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Polygenic traits are Many Gene Traits

Polygenic traits are Many Gene Traits. Individuals. Individuals. Gene. Gene. 1. 1. 2. 2. 3. 3. 4. 4. 5. 5. 6. 6. 7. 7. 8. 8. 9. 9. 10. 10. 11. 11. 1. 1. -. -. +. +. -. -. -. -. +. +. +. +. +. +. +. +. -. -. -. -. +. +. 2. 2. -. -. +. +. -.

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Polygenic traits are Many Gene Traits

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  1. Polygenic traits are Many Gene Traits Individuals Individuals Gene Gene 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 1 1 - - + + - - - - + + + + + + + + - - - - + + 2 2 - - + + - - - - + + + + + + + + - - + + - 3 3 - - - - + + - - - - + + - - - - - - - - 4 4 - - + + - - + + + + + + + + + + + + - - + + 5 5 - - - - + + + + - - + + - - - - - - - + + 6 6 - - - - + + - - + + + + - - + + - - + + + + Trait Value 0 0 3 3 3 3 2 2 4 4 6 6 3 3 4 4 2 2 1 1 5 5 Number of individuals Trait value

  2. Individuals Individuals Gene Gene 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 1 1 - - + + - - - - + + + + + + + + - - - - + + 2 2 - - + + - - - - + + + + + + + + + - - - 3 3 - - - - + + - - - - + + - - - - - - - - + + 4 4 - - + + - - + + + + + + + + + + + + - - + + 5 5 - - - - + + + + - - + + - - - - - - - + - 6 6 - - - - + + - - + + + + - - + + - - + + + + Trait Value 0 0 3 3 3 3 2 2 4 4 6 6 3 3 4 4 2 2 1 1 6 5 Number of individuals Trait Value Polygenic traits are Many Gene Traits Positive Allele + increases Trait Value Negative Allele – Decreases Trait Value - +

  3. Individuals Individuals Individuals Individuals Gene Gene 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 Gene Gene 2 2 3 3 4 5 5 6 6 7 7 8 8 11 11 1 1 - - + + - - - - + + + + + + + + - - - - + + 1 1 + + - - + + + + + + + + + + 2 2 - - + + - - - - + + + + + + + + + - - + + 2 2 + + - - + + + + + + + + + + 3 3 - - - - + + - - - - + + - - - - - - - - + + 3 3 - - + + - - + + - - - - + + 4 4 - - + + - - + + + + + + + + + + + + - - + + 4 4 + + - - + + + + + + + + + + 5 5 - - - - + + + + - - + + - - - - - - - + + 5 5 - - + + - - + + - - - - + + 6 6 - - - - + + - - + + + + - - + + - - + + + + 6 6 - - + + + + + + - - + + + + value value 0 0 3 3 3 3 2 2 4 4 6 6 3 3 4 4 2 2 1 1 5 5 value value 3 3 3 3 4 4 6 6 3 3 4 4 5 5 Number of individuals Number of individuals Trait value Trait value Natural Selection on Polygenic traits Natural Selection by death of small individuals Before Natural Selection After Natural Selection Natural selection by death of small individuals

  4. Distribution of a Phenotype in Population BEFORE NATURAL SELECTION 1 Frequency Variance Average 0 Large Small Intermediate Phenotype: Body Size

  5. Distribution of a Phenotype in Population BEFORE NATURAL SELECTION 1 Peak is Average Value Spread around the Peak is Variance Frequency Variance Average 0 Large Small Intermediate Phenotype: Body Size

  6. Distribution of a Phenotype in 2 Populations: Black and Red 1 Peaks are equal: Average = Average Spread around Peaks Are unequal: Variance > Variance Frequency Variance Variance Average Average 0 Large Small Intermediate Phenotype: Body Size

