Understanding Evolutionary Theory and Natural Selection

1. Chapters15-17 Evolution

2. Science Definitions

3. Theory Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html A well-substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws and successfully verified hypotheses.

4. Evolution • Book definition = Gradual accumulation of adaptations over time. • In genetic terms, the change in the frequency of alleles in populations from generation to generation. (change over time) Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html

5. Adaptation Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html Any heritable characteristic (determined from alleles) of an organism that improves its ability to survive and reproduce in its environment. Note: not all characteristics are adaptive

6. Adaptations http://animals.nationalgeographic.com/

7. Fitness Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html The success of an individual in surviving and reproducing, measured by that individual’s genetic contribution to subsequent generations.

8. Natural Selection • Charles Darwin’s Theory • Mechanism for change in populations. • Occurs when organisms with certain traits survive, reproduce and pass their variations to the next generation. • “Survival of the Fittest”

9. Natural Selection 1. Variations exist in a population

10. Natural Selection Sweet! I’m better at surviving because I blend into my surroundings! Dang! 2. Some variations improve the ability to survive and reproduce in the particular environment

11. Natural Selection Dang! I have more fitness than you! 3. The individuals with the adaptive traits are more likely to pass on their genes to future generations

12. Natural Selection 4. Over time, the frequency of adaptive alleles increases = evolution.

13. Tenants of Natural Selection • OVERPRODUCTION: Organisms produce more offspring than their environment can support. • HERITABLE VARIATION: Offspring vary in their appearance and function; some of these variations are heritable. • COMPETITION: Offspring must compete for survival, food and reproduction. *SURVIVAL OF THE FITTEST: Offspring who have the highest fitness for their environment will live longer and/or leave more offspring than those less suited for the environment.

14. Can we see natural selection in one generation? • No… • This process occurs very slowly, over many generations • Natural selection can only be observed as changes in the characteristics or behaviors in populations over time.

15. Is there any variation in pinto beans???

16. Bean Variation Mini-Lab • Create Data Table with two three columns: Bean Number, Mass (g), and Qualitative Observations • Work with a partner and choose 10 random beans from the beakers at your station. Try not to be selective for any properties whatsoever • Measure each bean’s mass and record, along with qualitative observations • Share your data with two other groups to get a total of 30 beans recorded.

17. Bean Variation Mini-Lab • In your journal, create a frequency distribution graph as modeled on the whiteboard. For the x-axis, use bean mass (g), and put number of beans on the y-axis Answer the following questions in your journal: • How does your graph compare to the overall class data? • What factors do you think are responsible for causing the variation in the pinto beans? • What could be advantages of being bigger or smaller for a bean seed? Identify several.

18. Natural Selection… Caterpillars… what is the benefit of looking like bird poop?

19. Overproduction & Heritable Variation in butterflies… • How many offspring do butterflies produce? • 1000+ offspring … not that many survive • What kind of variation could we see in larva (caterpillars)? • Different color patterns • Different sizes • Diet • Is this variation in color patterns heritable? • Genes control color patterns in all organisms… • Offspring from a butterfly (caterpillar) that was green as a larva? • Offspring from a butterfly (caterpillar) that was brown and white as a larva?

20. Competition & Survival of the Fittest… • Caterpillars have competition for food, survival & reproduction. • Who will survive the longest? • Best camouflage = less likely to be seen by predators = longer survival = more reproduction • If those that look like bird poop survive longer, what will the population start to look like over many generations? • Like bird poop! • NATURAL SELECTION – the natural selection of characteristics that allow an animal to survive and reproduce (sometimes because of their ability to blend in with their environment)– makes them more fit.

21. Other examples of selection for survival…

22. Natural Selection… Cheetahs… why can they run so fast?

23. Overproduction & Heritable Variation in cheetahs… • How many offspring do cheetahs produce? • 5-6 offspring per year … not that many survive • What kind of variation could we see in cheetahs? • Size of the heart • Length of the legs • Color patterns • + many others • Is this variation in length of legs heritable? • Genes control length of limbs … • Offspring from a cheetah with long legs? • Offspring from a cheetah with short legs?

