Understanding Genetic Variation and Evolution: Agents of Change, Natural Selection, and Adaptation

1. Genetic variation and Evolution • Chapter 20 • Why are organisms well adapted to their habitats? • Creationist explanation (see section 21.7) • Is a religious view • Divine role • “intelligent design” • not scientifically testable • Scientific explanation • “evolution from common ancestor” • ‘Natural Selection” • -- is testable 20.2 -- should know H-W equation and why it’s important -- we may come back to this 20.4 – understand the meaning of fitness, but we’ll not cover the mathematical aspects 20.5 – skip 20.6 – read on your own 20.8 – read on your own Genetic Variation & Evolution

2. Darwin was not first to describe evolution George Cuvier (1790) – Fossils & ‘Catastrophism’ Jean Lamarck (1809) -- Environmental influence Lamarck’s theory of “Inheritance of Acquired Traits” Genetic Variation & Evolution

3. Modern explanations of why traits change over time (20.3) Why do the traits of a species change over time 5 Agents (mechanisms) of change: 1. Genetic Mutation– random changes to DNA code -- is the ultimate source of all new traits traits -- creates variation within a piopulation -- ‘raw material’ of all evolutionary mechanisms 2. Natural selection– mechanism proposed by Darwin -- environment selects certain traits Genetic Variation & Evolution

4. Gene Flow Founder effect Bottleneck effect Agents of change, con’t Other agents of change 3. Gene flow -- movement of individuals between populations 4. Nonrandom mating -- organisms prefer to mate with certain individuals 5. Genetic drift -- random variation in the distribution of traits from one generation to the next. Extreme examples Founder effect – population isolation bottleneck effect – population catastrophe -- gene pool reduction Animation Genetic Variation & Evolution

5. What are the fundamental premises of • Darwin’s theory of “Natural Selection”? • Read Section about Evolution in Chapter 1 • “On the Origin of Species by Means of Natural Selection” • “Evolution” (a process) • does not equal “Natural Selection” (a process) • Natural selection occurs when: • 1) There exists genetically based variation (inheritable) • in the traits of a species. • 2) Organisms produce more offspring than can survive. • 3) The environment selects for those organisms • with the best adapted traits. • -- i.e., interactions with other organisms & habitat • 4) Organisms best adapted to the environment will reproduce most successfully. Genetic Variation & Evolution

6. There is variation in all traits of all species What is nature of genetic variation? = a range of forms Why? Genetic mutation DNA Polymorphisms -- SNPs Different ‘alleles’ The environment selects among but does not create variations! Genetic variation in Asiatic lady beetle Genetic Variation & Evolution

7. Do organisms always produce more offspring than can survive? Cichlides: Carmagnola Grey rabbit: Humans: 250,000 eggs 5-8 litters x 7 offspring 2- 7 children/family Genetic Variation & Evolution

8. How does Darwin’s ‘Natural Selection’ explain giraffe evolution? Unlike Lamarcke, traits must be genetically determined The environment creates “Selective Pressures” Which select for best adapted traits An “Adaptation” = a trait selected for by the environment Genetic Variation & Evolution

9. What are examples of environmental selective pressures? • Predator-prey interactions • Competition for resources • Habitat changes!! (Natural or anthropgenic • Natural selection acts upon existing genetic variation • -- theory is not ‘teleological” • -- no purpose, plan, or intent • Wrong: • “In order to hide from predators, the dead-leaf • butterfly evolved a leaf-like appearance.” • “The dead-leaf butterfly wanted to be better • camouflaged and evolved a leaf-like appearance.” • “Butterflies mutated because of predation and began • To look more like a dead leaf.” • Correct: • “Predation selected for butterflies that most • resembled a dead leaf.” • l Genetic Variation & Evolution

10. What are the effects of Natural Selection on a population? (20.7) “Microevolution” vs “Macorevolution” Genetic Variation & Evolution

11. What is the effect of Directional Selection on a population? Progressive change in a trait within a species Genetic Variation & Evolution

12. How does Disruptive Selection affect a population? Responsible for divergence of a single species into two different species Modern example of process: blackbellied seedcracker Genetic Variation & Evolution

13. How does Stabilizing Selection affect a population? Human birth weight & Eurosta gall size Stabilizing selection & ‘living fossils’ Genetic Variation & Evolution

14. All these crops are varieties of the species Brassica napa What is ‘Artificial Selection’? Colors represent different genetic types. Map shows genetic variation in Africa. Genetic Variation & Evolution

15. Why can artificial selection cause genetic problems? -- in breeding -- founder effect -- harmful recessive traits speciesnon-inbred inbred Zebra lived 20 3 died 7 2 Eld’s deer lived 13 0 died 4 7 Giraffe lived 11 2 died 3 3 Oryx lived 35 0 died 2 5 Dorcas lived 36 17 gazelle died 14 25 From Klug & Cumminings Genetics 5th ed Genetic Variation & Evolution

16. Why won’t humans evolve wings? Limits of Selection Existence of genetic variation Complex traits involve many genes Suitable selective pressures Genes have multiple effects -- developmental genes Are humans still evolving? Genetic Variation & Evolution

17. What is the evidence for evolution? (Chapter 21) • Observations of evolution • Paleontology & Fossil records • Anatomic evidence • Molecular evidence Evolution II

