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Lecture 2 : Evolutionary Patterns, Rates And Trends


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Lecture 2 : Evolutionary Patterns, Rates And Trends

  2. 3. Key Concepts <ul><li>Evidence of Evolution </li></ul><ul><li>- comes from biogeography, fossils and comparisons of body form, development and biochemistry among major groups. </li></ul>
  3. 4. Macroevolutionary Events <ul><li>Asteroid impacts, changing climates and other global events contributed to the mass extinctions and recoveries, as well as emergence of new species. </li></ul>
  4. 5. Organization of Evidence <ul><li>Naming and classifying species helps us to manage data on biodiversity. </li></ul><ul><li>Cladistics is an evolutionary classification system that groups species with respect to derived traits that evolved only once, in their last shared ancestor. </li></ul>
  5. 6. Evidence from biogeography <ul><li>Theory of uniformity prevailed when the geologists map out vertical stacks of sedimentary rock. </li></ul><ul><li>Recurring geologic events and others had changed the Earth irreversibly. </li></ul><ul><li>`Jigsaw puzzle’ of Africa with the Atlantic coasts of South America? </li></ul><ul><li>Were all continents once part of a bigger one that had splits into fragments and drifted apart? </li></ul>
  6. 7. Evidence from biogeography <ul><li>Findings as put continential drift into a broader explanation of Earth’s crustal movements, the plate tectonics theory. </li></ul><ul><li>A big connection  huge land on collision courses. Masses converged to form supercontinents that split forming new ocean basins  Gondwana drifted south from the tropics until crunched into other land masses. </li></ul>
  7. 8. Continental Drift <ul><li>Continents were once joined and have since “drifted” apart </li></ul><ul><li>Initially based on shapes </li></ul><ul><li>Later supported by world distribution of fossils and existing species, orientation of particles in iron-rich rocks </li></ul>
  8. 9. Plate Tectonics <ul><li>Earth’s crust is fractured into plates </li></ul>
  9. 10. island arc oceanic crust oceanic ridge trench continental crust subducting plate athenosphere (plastic layer of mantle) hot spot lithosphere (solid layer of mantle) Fig. 13-6a, p.199 Plate Tectonics <ul><li>Movement of plates is driven by upwelling of molten rock at mid-oceanic ridges </li></ul>
  10. 11. Evidence from biogeography <ul><li>The new supercontinent, Pangea extended from pole to pole. With erosive forces of water and wind resculpted the land. </li></ul><ul><li>Asteroid and meteorites hit the crust which left impacts and long term effect on the global temperature and climate. </li></ul><ul><li>Such changes on land and in the ocean and at atmosphere influenced life’s evolution which took off in a new direction. </li></ul>
  11. 12. Asteroid Impacts <ul><li>Many past catastrophic impacts altered the course of evolution </li></ul><ul><li>Iridium layer implicates asteroid in extinction of dinosaurs </li></ul><ul><li>Asteroids are still a threat </li></ul>
  12. 13. 10 mya 65 mya 260 mya 420 mya where ( seed fern) and Lystrosaurus (a tusked herbivore) evolved 420 mya – early supercontinent Gondwana 260 mya- collision of land masses Forming Pangea 65 mya – Pangea split apart and fragments drifted apart 10 mya – the present position
  13. 14. Life in Pangea 260 mya <ul><li>Glossopteris (Seed fern) </li></ul><ul><li>Lystrosaurus (a Therapsid </li></ul><ul><li>tusked herbivore) evolved </li></ul>
  14. 15. Evidence from Fossils <ul><li>Physical evidence of organisms that lived in the distant past. </li></ul><ul><li>Stratified layers of sedimentary rock are rich in fossils are historical record of life. </li></ul><ul><li>The deepest layers generally contain the oldest fossils. </li></ul>
  15. 16. Fossils <ul><li>Recognizable evidence of ancient life </li></ul>
  16. 17. What do Fossils Tell Us? <ul><li>Each species is a mosaic of ancestral and novel traits </li></ul><ul><li>All species that ever evolved are related to one another by way of descent </li></ul>
  17. 18. Stratification <ul><li>Fossils are found in sedimentary rock </li></ul><ul><li>This type of rock is formed in layers </li></ul><ul><li>In general, layers closest to the top were formed most recently </li></ul>
  18. 19. Sedimentary Rock
  19. 20. Record Is Incomplete <ul><li>Fossils have been found for about 250,000 species </li></ul><ul><li>Most species weren’t preserved </li></ul><ul><li>Record is biased toward the most accessible regions </li></ul><ul><li>Even so, the fossil records is substantial enough to reconstruct patterns and trends in the history of life. </li></ul>
  20. 21. Dating Pieces of the Puzzle <ul><li>How do we assign fossils to a place of time? </li></ul><ul><li>How do we know how old they really are? </li></ul><ul><li>By using the radiometric dating, this is possible. </li></ul><ul><li>Understand the nature of radioisotope decay. </li></ul><ul><li>A radioisotope is an atom of an element with an unstable nucleus which decays spontaneously until the atom becomes a more stable element. </li></ul>
