Tracing Phylogeny: Macroevolution, the Fossil Record, and Systematics

1. Tracing Phylogeny: Macroevolution, the Fossil Record, and Systematics

2. The Fossil Record and the Geological Time Scale • Fossils are reliable data only if they can be placed in time • relative dating • absolute dating

3. Relative Dating • Younger sediments are found on top of older ones • strata at one location can be related to strata at another location by index fossils • tells us the order in which groups of species present in a sequence of strata evolved • establishes the geological time scale

6. Pangea and Plate Tectonics • Supercontinent • Continental Drift

8. Absolute Dating • Radioactive dating • L and D amino acid content

9. L and D Amino Acid Isomers • Isomers - same formula, different structure • structural • conformational • geometric • stereoisomerism

10. Stereoisomerism • 1815, Jean-Baptistse Biot (physicist) discovered light will interact with molecules in specific ways (Wingrove and Caret 1981) • Pasteur noticed salt residue in wine kegs could be divided into “right-handed” and “left-handed” crystals (Wingrove and Caret 1981) • The crystals were mirror images of each other.

11. Mirror Images • To understand mirror images, place left hand down on table. Imagine a mirror next to it. The mirror image of the left hand is the right hand. • Try to superimpose left hand over right and see if the thumbs line up. • Your hands are non-superimposable

12. Dextrorotatory vs Levorotatory • When Pasteur dissolved left-handed crystals in water, plane polarized light is bent to the left • Right handed crystals bend plane polarized light to the right

13. Horizontal & vertical waves Only vertical component comes through polarizer

14. Bends light to the right Right-handed crystals in solution

15. By using a device to measure the angle of the rotation, the magnitude of rotation can be determined. • Light bent to the right is called dextrorotatory (d) • light bent to the left is called levorotatory (l) • When you mix equal quantities of “d” and “l” crystals, there is not net rotation (they cancel each other out).

16. Enantiomers • Molecules that exhibit optical activity and are nonsuperimposable mirror images are said to be enantiomers • Enantiomers are molecules with same formulas that the structures are (1) mirror images and (2) must not be superimposable on the other.

17. MIRROR

18. Racemic Mixtures • Equal amounts of “d” and “l” means no optical activity • This is a racemic mixture • However, nature doesn’t always produce equal amounts • Life produces only l-amino acids • When an organism dies, “l” forms are converted into a mixture of “l” and “d” • Ratio of “l” and “d” can be used to date by racemation

19. D-leucine L-leucine

20. Radioactive Dating and Half-Life • Radioactivity discovered by Henri Becquerel • some elements i.e. uranium and thorium are unstable • they decay to form other elements or isotopes of the same element • alpha particles • beta particles • gamma rays

21. Alpha Particle • Nucleus of a helium atom (or two protons and two neutrons) emitted in nuclear disintegration + + + + Tracks made over period of 48 hours by alpha particles emitted from a radioactive particle of plutonium in lung tissue of ape. (http://ccnr.org/alpha_in lung.html)

22. Beta Particle • Formed when a neutron splits into a proton and an electron in the nucleus

23. Gamma Rays • High energy photon (light) emission in radioactive disintegration

24. Uranium Decay 238 92 • U has 92 protons and 146 neutrons • unstable at 238 and so emits an alpha particle • dropping two protons and two neutrons from U nucleus now makes it Thorium (daughter element) with a mass of 234 • 238U ----->234Th + 4He92 90 2 • Thorium is unstable and emits a beta particle

25. Beta Decay • A beta particle is formed when a neutron splits into a proton and an electron in the nucleus • There is now an extra proton in the nucleus to form the element Protactinium 234Pa91 • As alpha, beta and gamma rays are emitted to the surrounding materials, they heat up

26. Rate nuclear adjustments occur to form lead is independent of changes in: • temperature • pressure • chemical environment • rate of decay of long-lived isotopes has not varied since earth came into existence • each radioactive element has a particular mode of decay and unique rate of decay • radiometric dating makes use of the rate of decay and mode of decay

27. Time “zero” begins when radioactive parent atoms become part of mineral from which daughter elements cannot escape • retention of daughter elements essential - must be counted to determine original quantity of parent nucleotide • ratio of parent to daughter nucleotide is by mass spectrometer (Geiger used for Carbon 14)

28. Igneous rocks date best • sedimentary rocks rarely can be dated (only certain crystalline forms in rocks) • metamorphic rocks require special care also

29. Problems with Radiometric Dating • Weathering of rock or leaching of minerals cause underestimation of age • if material is gas, may diffuse out of rock • older rocks may partially re-melt so age taken would be of second rock formation

30. Half-Life • Number of years needed for half of the original quantity of atoms to decay to its stable form • every radionucleotide has its own unique half-life • 235U = 704 million years

31. Some Half-Lives

32. Potassium-Argon Method • Occurs by electron capture (causes proton to be transformed into neutron) • 11% of potassium changes to argon • rest of potassium decays to 40Ca by beta emission (not useful) • advantage is argon is inert • another advantage is abundance of K in minerals

33. Rubidium-Strontium Method • Beta decay of 87Rubidium to 87Strontium • Rubidium and potassium often found in same minerals, therefore, can use to check K dating • Measure: • 87Rubidium • 87Strontium • 86Strontium • Ratios of each against each other via mass spectrometer

34. 14Carbon Method • Organic substances older than 50,000 years contain little 14C • 14C is continuously made (cosmic radiation) • when living organism quits assimilating carbon, addition of 14C stops • decays to 14N by beta emission • age determined by ratio of 14C to all other C in organism

35. Thorium Decay • Uranium brought to ocean by streams (in solution) • decays to from 230Th • 230Th precipitated as sediment on the ocean floor • half-life = 75,000 years

36. How Do New Designs for Living Evolve? • Predaptation • most biological structures have an evolutionary plasticity that makes alternative function possible • a structure evolves in one context and becomes used for another (bird’s wings)

37. Designs for Living • Developmental rates • allometric growth • differences in the relative rates of growth of various parts of the body • gene mutation?

38. Designs for Living • Developmental rates • timing of development • paedomorphism • when adults retain features that are juvenile • heterochrony • evolutionary changes in the timing or rate of development • homeotic changes • alter placement of different body parts

39. Taxonomy • Kingdom • Phylum • Class • Order • Family • Genus • Species

40. Binomial Nomenclature • Taxon • monophyletic • single ancestor gives rise to all species • polyphyletic • species derived from 2 or more ancestral forms not common to all members • paraphyletic • excludes species that share a common ancestor that gives rise to species included in the taxon

41. Molecular Systematics • Protein comparison • DNA comparison • Molecular clocks, i.e. cytochrome c evolution is quite constant with time.

43. Plains zebra (Equus burchelli) - wider and fewer - devlop 3 weeks after fertilization in embryo. Grevy’s zebra (Equus grevyi) more numerous, narrower - develop 5 weeks after fertilization

44. Axolotl