Change Happens: Let’s Deal With It!

1. Change Happens: Let’s Deal With It! A Teachable Unit for Natural Selection Deena Wassenberg and Rob Brooker, University of Minnesota Lianna Etchberger and Greg Podgorski, Utah State University Janet Batzli and Evelyn Howell, University of Wisconsin, Madison Kimberly Hammond, University of California, Riverside Mark Lyford, University of Wyoming, Laramie--Facilitator

8. Unit Sequence Learning Goal Students will understand the relationship between reproductive success and natural selection Outcomes 1 & 2 Outcomes 3 & 4 Outcome 5 ….. Objectives and Overview Introduction to Natural Selection Patterns of Selection Measures of Fitness Pretest CINS Post-Test CINS Form. Assessment 1 Form. Assessment 1 Form. Asses. 3 Form. Asses. 4-6 Formative assessments 1: Pretest - concept inventory for natural selection 2: One-minute paper - misconceptions in evolution 3: Change happens - class activity demonstrating natural selection 4. Clicker question - what form of selection was demonstrated? 5. Clicker questions - natural selection in deer mice 6. Posttest - concept inventory for natural selection Learning outcomes 1: Students will demonstrate that she/he has overcome common misconceptions about natural selection using diagrams and writing. 2. Students will be able to define terms and identify factors that play a role in natural selection. 3. Students will be able to identify patterns of natural selection. 4. Students should be able to quantitatively predict changes in allele or genotype frequencies in a population based on natural selection.. 5. Students should be able to design an experiment to demonstrate the importance of reproductive success associated the natural selection.

9. Concept inventory of natural selection (CINS) Pre-test/Post-testSample question (1/20) How did the different beak types first arise in the Galapagos finches? • The changes in the finches’ beak size and shape occurred because of their need to be able to eat different kinds of food to survive. • Changes in the finches’ beaks occurred by chance, and when there was a good match between beak structure and available food, those birds had more offspring. • The changes in the finches’ beaks occurred because the environment induced the desired genetic changes. • The finches’ beaks changed a little bit in size and shape with each successive generation, some getting larger and some getting smaller. Anderson, D.L., Fisher, K.M., & Norman, G.J. (2002). Development and Evaluation of the Conceptual Inventory of Natural Selection. Journal of Research in Science Teaching, 39, 952-978.http://www.biologylessons.sdsu.edu/CINS6_03.pdf

10. FA: 1 2 3 4 5 6 What is biological evolution?Brainstorm • A heritable change in one or more characteristics of a population or species across many generations Viewed on a small scale relating to changes in a single gene in a population over time (our focus) Viewed on a larger scale relating to formation of new species or groups of species

11. Evolution • Teachable unit flow chart: The flow chart helps us to place our current topic within the larger picture of evolution. Our topic for the next couple of classes will be the relationship between natural selection and reproductive success.

12. FA: 1 2 3 4 5 6 Learning goal • Student will be able to understand that evolution is a heritable change in one or more characteristics of a population or species across many generations

13. Learning exercise • To appreciate the general ideas about natural selection that we might already have coming into this course, let’s begin with a short learning exercise.

14. AAAS 1999 Minute Paper: • Examine cartoon. • Explain the changes that occurred in the tree AND animal using your current understanding of evolution by natural selection. • Individually, write your answer on small card and hand in. • With a partner, list the assumptions being implied in the cartoon.

15. Learning outcome 1: Student will overcome common misconceptions about natural selection using diagrams and writing. Learning outcome 2: Student will be able to define terms and identify factors that play a role in natural selection.

16. FA: 1 2 3 4 5 6 Gene pool • All of the genes in a population • Study genetic variation within the gene pool and how variation changes from one generation to the next • Emphasis is often on variation in alleles between members of a population

17. Population • Group of individuals of the same species that an interbreed with one another

19. FA: 1 2 3 4 5 6 Natural selection in a population We’re going to go through an active learning exercise to appreciate some of the general connections between genetic variation, reproductive success, and natural selection.

20. LOST http://www.youtube.com/watch?v=nsmO2rLxIv0&mode=related&search=

21. Stand-up, sit-down natural selection • 1. Each new generation we all stand up. • 2. Individuals with green eyes, size 8 feet, and short index fingers have children with the same traits. • 3. The population size remains the same each generation.

22. Learning outcome 3: Student should be able to identify different patterns of natural selection.

23. What have we learned? Has this population evolved?

24. Modern description of natural selection 1) Genetic variation arises from random mutations that may alter the function of the protein. 2) Some alleles may encode proteins that enhance an individual’s survival and reproductive success compared to that of other members of the population 3) Individuals with beneficial alleles are more likely to survive and contribute their alleles to the gene pool of the next generation 4) Over the course of many generations, allele frequencies of many different genes may change through natural selection, thereby significantly altering the characteristics of a population • Net result of natural selection is a population that is better adapted to its environment and more successful at reproduction.