  21. 22. Radiometric Dating <ul><li>The proportions of the radioisotope to its daughter elements in a sample can be used to calculate the sample’s age. </li></ul><ul><li>This applies when the rate of decay for each isotope is constant. </li></ul><ul><li>A predictable number of a radioisotope’s atoms in any sample will decay in a characteristic time span. </li></ul><ul><li>No change in pressure, temperature or chemical state alters that rate. </li></ul>
  22. 23. Radiometric Dating <ul><li>Can be used to reveal the age of rocks. </li></ul><ul><li>E.g. with uranium 238-to-lead ratio in the oldest rocks, geologists predicted that the Earth formed more than 4.6 billion years ago. </li></ul><ul><li>Dating the sedimentary rock yield s the date its component materials formed but not the date they actually sedimented. </li></ul><ul><li>The only way to date the old fossils is to find their position relative to the rocks. </li></ul>
  23. 24. Radiometric dating <ul><li>Fossils that retain some carbon can be dated directly by measuring their ratio of 12 C to 14 C. </li></ul><ul><li>Trace amounts of 14 C were incorporated in the tissues of a living mollusk. </li></ul><ul><li>As long the mollusk was living, the proportion of 14 C to 12 C remained the same in the tissue. </li></ul>
  24. 25. Radiometric dating <ul><li>When mollusk died, it stopped gaining carbon. </li></ul><ul><li>Over time, the proportion of 14 C to 12 C in its remain fell due to the radioactive decay of the 14 C. </li></ul><ul><li>Half of the 14 C had decayed in 5,370 years. </li></ul>
  25. 26. Radiometric dating <ul><li>When such fossil is found and measured of its 14 C to 12 C ratio to determine the half-life reductions since death. </li></ul><ul><li>The ratio turns out to be one eighth of the 14 C to 12 C ratio in living organisms. </li></ul><ul><li>Thus, the mollusk lived about 16,000 years ago. </li></ul>
  26. 27. Radiometric Dating <ul><li>Organism becomes buried in ash or sediments </li></ul><ul><li>Organic remains become infused with metal and mineral ions </li></ul><ul><li>Carbon 14 dating </li></ul>
  27. 28. Radiometric Dating after two half-lives after one half-life parent isotope in newly formed rock
  28. 29. <ul><li>The decay if radioisotopes at a fixed rate to more stable forms. </li></ul><ul><li>The half –life of each kind of radioisotope is the time it takes for 50% of a sample to decay. </li></ul><ul><li>After two half-lives, 75% of the sample has decayed , and so on. </li></ul>
  29. 30. Geologic Time Scale <ul><li>Boundaries based on transitions in fossil record </li></ul>Cambrian period Proterozoic eon 2,500 mya Archean eon and earlier Ordovician period Silurian period Devonian period 544 505 440 410 Carboniferous period Permian period Cretaceous period Tertiary period Quaternary period 360 286 248 213 145 65 Cambrian period Jurassic period Triassic period Paleozoic era Mesozoic era Cenozoic era Phanerozoic eon
  30. 31. Macroevolution <ul><li>Major patterns and trends among lineages </li></ul><ul><li>Rates of change in geologic time </li></ul>
  31. 32. 5:28:41 A.M., origin of eukaryotes 2:05:13 A.M. origin of prokaryotes 11:59:59 A.M. , first humans 11:44:30 A.M. , dinosaurs, flowering plants Earth’s crust solidifies Fig. 13-5, p.198 11:21:10 A.M. , origin of mammals 10:51:7 A.M. , early fishes Macroevolution
  32. 33. Evidence from Comparative Morphology <ul><li>Evolution mans heritable changes in lines of descent. </li></ul><ul><li>Comparisons of body form and structures of major groups of organisms yield clues for the evolutionary relationships. </li></ul><ul><li>Comparative morphology is study of body forms and structures of major groups of organisms. </li></ul>
  33. 34. Comparative Morphology <ul><li>Evidence of a common ancestor maybe due to the similarities in the internal structure of one or more body parts. </li></ul><ul><li>Similar body parts which reflect shared ancestry are homologous structures. </li></ul><ul><li> used differently in different groups, but same genes direct their development. </li></ul>
  34. 35. Morphological Divergence <ul><li>Population of a species diverge genetically after gene flow ends between them. </li></ul><ul><li>Over time, some of the traits that define the species also diverge. </li></ul><ul><li>Change from body form of a common ancestor is a macroevolutionary pattern. </li></ul>
  35. 36. Morphological Divergence <ul><li>Change from body form of a common ancestor </li></ul><ul><li>Produces homologous structures </li></ul>1 1 1 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 4 4 4 4 4 5 5 5 5 early reptile pterosaur chicken bat porpoise penguin human
  36. 37. Morphological Convergence <ul><li>Similar body parts are not always homologous and may have evolved independently in separate lineages as adaptations to the same environmental pressures. </li></ul><ul><li>Such parts are named as analogous structures which look alike in different lineages but did not evolve in a shared ancestor. </li></ul><ul><li>Evolved independently after lineages diverged. </li></ul><ul><li>Evolution of similar body parts in different lineages is called morphological convergence. </li></ul>
  37. 38. Morphological Convergence
  38. 39. body wall (exoskeleton) strong membrane (extension of wall) wing veins Fig. 13-9c2, p.202 Morphological Convergence
  39. 40. Limbs with 5 digits wings birds crocodiles Humans bats Insects wings wings The evolutionary tree diagram shows that wings evolved independently in three separate lineages that bled to bats, birds and insects.