18. Observations of evolution Peppered moths -- Industrial melanism -- and its reversal Evolution II

19. Other Examples Wheat ( ~ 9 K yrs ) Banana moths in Hawaii (1000 yrs) Faroe Island house mouse (250 yrs) Copapod of the Salton Sea, CA (30 yrs) Drosophila paulistorum (a few yrs in a lab) Evolution II

20. Ambulocetus natans (c. 50 Ma) – which means "walking whale that swims Paleontology What does the fossil record show? Extinct life forms Sequential appearance of derived characteristics Transitional forms What are some limitations of the fossil record? Habitat Geologic disruption Soft-bodied organisms Evolution II

21. How are fossils dated? Principle of “superposition” -- relative dating Radioisotope dating (absolute dating) half-life 14C  14N -- 5,730 years (useful to ~ 60K yrs BP) 234U  230TH, ~ 80,000 years 40K  40Ar ~ 1.3 Billion yrs Evolution II

22. Anatomical evidence What type of evidence does anatomy reveal? Derived traits have similar anatomy “homologous structures” But “Convergent evolution’ occurs independent evolution “analogous structures” Why does this occur? Distinguishing homologous and analogous traits is not always easy A platypus has fur, a bill, webbed feet, and lays eggs Evolution II

23. Anatomical Evidence, con’t. What does this mean: “Ontogeny reciprocates Phylogeny”? Ernst Haekel’s original data is somewhat flawed What are vestigial structures? What are vestigial genes? -- gene for stripes in horses -- genes for teeth in birds See Wikipedia for other cool examples http://en.wikipedia.org/wiki/Vestigial Human coccyx Evolution II

24. Anatomical Evidence, con’t. Intelligent design – not! Human pelvis External Testis Eye? Why? Human coccyx Evolution II

25. Molecular Evidence Comparison of DNA (base) and protein (amino acid) sequences DNA base sequence codes for protein amino acid sequence Changes in DNA sequences can be used as a Molecular Clock -- need to know rate of mutation -- can estimate when two species diverged From a common ancestor Cytochrome-c base substitutions Evolution II

26. Chapter 26 and 22: Biological Classification and the Nature of Species Biological classification system: Domain Kingdom Phylum Class Order Family Genus Species Carolus Linnaeus developed system for classifying life and giving each a unique name We know include “Domains” Evolution II

27. Scientific naming of species Scientific binomial – Carolus Linnaeus Genus + Species Homo sapiens vs “humans” Acer rubrum vs “red maple” Writing Conventions Biological classification system: Domain Kingdom Phylum Class Order Family Genus Species So, what is a species?? “A group of interbreeding organisms that are reproductively isolated” What is ‘reproductive isolation’? Which of these is Acer rubrum? Evolution II

28. What are some mechanisms of reproductive isolation? Pre-zygotic Ecological (habitat) e.g., mountain ranges Mechanical e.g. reproductive anatomy Temporal e.g. mating seasons Behavioral e.g., mating rituals Gametic gametes incompatible (many plants) e.g., frogs of Sierra Nevada foothills e.g., bowerbirds of Australia Bowerbirds Evolution II

29. Mechanisms of reproductive isolation, con’t. Post-zygotic Hybrid inviability -- embryo / fetus does not develop e.g., cattle and water buffalo Hybrid infertility -- offspring is infertile e.g., colored and pied flycatchers Meet and hybridize in central and northern Europe Question Evolution II

30. The biological species concept has limitations If two species can hybridize, are they separate species? -- plants -- animals Should all dogs be classified in the same species? Native: California Tiger Salamander Invasive: Adult Barred Tiger Salamander Hybrid: Appears to be more fit then native http://sciencemode.com/2007/09/20/california-barred-tiger-salamanders-interbreed-produce-hybrids/ Evolution II

31. How does geographic distribution relate to speciation? Allopatric speciation: Original species is split by geographic isolation -- mountains, rivers, islands Different species remain after barrier is gone How does Sympatric speciation occur? e.g., “blackbellied seedcracker” Environment selects for 2 different forms A less fit hybrid “reinforces” divergence Question Evolution II

32. Temporal isolation explains origin of the apple maggot Apple Maggot Hawthorn Visit Martin G. Kelly’s site at http://www.sciencecases.org/maggot_fly/maggot_fly.asp Apple Evolution II

33. Under what conditions does ‘Adaptive Radiation’ occur? • A special case of disruptive evolution Darwin’s Finches -- classic example Can occur regionally or globally -- rise of mammals Adaptations reinforced by “Character Displacement’ Question Evolution II

34. Plotting macroevolution What are some characteristics of evolution that can be diagrammed? Gradualism vs ‘punctuated equilibrium’ Stephen J Gould & Niles Eldredge What are possible mechanisms of rapid speciation? -- polyploidy -- mutations to developmental genes -- geologic time vs ‘human’ time Evolution II

35. Plotting evolutionary relationships (from Chapter 23) The traditional “evolutionary tree” vs Claudistics Clade= all organisms with “Shared derived characteristics” Evolution II

36. Highlights of the History of Life (from Chapter 26) Advanced life forms have appeared Late in earth’s geologic history Origin of life ~ 3.8 bya Eukaryotic cells ~ 1.7 bya Multicellular organisms ~ 1.2 bya Humans only ~ 1 mya Origin of life Multicellular organisms Evolution II

37. The origin of major groups of animals The ‘eras’ The Cambrian explosion Vertebrates Invertebrates Age of reptiles Age of mammals Insects most successful of them all Evolution II

38. There have been many mass extinctions! Some small, Some BIG! Question Evolution II