25. Some genotypes have greater reproductive success, meaning that they contribute more offspring that are viable to the next generation compared with other genotypes. • Reproductive success depends on: • 1. Ability to survive to reproductive age • 2. Ability to find a mate • 3. Fertility

26. FA: 1 2 3 4 5 6 Natural selection patterns • Directional selection • Stabilizing selection • Disruptive selection • Balancing selection

27. Directional selection • Favors individuals at one extreme of a phenotypic distribution that have greater reproductive success in a particular environment • Initiators • New favored allele introduced • Prolonged environmental change

28. Figure 24.3

29. Stabilizing selection • Favors the survival of individuals with intermediate phenotypes • Extreme values of a trait are selected against • Clutch size • Too many eggs and offspring die due to lack of care and food • Too few eggs does not contribute enough to next generation

30. Figure 24.4

31. Disruptive selection • Favors the survival of two or more different genotypes that produce different phenotypes • Likely to occur in populations that occupy diverse environments • Members of the populations can freely interbreed

32. Figure 24.5

33. Balancing selection • Maintains genetic diversity • Balanced polymorphism • Two or more alleles are kept in balance, and therefore are maintained in a population over the course of many generations • 2 common ways • For a single gene, heterozygote favored • Heterozygote advantage – HS allele • Negative frequency-dependent selection • Rare individuals have a higher fitness

34. Figure 24.6

35. FA: 1 2 3 4 5 6 Clicker question: Our class exercise involved eye color, foot size, and finger length. With regard to changes in index finger length in our population, is this an example of: • Directional selection • Stabilizing selection • Disruptive selection • Balancing selection

36. Sexual selection • Form of natural selection • Directed at certain traits of sexually reproducing species that make it more likely for individuals to find or choose a mate and/or engage in successful mating • In many species, affects male characteristics more intensely than it does female

37. Figure 24.7

38. Explains traits that decrease survival but increase reproductive success • Male guppy (Poecilia reticulata) is brightly colored compared to the female • Females prefer brightly colored males • In places with few predators, the males tend to be brightly colored • In places where predators are abundant, brightly colored males are less plentiful because they are subject to predation • Relative abundance of brightly and dully colored males depends on the balance between sexual selection, which favors bright coloring, and escape from predation, which favors dull coloring

39. Learning outcome 4: Student should be able to quantitatively predict changes in allele or genotype frequencies in a population based on natural selection. Learning outcome 5: Student should be able to design an experiment to demonstrate the importance of reproductive success associated the natural selection.

40. FA: 1 2 3 4 5 6 Quantitative predictions of natural selection • We now turn to natural selection on a quantitative level, which requires that we consider allele frequencies and Darwinian fitness.

41. Allele and genotype frequencies • Related but distinct calculations

42. Darwinian fitness • Relative likelihood that a genotype will contribute to the gene pool of the next generation as compared with other genotypes • Measure of reproductive success • Hypothetical gene with alleles A and a • AA, Aa, aa

43. Suppose average reproductive successes are… • AA  5 offspring • Aa  4 offspring • Aa  1 offspring • Fitness is W and maximum is 1.0 for genotype with highest reproductive ability • Fitness of AA: WAA = 5/5 = 1.0 • Fitness of Aa: WAa = 4/5 = 0.8 • Fitness of aa: Waa = 1/5 = 0.2

44. Mice and hemoglobin • Certain populations of deer mice are found to be polymorphic with regard to a gene that encodes a subunit of the oxygen-carrying protein, hemoglobin • Hh- high altitude allele (high oxygen affinity) • Hl- low altitude allele (low oxygen affinity)

45. Deer Mouse (Peromyscus maniculatus) • Cosmopolitan in North America • Live & breed in harsh conditions across all altitudes (0 - 4000 m) • Gives birth to large litters (4-8 pups) • Genetic polymorphisms in a-globin subunits M.A. Chappell

46. (“Low altitude” allele)

47. FA: 1 2 3 4 5 6 On the next series of slides, you will be asked to use the information from these data to predict changes due to natural selection.

48. Q1. What is the approximate allele frequency for the Hl allele in the mouse population at the red arrow? (Low altitude)

49. Q2. Based on the allele frequency you estimated from question 1, draw a graph that would describe what would happen if the mouse population at the arrow was transported to 4000 m and there were geographic barriers that prevented the population from moving to a lower altitude. 1 0.8 0.6 0.4 0.2 0 Hl allele frequency Generations

50. Q3. Make a curve similar to the one in question 2, but plot the frequency of the Hh allele instead. Q4. Take home assignment. The curves you have drawn in questions 2 and 3 were under the hypothesis that mice carrying the Hh allele have a higher reproductive success at high altitude. Write a paper guided by the rubric available on our web site. Be sure to describe your methods and indicate what type of data you would expect if the hypothesis was correct. The rubric will be used in assessing your work.