  40. 41. Key concepts <ul><li>With morphological divergence , a body inherited from a common ancestor becomes modified differently in different lines of ancestor. Such parts are homologous structures. </li></ul><ul><li>With mophological convergence , body parts appear alike evolved independently in different lineages, not in a common ancestor. Such parts are analogous structures. </li></ul>
  41. 42. Changes in patterns in development <ul><li>Comparing the patterns of embryonic development often yields evidence of evolutionary relationships </li></ul><ul><li>Similarities in patterns of development are often clues to shared ancestry. </li></ul><ul><li>Mutation in master genes are capable of launching body plans in new evolutionary directions. Changes in these and other genes that affect development may result in structural differences among related lineages. </li></ul>
  42. 43. Genes and variation <ul><li>Homoetic genes guide formation of specific body parts during embryonic development. </li></ul><ul><li>A mutation in one homoetic hgene can disrupt the body’s form. </li></ul><ul><li>Consequences, may be severe or maybe advantageous. </li></ul><ul><li>e.g. formation of flowers. </li></ul>
  43. 44. Genes and Variation <ul><li>How many legs? </li></ul><ul><li>Impact of mutations on animal evolution. </li></ul><ul><li>Embryos of many vertebrate species develop in similar ways. </li></ul><ul><li>Heritable changes in the onset, rate or completion of early steps in development occur. </li></ul>
  44. 45. How many legs? <ul><li>Mutations in master genes may explain why animals differ in the number of appendages. </li></ul><ul><li>Dlx , a homoetic gene makes limbs from wherever is expressed. </li></ul><ul><li>Fossil animal  unrestricted expression of Dlx gene in Cambrian times. </li></ul>
  45. 46. <ul><li>Variations in control over Dlx expression, showed by green fluorescence in embryonic appendages of </li></ul><ul><li>velvet walking worm </li></ul>Blue dye in mouse embryo’s foot
  46. 47. Chimps and Humans <ul><li>Gene duplications may account for some major functional differences among species that have nearly identical genes. </li></ul><ul><li>Last shared ancestor of chimpanzees and humans lived between 6-4 mya. </li></ul><ul><li>Not more than 98% of human DNA is identical with chimp DNA. </li></ul><ul><li>What accounts for the morphological and behavioral differences between the two ? </li></ul>
  47. 48. <ul><li>Skull bones : bones of face and brain chamber in humans increase in size at same rate from infant to adult while facial bones in chimps grow faster than the brain chamber  humans and chimps have different faces. </li></ul>
  48. 49. Proportional Changes in Skull chimpanzee human
  49. 50. Molecular Evidence <ul><li>Biochemical traits shared by species show how closely they are related </li></ul><ul><li>Can compare DNA, RNA, or proteins </li></ul>
  50. 51. Clues in DNA, RNA and Proteins <ul><li>All species have a mixture of ancestral and novel traits, including biochemical ones. </li></ul><ul><li>The kind and number of traits that species share are clues to evolutionary relationships. </li></ul><ul><li>Biochemical similarity is greatest among the most closely related species and smallest among the most remote. </li></ul>
  51. 52. Comparing Proteins <ul><li>Compare amino acid sequence of proteins produced by the same gene </li></ul><ul><li>Human cytochrome c (a protein) </li></ul><ul><ul><li>Identical amino acids in chimpanzee protein </li></ul></ul><ul><ul><li>Chicken protein differs by 18 amino acids </li></ul></ul><ul><ul><li>Yeast protein differs by 56 </li></ul></ul>
  52. 53. raccoon red panda giant panda spectacled bear sloth bear sun bear Asiatic black bear American black bear brown bear polar bear An example of how biochemical comparisons can assist in constructing and refining the evolutionary trees. Red pandas, giant pandas and brown bears was constructed using sequence Comparisons of mitochondrial and nuclear DNA. Findings indicated that red panda maybe more closely related to skunks, weasels and otter rather than to raccoons.