  7. Three kinds of Natural Selection Pink individuals die; Blue individuals live. Directional Selection Stabilizing Selection DisruptiveSelection Before Natural Selection Die Number of individuals Die Die Die 0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125 Body size (g) Body size (g) Body size (g) Selection for small and large individuals Selection for larger individuals Selection for mid-size individuals Two peaks form Peak shifts Peak gets narrower After Natural Selection Number of individuals 0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125 Body size (g) Body size (g) Body size (g)

  8. An Example of Stabilizing Natural Selection • Natural Selection on Larval Body Size in the goldenrod gall fly. • The Ecology involves 5 species: 1. The golden rod gall fly. 2. The golden rod plant. 3. A parasitoid wasp predator. 4. Two avian or bird predators: chicadees and woodpeckers.

  9. All Pictures from Dr. Warren Abrahamson or Paul Heinrich Goldenrod, the ‘host’ plant, Solidago altissima (hexaploid). 130 species of goldenrod in N. America.

  10. Solidago altissima is a clonal plant. That is, a cluster of stems that all belong to the same individual. Each stem is called a ramet and they are connected underground by a ‘root’ called a rhizome. All of the ramets connected to the same rhizome underground and are genetically identical.

  11. Ramets = Stems Solidago altissima is a clonal plant. That is, a cluster of stems that all belong to the same individual. Each stem is called a ramet and they are connected underground by a ‘root’ called a rhizome. All of the ramets connected to the same rhizome underground and are genetically identical. Connected underground

  12. Eurosta solidaginis, goldenrod gall fly Female Male This is the species that is experiencing evolution by Natural Selection. The kind of Natural Selection is Stablizing Selection.

  13. Eurosta solidaginis female ovipositing into a goldenrod ramet. When the fly larva hatches, the maggot’s saliva causes the plant to make a gall. The fly larva will feed on the plant tissue inside the protective gall.

  14. Gall, three weeks after egg. Gall, six weeks after egg.

  15. In Winter: the above-ground Plant dies, But the maggot Lives on inside the gall! Galls or swellings on the ramets of S. altissima. These galls are made by the plant, but are induced by chemicals in the saliva of the goldenrod gall fly maggot.

  16. The adult fly has no chewing mouthparts, so it cannot ‘chew its way out’ of the gall. The fly larva or maggot chews an exit hole in the late fall, when the above-ground plant is dead. When the maggot becomes an adult, it escapes out of the gall through the exit hole. The gall is an imperfect defense for the fly larva.

  17. Why does the fly maggot live inside the gall? The gall is a defense against predators BUT The gall is an imperfect defense for the fly larva.

  18. Eurytoma gigantea, is a parasitoid wasp that preys only on gall fly larvae. This is a female wasp on a green gall getting ready to oviposit her egg into the gall. Her egg will hatch and her larvae will eat the gall fly maggot. Agent of Natural Selection

  19. Because her ovipositor is short, the female wasp attacks the smaller galls. Maggots in the smaller galls are eaten by wasp larvae. Fly larvae in the bigger galls are protected from wasp attack by the thick walls of the gall. Maggot survival strategy: make a BIG gall to escape wasps. ovipositor Agent of Natural Selection

  20. MORE Agents of Natural Selection In the winter, downy woodpeckers and the black capped chickadees eat the gall fly larvae. As many as 60% of all galls are attacked by birds during the winter.

  21. In order to get to the ‘chewy center’ of the gall where the maggot lives, a bird must peck through the protective outer wall of the gall.

  22. The birds seek the largest food reward for their pecking effort and they attack the larger galls. Fly larvae in smaller galls are protected from bird attack.

  23. Maggot survival strategy: make a SMALL gall to escape birds. Note: this is the opposite of the best strategy for escaping wasps!

  24. In order to study Natural Selection acting on gall size, we collect 50 to100 galls from a single field in the early spring, after predation by wasps and birds has occurred. Then, we (1) measure the size of each gall; (2) open each gall and observe its contents (if any); And, (3) Sort the galls into four categories: Live maggot, bird predation, wasp predation, ‘other.’

