Selection and Drift are small - little change over time VARIATION TIME

23. B. Punctuated Equilibrium – Eldridge and Gould 2. There are always small sub-populations "budding off" along the periphery of a species range... VARIATION TIME

24. B. Punctuated Equilibrium – Eldridge and Gould 2. Most will go extinct, but some may survive... X VARIATION X X TIME

25. B. Punctuated Equilibrium – Eldridge and Gould 2. These surviving populations will initially be small, and in a new environment...so the effects of Selection and Drift should be strong... X VARIATION X X TIME

26. B. Punctuated Equilibrium – Eldridge and Gould 3. These populations will change rapidly in response... X VARIATION X X TIME

27. B. Punctuated Equilibrium – Eldridge and Gould 3. These populations will change rapidly in response... and as they adapt (in response to selection), their populations should increase in size (because of increasing reproductive success, by definition). X VARIATION X X TIME

28. B. Punctuated Equilibrium – Eldridge and Gould 3. As population increases in size, effects of drift decline... and as a population becomes better adapted, the effects of selection decline... so the rate of evolutionary change declines... X VARIATION X X TIME

29. B. Punctuated Equilibrium – Eldridge and Gould 4. And we have large, well-adapted populations that will remain static as long as the environment is stable... X VARIATION X X TIME

30. B. Punctuated Equilibrium – Eldridge and Gould 5. Since small, short-lived populations are less likely to leave a fossil, the fossil record can appear 'discontinuous' or 'imperfect' X VARIATION X X TIME

31. B. Punctuated Equilibrium – Eldridge and Gould 5. Large pop's may leave a fossil.... X VARIATION X X TIME

32. B. Punctuated Equilibrium – Eldridge and Gould 5. Small, short-lived populations probably won't... X VARIATION X X TIME

33. B. Punctuated Equilibrium – Eldridge and Gould 6. So, the discontinuity in the fossil record is an expected result of our modern understanding of how evolution and speciation occur... X VARIATION X X TIME

34. B. Punctuated Equilibrium – Eldridge and Gould 6. both in time (as we see), and in SPACE (as changing populations are probably NOT in same place as ancestral species). X VARIATION X X TIME

35. Darwin • Genetics • Population Genetics and The Modern Synthesis • Modern Evolutionary Theory A. Peripatric Speciation B. Punctuated Equilibrium C. The Molecular Revolution and The Neutral Theory Motoo Kimura 1924-1994

36. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation Phenotypic variation was often interpreted as having selective value; in fact, most studies confirmed that under one environmental condition or another, there was a difference in fitness among variations. Mayr (1963) "it is altogether unlikely that two genes would have identical selective value under all conditions under which they may coexist in a population. Cases of neutral polymorphism do not exist." With this view, polymorphisms must be maintained by different selective pressures in different environments

37. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation With this view, polymorphisms must be maintained by different selective pressures in different environments The one polymorphic species of Papilio darnadus. Variation maintained by selection for different morphs in different parts of its range, that overlap with each of the different toxic models. Three different unpalatable species

38. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation - ‘60’s – lots of electrophoretic work: LOTS of genetic variation ‘silent’ mutations in DNA do not even affect amino acid sequence – invisible to selection. Many neutral substitution mutations in proteins, too. CCC = Proline CCU = Proline CCA = Proline CCG = Proline

39. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation Most populations showed mean heterozygosities across ALL loci of about 10%. - And, about 20-30% of all loci are polymorphic (have at least 2 alleles with frequencies over 1%). Drosophila has 10,000 loci, so 3000 are polymorphic. At these polymorphic loci, H = .33 Conclusion - lots of variation at a genetic level... is this ALL maintained by selection?

40. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load - As we have seen, selection can reduce the size of a population

41. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load - As we have seen, selection can reduce the size of a population - This is called “hard selection”. Reproduction by survivors must COMPENSATE or the population will decline to zero.

42. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load - As we have seen, selection can reduce the size of a population - This is called “hard selection”. Reproduction by survivors must COMPENSATE or the population will decline to zero. - The stronger selection is (the more aa’s lost), the more comensatry reproduction is necessary.

43. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load This toll on population size is called GENETIC LOAD (L) It increases as the mean fitness of the population decreases. Remember? This is the mean fitness of the population.

44. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load This toll on population size is called GENETIC LOAD (L) It increases as the mean fitness of the population decreases. When there are lots of individuals with low relative fitness, the survivors must reproduce EVEN MORE to COMPENSATE.

45. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load This toll on population size is called GENETIC LOAD (L) L = (optimal fitness – mean fitness) / optimal fitness L = (1 – 0.73) / 1 = 0.27 L = (1 – 0.52) / 1 = 0.48

46. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load Why is this a problem? - The easiest way for selection to maintain variation is through heterosis: selection for the heterozygote (Aa). - But in this situation, lots of homozygotes (AA and aa) die.

47. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load Why is this a problem? - Let's consider even a "best case" scenario: - mean fitness = 1 - H((s+t)/2) - If s and t = .1 (very weak), and H = .33 (average for Drosophila), then the mean fitness = 0.967. - Not bad; not much death due to selection at this locus.

48. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load Why is this a problem? - Let's consider even a "best case" scenario: - mean fitness = 1 - H((s+t)/2) - If s and t = .1 (very weak), and H = .33 (average for Drosophila), then the mean fitness = 0.967. - Not bad; not much death due to selection in this situation. - But there are 3000 polymorphic loci across the genome. So, mean fitness across the genome = (0.967)3000!

49. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load Why is this a problem? - Let's consider even a "best case" scenario: - mean fitness = 1 - H((s+t)/2) - If s and t = .1 (very weak), and H = .33 (average for Drosophila), then the mean fitness = 0.967. - Not bad; not much death due to selection in this situation. - But there are 3000 polymorphic loci across the genome. So, mean fitness across the genome = (0.967)3000! - This is ridiculously LOW (0.19 x 10-44)relative to the best case genome that is heterozygous at every one of the 3000 loci.

50. C. The Molecular Revolution and the Neutral Theory 1. The Issue of Variation 2. The Problem with Selection: Genetic Load Why is this a problem? - Let's consider even a "best case" scenario: - mean fitness = 1 - H((s+t)/2) - If s and t = .1 (very weak), and H = .33 (average for Drosophila), then the mean fitness = 0.967. - Not bad; not much death due to selection in this situation. - But there are 3000 polymorphic loci across the genome. So, mean fitness across the genome = (0.967)3000! - This is ridiculously LOW (0.19 x 10-44)relative to the best case genome that is heterozygous at every one of the 3000 loci. HARD SELECTION CANNOT BE RESPONSIBLE FOR THE VARIATION WE SEE ACROSS THE WHOLE GENOME