  53. 54. Sequence Conservation <ul><li>Cytochrome c functions in electron transport in cells. </li></ul><ul><li>Deficits in this vital protein would be lethal </li></ul><ul><li>Long sequences are identical in wheat, yeast, and a primate indicating the a.a. sequences has been highly conserved even in these three evolutionary distant lineages. </li></ul>
  54. 55. yeast wheat primate Yeast (top row) Wheat (middle) Primate (bottom) Amino acids are identical
  55. 56. Nucleic Acid Comparison <ul><li>Use single-stranded DNA or RNA </li></ul><ul><li>Hybrid molecules are created, then heated </li></ul><ul><li>The more heat required to break hybrid, the more closely related the species </li></ul>
  56. 57. Molecular Clock <ul><li>Assumption: “Ticks” (neutral mutations) accumulation in the DNA at a constant rate . </li></ul><ul><li>Count the number of differences in the DNA base sequences or a.a. sequences to estimate time of divergence among species or groups of them. </li></ul>
  57. 58. grown in water grown on land Differences in form between two plants of the same species Saggitaria sagittifolia . The leaf shapes are responses to different conditions in the environment, not the differences in the genes
  58. 59. Reproductive Isolation <ul><li>Cornerstone of the biological species concept </li></ul><ul><li>Speciation is the attainment of reproductive isolation </li></ul><ul><li>Reproductive isolation arises as a by-product of genetic change </li></ul>
  59. 60. Biological Species Concept <ul><li>“ Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.” </li></ul><ul><li>Ernst Mayr , evolutionary biologist </li></ul><ul><li>In other words, </li></ul><ul><li>Species as one or more groups of individuals that potentially can interbreed, produce fertile offspring and do not interbreed with other groups. </li></ul>
  60. 61. Reproductive Isolation <ul><li>In nature, sexually reproducing species attain and maintain separate identities by reproductive isolation ---the end of gene exchanges between populations. </li></ul><ul><li>New species arise by the evolutionary process of speciation. </li></ul><ul><li>This begins as gene flow ends between populations which diverge genetically as mutation, genetic drift and natural selection operate in each one independently. </li></ul>
  61. 62. Genetic Divergence <ul><li>Gradual accumulation of differences in the gene pools of populations </li></ul><ul><li>Natural selection, genetic drift, and mutation can contribute to divergence </li></ul><ul><li>Gene flow counters divergence </li></ul>
  62. 63. Genetic Divergence time A time B time C time D daughter species parent species
  63. 64. Reproductive isolating mechanisms <ul><li>Speciation occur after a very long period of divergence, or after one generation. </li></ul><ul><li>As two populations diverge, reproductive isolation mechanisms arise. </li></ul><ul><li>Such mechanisms are heritable aspects of body form, function or behavior that prevent interbreeding between different species and they reinforce differences between diverging populations. </li></ul>
  64. 65. Reproductive Isolating Mechanisms <ul><li>Prevent pollination or mating </li></ul><ul><li>Block fertilization or embryonic development </li></ul><ul><li>Cause offspring to be weak or sterile </li></ul>
  65. 66. Reproductive Isolation Mechanisms
  66. 67. Prezygotic Isolation Mechanism <ul><li>Mechanical isolation </li></ul><ul><li>Temporal isolation </li></ul><ul><li>Behavioral isolation </li></ul><ul><li>Ecological isolation </li></ul><ul><li>Gamete incompatibility /mortality </li></ul>
  67. 68. Mechanical Isolation <ul><li>Wasp and zebra orchid. </li></ul><ul><li>The plant release some chemicals that attract the insect which mistook the flower as the female. </li></ul>
  68. 69. <ul><li>Temporal isolation among cicadas </li></ul>Reproductive Isolation
  69. 70. Temporal Isolation <ul><li>Cicada </li></ul><ul><li>Timing of reproduction differs between 3 species. </li></ul><ul><li>If interbreeding occurs, it will take them to get together once every 221 years. </li></ul>
  70. 71. Behavioral Isolation <ul><li>Behavioral differences stop gene flow between related species. </li></ul><ul><li>Males and females engage in courtship displays before sex. </li></ul><ul><li>Female albatross recognizes the singing, wing spreading or head bobbing of a male of her species as an overture to sex. </li></ul><ul><li>Female of different species ignore this behavior. </li></ul>
  71. 72. Behavioral Isolation <ul><li>Albatrosses </li></ul>
  72. 73. Ecological Speciation <ul><li>Occurs to two populations in different microenvironments . </li></ul><ul><li>Manzanita species at foothills of Sierra Nevada: one at 600-1850m and the other at 750-3350m. They hybridize rarely. Both conserve water but one is adapted to less intense water stress while the other species lives in drier hillsides. </li></ul><ul><li>Thus, cross pollination is unlikely to happen. </li></ul>
  73. 74. Gamete Incompatibility <ul><li>If and whenever different species interbreed anyway, reproductive isolating mechanism does happen. </li></ul><ul><li>Reproductive cells of different species have molecular incompatibilities, so fertilization does not occur. </li></ul>