  25. Typical Data Set

  26. Conclusion: Stabilizing Natural Selection by the combination of predators favors fly larvae which induce intermediate size galls.

  27. Conclusion: Natural selection by predation favors those fly larvae which induce intermediate size galls.

  28. Distribution of Gall Sizes BEFORE NATURAL SELECTION 1 Frequency Variance 20.51 mm 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  29. Distribution of Gall Sizes AFTER NATURAL SELECTION by Wasps 1 Wasp predation on the smaller galls, pushes the mean toward larger size. Natural Selection by wasps favors large gall size: Directional Selection. Average gall size with live Fly is larger. Wasp predation eliminates many of these flies Frequency 20.51 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  30. Wasp Predation Alone High Fitness 1 Low Fitness 20.51 mm 0 Large Small Intermediate Directional Selection: Trait values as one extreme have the Highest Fitness. Trait values at the other extreme have the Lowest Fitness Fly Viability Fitness: Relative Probability of Survival Fly Phenotype: Gall Size in mm

  31. WASP PREDATION and SELECTION Relative Fitness Distribution = SELECTION Relative Fitness: w 1 Fly Phenotype: Gall Size in mm Frequency X multiply two curves Phenotype Frequency Distribution BEFORE SELECTION Fly Phenotype: Gall Size in mm Frequency Phenotype Frequency Distribution AFTER SELECTION Fly Phenotype: Gall Size in mm

  32. Distribution of Gall Sizes AFTER NATURAL SELECTION by Birds Bird predation on the larger galls, pushes the mean toward smaller size. 1 Natural Selection favors small gall size: Directional Selection. Bird predation eliminates many of these flies Frequency 20.51 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  33. Distribution of Gall Sizes AFTER NATURAL SELECTION by Birds Bird predation on the larger galls, pushes the mean toward smaller size. 1 Natural Selection by bird predation favors small gall size: Directional Selection. Frequency 20.51 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  34. Directional Selection: One extreme phenotype has the Highest Fitness. The other extreme has the Lowest Fitness Bird Predation Alone High Fitness 1 Fly Viability Fitness: Relative Probability of Survival Low Fitness 20.51 mm 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  35. BIRD PREDATION and SELECTION Relative Fitness Distribution = SELECTION 1 Relative Fitness: w Fly Phenotype: Gall Size in mm Frequency X multiply two curves Fly Phenotype: Gall Size in mm Phenotype Frequency Distribution BEFORE SELECTION Frequency Phenotype Frequency Distribution AFTER SELECTION Fly Phenotype: Gall Size in mm

  36. Distribution of Gall Sizes AFTER NATURAL SELECTION by Birds AND by Wasps Wasp predation has eliminated many of these flies Bird predation has eliminated many of these flies Frequency Variance Variance 20.51 21.96 Large Small Intermediate Fly Phenotype: Gall Size in mm

  37. Distribution of Relative Fitness in relation to Gall Size High Fitness 1 Fly Viability Fitness: Relative Probability of Survival Low Fitness Variance Low Fitness 20.51 mm 0 Large Small Intermediate Fly Phenotype: Gall Size in mm

  38. 1 Fly Viability Fitness: Relative Probability of Survival Variance 20.51 mm 0 Large Small Intermediate Fly Phenotype: Gall Size in mm Stabilizing Selection: Intermediate phenotypic values have the Highest Fitness, extreme phenotypic values have the Lowest Fitness.

  39. BIRD and WASP PREDATION and SELECTION Relative Fitness: w Fly Phenotype: Gall Size in mm Frequency X multiply two curves Fly Phenotype: Gall Size in mm Phenotype Frequency Distribution BEFORE SELECTION Frequency Phenotype Frequency Distribution AFTER SELECTION Note: Variance is Reduced by Stabilizing Selection Fly Phenotype: Gall Size in mm

  40. Stabilizing Selection on Birth Weight in Humans Mortality at Birth is HIGH For Very Small and For Very Large babies

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