24. Competition & Survival of the Fittest… • Cheetahs have competition for food, survival & reproduction. • Who will survive the longest? • Those that can run fast enough to catch prey to survive = longer survival = more reproduction. • If those that run faster eat more, what will the population start to look like over many generations? • Fast runners! • NATURAL SELECTION – the natural selection of characteristics that allow an animal to get more food within their environment – makes them more fit.

25. Sexual Selection… The male peacock… why waste so much energy producing feathers?

26. Overproduction & Heritable Variation in peacocks • How many offspring do they produce? • 6-8 per year are hatched… not that many survive • What kind of variation could we see in male peacocks? • Different color patterns • Different feather sizes • Size of bird • Is this variation in feather size heritable? • Genes control how large feathers will get… • Offspring from a peacock with large feathers? • Offspring from a peacock with short feathers?

27. Competition & Survival of the Fittest… • Peacocks have competition for food, survival & reproduction. • Who will reproduce the most? • Largest feathers = more reproduction • If those with large feathers reproduce more, what will the population start to look like over many generations? • Larger feathers, on average. • SEXUAL SELECTION – the natural selection of secondary sex characterizes in males is WORTH the energy they spend because it increases levels of reproduction – makes them more fit.

28. Other interesting secondary sex characteristics….

29. Natural Selection in recent years…

30. Bt-resistant Cotton Bollworm

31. Antibiotic Resistance

32. AZT-Resistant HIV (AIDS virus)

33. AZT-Resistant HIV (AIDS virus) Resistance to AZT has evolved in all patients taking the drug (usually in ~6 months)! How does HIV evolve so rapidly? 1. High mutation rate • HIV’s mutation rate is 106 higher than ours! 2. Short generation time • 1 year ≅ 300 viral generations. 10 years of viral ≅ 2-3 x 106 years of human evolution!

34. Natural Selection ? Over the past few weeks we did a lab demonstrating natural selection… you just didn’t know about it.

35. What is a species? A group of interbreeding populations that cannot breed with other groups. Giraffes and Elephants? German Shepards and Poodles?

36. Speciation Hurricane http://evolution.berkeley.edu

37. Speciation The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection. http://evolution.berkeley.edu

38. Speciation So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they’ve evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations. http://evolution.berkeley.edu

39. Speciation Because of “geographic” isolation, “maltose flies” preferred other “maltose flies,” and “starch flies” preferred other “starch flies” when choosing mates

40. Speciation One species splits into two due to isolation (geographic, reproductive, etc…) Also known as Divergent Evolution… results in homologous structures between groups

41. Speciation http://evolution.berkeley.edu

42. Direction of Natural Selection and Species Formation • Stabilizing – extremes not favored (example – human birth weight) • Disruptive – extremes favored (example - short or long beaks not medium beaks) • Directional – extremes at one end favored

43. Isolation • Geographic Isolation: separated by a physical barrier of some kind • Behavioral Isolation: Differences in courtship displays prevent reproduction • Temporal Isolation: separated by differences in the timing of reproduction

44. Genetic Drift • Random changes in numbers of individuals in a population can lead to allele frequency changes in a population • This is called Genetic Drift

45. Assignment #1 • Complete the following chart using pages 398 & 399

46. Assignment #2 • Complete the following chart using pages 404 & 405

47. Phylogeny Figure 1: A diagram of Mimi's immediate family. The passage of genes from parents to offspring is indicated by the green lines.

48. Figure 2: The genetic relationships for the last three generations of beetles under Mimi's log.

49. Figure 3: Genetic relationships for a segment of Mimi's beetle population over a number of generations. The last three generations of beetles under Mimi's log are shown in the blue frame.

50. Figure 4: Genetic relationships between two closely related species, Bembidion levettei and Bembidion zephyrum. Recent generations of beetles in Mimi's species are indicated with the blue frame. The arrow points to the common ancestor of the two beetle species.