  74. 75. If whenever zygote form,but… <ul><li>Postzygotic isolating mechanisms take place. </li></ul><ul><li>Two consequences happen: </li></ul><ul><li>Hybrid inviability : Hybrid embryos die early or the new individuals die before they can reproduce </li></ul><ul><li>Hybrid sterility : Hybrid individuals cannot make functional gametes </li></ul><ul><li>Thus, no offspring, sterile offspring, weak offspring die before reproducing. </li></ul>
  75. 76. Postzygotic Isolating Mechanisms <ul><li>Early death </li></ul><ul><li>Sterility or sterile F2 offspring </li></ul><ul><li>Low survival rates </li></ul>
  76. 77. Llama-Camel Hybrid
  77. 78. Models for Speciation <ul><li>Allopatric speciation </li></ul><ul><li>Sympatric speciation </li></ul><ul><li>Parapatric speciation </li></ul>
  78. 79. Allopatric Speciation <ul><li>Speciation in geographically isolated populations </li></ul><ul><li>Some sort of barrier arises and prevents gene flow </li></ul><ul><li>Effectiveness of barrier varies with species </li></ul><ul><li>Gene flow ends, and genetic divergence give rise to daughter species. </li></ul>
  79. 80. Allopatric Speciation ilamas camels vicunas Connection of land bridge between two continents
  80. 81. Extensive Divergence Prevents Inbreeding <ul><li>Species separated by geographic barriers will diverge genetically </li></ul><ul><li>If divergence is great enough it will prevent inbreeding even if the barrier later disappears </li></ul>
  81. 82. Archipelagos <ul><li>Island chains some distance from continents </li></ul><ul><ul><li>Galapagos Islands </li></ul></ul><ul><ul><li>Hawaiian Islands </li></ul></ul><ul><li>Colonization of islands followed by genetic divergence sets the stage for speciation </li></ul>
  82. 83. 1 2 3 4 1 2 3 4 1 2 A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat. Later in time, a few individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence. Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island 1 by genetically different descendents of the ancestral species. 3 4
  83. 84. Hawaiian Islands <ul><li>Volcanic origins, variety of habitats </li></ul><ul><li>Adaptive radiations: </li></ul><ul><ul><li>Honeycreepers: in absence of other bird species, they radiated to fill numerous niches </li></ul></ul>Housefinch ( Carpodacus ) Ancestral type
  84. 85. Akepa ( Loxops coccineus ) Fig. 13-18d1, p.209 Speciation in Hawaiian Honeycreepers
  85. 86. Hawaiian honeycreepers <ul><li>An example of a burst of speciations on an isolated archipelago. </li></ul><ul><li>These species are adapted to diverse food sources, such as insects, seeds, fruits and floral nectar. </li></ul>
  86. 87. Speciation without a Barrier <ul><li>Sympatric speciation </li></ul><ul><ul><li>Species forms within the home range of the parent species </li></ul></ul><ul><li>Parapatric speciation </li></ul><ul><ul><li>Neighboring populations become distinct species while maintaining contact along a common border </li></ul></ul>
  87. 88. Sympatric Speciation <ul><ul><li>Daughter species arise from a population even in the absence of a physical barrier. </li></ul></ul><ul><ul><li>Polyploidy – speciation occur in an instant with a change in the chromosome number where </li></ul></ul><ul><ul><li>- duplication of somatic cells do not divide during mitosis or </li></ul></ul><ul><ul><li>- nondisjunction in meiosis resulting gametes with unreduced chromosome number </li></ul></ul>
  88. 89. Speciation by Polyploidy <ul><li>Change in chromosome number (3 n , 4 n , etc.) </li></ul><ul><li>Offspring with altered chromosome number cannot breed with parent population </li></ul><ul><li>Common mechanism of speciation in flowering plants </li></ul>
  89. 90. Possible Evolution of Wheat Figure 18.9 Page 299 Triticum monococcum (einkorn) T. aestivum (one of the common bread wheats) Unknown species of wild wheat T. turgidum (wild emmer) T. tauschii (a wild relative) 42AABBDD 14AA 14BB 14AB 28AABB 14DD X X cross-fertilization, followed by a spontaneous chromosome doubling
  90. 91. <ul><li>Sympatric speciation in wheat </li></ul>Possible Evolution of Wheat
  91. 92. Sympatric Speciation in African Cichlids <ul><li>Studied fish species in two lakes </li></ul><ul><li>Species in each lake are most likely descended from single ancestor </li></ul><ul><li>No barriers within either lake </li></ul>
  92. 93. Sympatric Speciation in African Cichlids <ul><li>Feeding preferences localize species in different parts of lake </li></ul>
  93. 94. Parapatric Speciation <ul><li>Occurs when one population extends across a broad region encompassing diverse habitats. </li></ul><ul><li>Different habitats exert distinct selection pressures on parts of population and maybe divergences leading towards speciation. </li></ul><ul><li>Hybrids form in between are less fit than individuals on either side of it. </li></ul><ul><li>Population maintaining contact along common border evolve into distinct species. </li></ul>
  94. 95. Parapatric Speciation <ul><li>Populations in contact along a common border </li></ul>giant velvet worm blind velvet worm
  95. 96. We’re All Related <ul><li>All species are related by descent </li></ul><ul><li>Share genetic connections that extend back in time to the prototypical cell </li></ul>
  96. 97. Gradual Model <ul><li>Species emerge through many small changes accumulating over time </li></ul><ul><li>Fits well with evidence from certain lineages in fossil record </li></ul><ul><li>Fossilized shells from vertical sequence of sedimentary rock layers. </li></ul><ul><li>First shell (bottom) – 64.5 mil yrs old </li></ul><ul><li>Most recent (top) – 68 mil yrs old </li></ul><ul><li>This analysis confirms the evolutionary order matches their geological sequence. </li></ul>
  97. 98. Punctuation Model <ul><li>Speciation model in which most changes in morphology are compressed into brief period near onset of divergence </li></ul><ul><li>Supported by fossil evidence in some lineages </li></ul>
  98. 99. Adaptive Radiation <ul><li>Burst of divergence </li></ul><ul><li>Single lineage gives rise to many new species </li></ul><ul><li>New species fill vacant adaptive zone </li></ul><ul><li>Adaptive zone is “way of life” </li></ul><ul><li>Cenozoic radiation of mammals </li></ul>
  99. 100. Adaptive Radiations of Mammals
  100. 101. Coevolution <ul><li>Process that close ecological interactions among species that cause them to evolve jointly. </li></ul><ul><li>Each species adapts to changes in the other; over time the two may become interdependent. </li></ul><ul><li>Some coevolved species no longer survive without one another. </li></ul><ul><li>Predator-prey ; host-parasite; flower-pollinator </li></ul>
  101. 102. Extinction <ul><li>Irrevocable loss of a species </li></ul><ul><li>Mass extinctions play a major role in evolutionary history </li></ul><ul><li>Fossil record shows 20 or more large-scale extinctions </li></ul><ul><li>Reduced diversity is followed by adaptive radiation </li></ul>
  102. 103. Who Survives? <ul><li>Species survival is somewhat random </li></ul><ul><li>Asteroids have repeatedly struck Earth, destroying many lineages </li></ul><ul><li>Changes in global temperature favor lineages that are widely distributed </li></ul>
  103. 104. Evolutionary Theory <ul><li>Involves processes of both macroevolution and microevolution. </li></ul><ul><li>All come to explain the same thing--- the tree of life that connects all species by ancestry. </li></ul>
  104. 105. Microevolution <ul><li>Involves processes: </li></ul><ul><li>Natural selection  preserves or erodes species cohesion depending on environmental pressures </li></ul><ul><li>Mutation  original source of alleles </li></ul><ul><li>Gene flow  preserves species of cohesion </li></ul><ul><li>Gene drift  erodes species of cohesion </li></ul><ul><li>Stability or change in a species is the outcome of balances / imbalances among all of the above processes. The effects are influenced by population size and the prevailing environmental conditions. </li></ul>
  105. 106. Macroevolution <ul><li>Describe genetic changes within a species or population. </li></ul><ul><li>Is our name for large-scale pattern such as one species giving rise to several others, the origin of major groups, and major extinction events. </li></ul><ul><li>Involves: </li></ul><ul><li>Genetic persistence  basis of unity of life (biochemical and molecular basis of inheritance) </li></ul><ul><li>Genetic divergence  basis of life’s diversity (adaptive radiation, branching with rates and times of change) </li></ul><ul><li>Genetic disconnect  extinction (end of line of the species brought by catastrophic events) </li></ul>
  106. 107. Organizing information about species <ul><li>Connections among species, from ancient to recent, are evidence of evolution. </li></ul><ul><li>Species are put into groups based on what we know about their evolutionary relationships. </li></ul><ul><li>Taxonomy is a set of rules of naming organisms and classifying them into series of ranks based on their traits. </li></ul><ul><li>e.g. every organism has a unique two-part scientific name. Genus-species. ( Homo sapien ) </li></ul>
  107. 108. Taxonomy <ul><li>The identification, naming, and classification of species </li></ul><ul><li>Somewhat subjective </li></ul><ul><li>Information about species can be interpreted differently </li></ul>
  108. 109. The higher taxa <ul><li>A taxon (plural, taxa) is an organism or group of them.Categories above species are higher taxa.Each higher taxon consists of a group of the next lower taxon. </li></ul><ul><li>Lead to the classification system developed by a Swedish naturalist, Carolus Linnaeus (1707-1778), who separated animals and plants according to certain physical similarities and gave identifying names to each species. </li></ul><ul><li>Linnaeus’s system classified plants and animals on seven levels, using Latin and Greek words. </li></ul>
  109. 110. Principles and importance of taxonomy <ul><li>Taxonomy as of science of classification </li></ul><ul><li>Important to find, identify, study, describe and understand the distribution of organisms </li></ul><ul><li>grouping/classify organisms according to their shared common features (as of taxon ) </li></ul><ul><li>based on seven levels of taxon: </li></ul>
  110. 111. Taxa (plural) Taxon (singular) <ul><li>Kingdom </li></ul><ul><li>Phylum </li></ul><ul><li>Class </li></ul><ul><li>Order </li></ul><ul><li>Family </li></ul><ul><li>Genus </li></ul><ul><li>Species </li></ul>
  111. 112. Levels of taxon Kingdom largest group sharing common features Phylum Subdividision of kingdom; contain large number of organism that have one / two fundamental features Class Group of orders within a phylum Order Group of related families Family Group of related genera Genus Group of similar and closely-related species Species Group of individuals which share a large number of features and capable of inbreeding to produce fertile offspring
  112. 113. Take note!! <ul><li>Number of organisms in each taxon decreases as we goes down the levels of taxon. </li></ul><ul><li>Number of shared characteristics increases as we go up the levels of taxon. </li></ul>Kingdom Phylum Class Order Family Genus Species
  113. 114. Classification of a single species of animal
  114. 115. How a brown squirrel is classified: <ul><li>Kingdom (Animalia, or “animal”) </li></ul><ul><li>Phylum (Chordata, or “has a backbone”) </li></ul><ul><li>Class (Mammalia, or “has a backbone and nurses its young”) </li></ul><ul><li>Order (Rodentia, or “has a backbone, nurses its young, and has long, sharp front teeth) </li></ul><ul><li>Family (Scuridae, or “has a backbone, nurses its young, has long, sharp front teeth, and has a bushy tail) </li></ul><ul><li>Genus ( Tamiasciurus , or “has a backbone, nurses its young, has long, sharp front teeth, has a bushy tail, and climbs trees) </li></ul><ul><li>Species ( hudsonicus , or “has a backbone, nurses its young, has long, sharp front teeth, has a bushy tail, climbs trees and has brown fur on its back and white fur on its underparts) </li></ul><ul><li>It is not necessary to go through the entire seven-level classification system to identify a plant or animal. </li></ul><ul><li>Two names are sufficient—the genus and species names. </li></ul><ul><li>Thus, the scientific name for the brown squirrel is Tamiasciurus hudsonicus . </li></ul>
  115. 116. <ul><li>Because two names are used, the system used by Linnaeus and based on Latin is known as the binomial (two names) system of nomenclature (naming). </li></ul><ul><li>The naming of species and other taxa follows a set of rules: </li></ul><ul><li>International Code of Botanical Nomenclature (ICBN) for plants, </li></ul><ul><li>International Code of Zoological Nomenclature (ICZN) for animals. </li></ul>The name game
  116. 117. Naming Species <ul><li>Each species has a two-part name </li></ul><ul><li>First part is generic name </li></ul><ul><li>Second part is species name </li></ul><ul><li>Ursus arctos = brown bear </li></ul><ul><li>Ursus americanus = black bear </li></ul><ul><li>Bufo americanus = American toad </li></ul>
  117. 118. Rules of the game <ul><li>Consistency in using the system of classification. </li></ul><ul><li>The generic (genus) name is the first and always given with capital letter </li></ul><ul><li>The specific (species) name comes second and always starts with small letter. </li></ul><ul><li>Both names should either be written in Italics or underlined </li></ul><ul><li>Scientific name should be written in full the first time it is used. But after that, it can be abbreviated. </li></ul><ul><li>If the species is unknown, then the abbreviation `sp.’ can be used. </li></ul>
  118. 119. Some general rules for nomenclature: <ul><li>All taxa must belong to a higher taxonomic group. Often a newly discovered organism is the sole species in a single genus, within a single family...etc. </li></ul><ul><li>The first name to be validly and effectively published has priority. This rule has caused numerous name changes, especially with fossil organisms: Brontosaurus is invalid, and the correct name for the big sauropod dinosaur is Apatosaurus , Eohippus (the tiny &quot;dawn horse&quot;) is invalid and should be referred to as Hyracotherium . Sometime, however, names can be conserved if a group of systematists agrees. </li></ul><ul><li>All taxa must have an author. When you see a scientific name such as Homo sapiens L, the L stands for Linnaeus, who first described and named that organism. Most scientists must have their names spelled out. </li></ul>
  119. 120. Taxonomy of a selected plant species. Note that the Kingdoms have a great deal more types of creatures in them than do species.
  120. 121. <ul><li>The system is successful because : </li></ul><ul><ul><li>each particular organism has its own unique scientific name </li></ul></ul><ul><ul><li>can see that two species are closely related based on similar/same genus. </li></ul></ul>
  121. 122. Examples of Classification Plantae Juniperus J. occidentalis Cupressaceae Cuoniferales Coniferopsida Coniferophyta Plantae Vanilla V. planifolia Orchidaceae Asparagales Monocotyledonae Anthophyta western juniper vanilla orchid housefly human Kingdom Genus Species Family Order Class Phylum Animalia Musca M. domestica Muscidae Diptera Insecta Anthropoda Animalia Homo H. sapiens Hominidae Primates Mammalia Chordata
  122. 123. Taxonomic Classification
  123. 124. Taxonomic Classification
  124. 125. Phylogeny <ul><li>The scientific study of evolutionary relationships among species </li></ul><ul><li>Practical applications </li></ul><ul><ul><li>Allows predictions about the needs or weaknesses of one species on the basis of its known relationship to another </li></ul></ul>
  125. 126. Six-Kingdom Classification Bacteria Archaea Protists Plants Fungi Animals
  126. 127. Three-Domain System Bacteria Archaea Eukarya
  127. 128. Tree of Life
  128. 129. Classification systems <ul><li>Evolutionary tree for plants </li></ul>
  129. 130. Cladistics <ul><li>Cladistics is a set of methods by which we can determine the evolutionary relationships and used in phylogenetics classification schemes. </li></ul><ul><li>Organisms are grouped by shared derived traits. </li></ul><ul><li>Monophyletic group - A group of species all descended from an ancestral species in which a particular derived trait first evolved. </li></ul>
  130. 131. Patterns of Change in a Lineage <ul><li>Cladogenesis </li></ul><ul><ul><li>Branching pattern </li></ul></ul><ul><ul><li>Lineage splits, isolated populations diverge </li></ul></ul><ul><li>Anagenesis </li></ul><ul><ul><li>No branching </li></ul></ul><ul><ul><li>Changes occur within single lineage </li></ul></ul><ul><ul><li>Gene flow throughout process among its population </li></ul></ul><ul><ul><li>In time, species becomes so different from its ancestor  becomes a new species and the ancestral species  extinct. </li></ul></ul>
  131. 132. Evolutionary Trees ancestral stock species 1 species 2 species 3 Summarize information about relationships among groups branch point (time of genetic divergence, speciation under way) suspected branching
  132. 133. <ul><li>Evolutionary tree diagram </li></ul>Evolutionary Trees
  133. 134. Cladistic approach <ul><li>A clade is a group of species that share a set of derived traits (those that do not appear in the most recent ancestor). </li></ul><ul><li>A clade may correspond to the Linnaean group but not every Linnaean group correspond to a clade. </li></ul><ul><li>With biochemistry approach and DNA sequencing methods, data used to define a clade can be updated frequently . </li></ul>
  134. 135. A Cladogram
  135. 136. Evolutionary Tree <ul><li>Summarize our best understanding of the pattern of evolution for a group of organisms. </li></ul>
  136. 137. Evolutionary Tree
  137. 138. Current Evolutionary Tree
  138. 139. How to construct a Cladogram <ul><li>Using a selection of traits among groups to construct a simple cladogram, step by step approach. </li></ul><ul><li>Is an estimate of ‘who came from whom’ </li></ul><ul><li>Has no time bar with absolute dates. </li></ul><ul><li>Reflect morphological and biochemical comparisons </li></ul><ul><li>Help to visualize monophyletic groups as sets within sets. </li></ul><ul><li>Reference: </li></ul><ul><li> </li></ul>
  139. 140. Step 1 <ul><li>Start with a list of taxa that are to be fit into the cladogram (the ingroup) and their derived characters.  </li></ul><ul><li>Choose an outgroup; a taxa that shares a primitive character with the ingroup, but exhibits none of the derived characters.  </li></ul>
  140. 142. Step 2 <ul><li>Fill in a character table that will be used to make the cladogram.  The taxon with the least number of derived characters should be the first row.  The taxon with the greatest number of derived characters should be the last row.  </li></ul><ul><li>The character that is seen in the greatest number of taxa should be the first column.  The character that is exhibited in the least number of taxa should be the last column.  </li></ul><ul><li>Use ones and zeroes to represent presence (1) or absence (0) of specific characters in specific species. </li></ul>
  141. 144. Make a Venn diagram to place the 8 animals in groups to illustrate those characteristics which different animals have in common. chimp human chimpanzee Amphioxus : no back bone Lamprey : has backbone Sunfish : has jaws Lizard : has amniotic egg Bear: has mammary glands Newt : has four limbs
  142. 145. Step 3 <ul><li>Build the cladogram step-by-step.  Start with the first character (first column).  </li></ul><ul><li>The outgroup is the only taxon that doesn't exhibit the first character.  </li></ul><ul><li>Separate it from the other taxa on the cladogram.  </li></ul><ul><li>Remember that the outgroup shares a common ancestor with the ingroup.  </li></ul><ul><li>Each split in the cladogram marks a separate evolutionary event.    </li></ul>
  143. 149. Step 4 <ul><li>By looking at the completed cladogram, we can see which species are most closely or distantly related.  </li></ul><ul><li>In this example, humans are more closely related to chimpanzees, than to any other taxon on the cladogram.  </li></ul>
  144. 151. <ul><li>Do the Bring Home Quiz provided in the next slide. You are to complete the assignment as during the next lecture, answers shall be given and marking shall be carried out at the same time. </li></ul><ul><li>Marked assignment must be hand over back to the instructor as marks shall be counted as part of the assessment. </li></ul><ul><li>Those did not bring in their assignment for the next lecture are considered FAIL (zero % is given). </li></ul>
  145. 152. BRING HOME QUIZ (20 marks) <ul><li>Follow the instruction provided in the text below. </li></ul><ul><li>For the following animals, construct your own cladogram (+ means that the animal has the given derived character trait) showing : </li></ul><ul><li>character table (3 marks) ; </li></ul><ul><li>Venn diagram (7 marks) and </li></ul><ul><li>completed cladogram (8 marks) .  </li></ul><ul><li>*Make sure that you apply the steps as outlined from the lecture. </li></ul>
  146. 153. BRING HOME QUIZ Derived Characters segmented jaws hair placenta multicellular limbs kangaroo + + + - + + earthworm + - - - + - amoeba - - - - - - lizard + + - - + + cat + + + + + + sponge - - - - + - salmon + + - - + -
  147. 154. <ul><li>Based on the completed cladogram that you have constructed, answer the following questions: </li></ul><ul><li>Which ingroup is most closely related to sponges?(1 mark) </li></ul><ul><li>________________________________ </li></ul><ul><li>Which ingroup is most distantly related to sponges?(1 mark) </li></ul><ul><li>________________________________ </li></ul><ul><li>TOTAL : 20 marks </li></ul>