6a macroevolution


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6a macroevolution

  1. 1. Lecture 6a: Macroevolution Macroevolution
  2. 2. Macroevolution <ul><li>Not really different than microevolution, but over a much larger scale </li></ul><ul><li>Changes to species, not changes to populations </li></ul>
  3. 3. Species- what are they anyway? <ul><li>Biolgical Species Concept : members of the same species interbreed and have a shared gene pool, but are reproductively isolated from every other species </li></ul><ul><li>Speciation : the evolution of new species </li></ul>
  4. 4. Species <ul><li>Two animals of the same species can reproduce and have fertile offspring </li></ul><ul><li>One species can consist of one or many populations </li></ul><ul><li>Appearance does not necessarily allow you to tell two species apart </li></ul>
  5. 5. Reproductive Barriers <ul><li>As speciation occurs, reproductive barriers arise that prevent breeding from occurring between the different species </li></ul><ul><li>Barriers fall into two categories: prezygotic and postzygotic </li></ul>
  6. 6. Prezygotic Barriers <ul><li>Habitat Isolation: The different species inhabit different habitats </li></ul><ul><li>Temporal Isolation: Breeding season is at different times of the year </li></ul><ul><li>Behavioral Isolation: Pheromones, courtship rituals, songs or calls, etc are different </li></ul><ul><li>Mechanical Isolation: Genitalia are incompatible </li></ul><ul><li>Gamete Isolation: The gametes can not fuse to form a zygote </li></ul>
  7. 7. Postzygotic Barriers <ul><li>Zygote mortality: A zygote is formed, but it does not survive </li></ul><ul><li>Hybrid sterility: The zygote develops into an adult, but it is sterile </li></ul><ul><li>F2 Fitness: The hybrids can reproduce, but the F2 generation can not </li></ul>
  8. 8. Types of Speciation <ul><li>Allopatric Speciation </li></ul><ul><ul><li>Occurs when populations become geographically isolated, and move further and further apart genetically from the original species </li></ul></ul><ul><ul><li>Ex. Ensatina salamanders, iguanas </li></ul></ul>
  9. 9. Types of Speciation <ul><li>Sympatric speciation </li></ul><ul><ul><li>Population develops into two or more groups without geographic isolation </li></ul></ul><ul><ul><li>Polyploidy: increase in number of chromosomes to 3n or higher due to hybridization, sometimes followed by doubling of chromosomes- results in 3rd species </li></ul></ul>
  10. 10. Types of Speciation <ul><li>Adaptive Radiation </li></ul><ul><ul><li>New species evolve from one ancestral species to fill different niches in the habitat </li></ul></ul><ul><ul><li>Ex. Galapagos finches, Hawaiian honeycreepers </li></ul></ul>
  11. 11. Fossils <ul><li>To study extinct species, especially ones from millions of years ago, we look to fossils: </li></ul><ul><ul><li>The remains or traces of past life </li></ul></ul><ul><ul><li>Can take several forms- amber, footprints, petrification, actual remains </li></ul></ul>
  12. 12. Geologic Time <ul><li>See timeline </li></ul><ul><li>Cambrian explosion: all major groups of animals appeared </li></ul><ul><li>Number of species on Earth has continued to increase over time, even to the present day </li></ul>
  13. 14. Speciation <ul><li>We do not know how quickly species arise- there are two models: </li></ul><ul><ul><li>Gradualistic Model- slow steady change over a long period of time </li></ul></ul><ul><ul><li>Punctuated Equilibrium: somewhat ‘sudden’ appearance of new species in fossil record </li></ul></ul><ul><ul><ul><li>The transitional fossils are unlikely due to geographic isolation and small numbers </li></ul></ul></ul>
  14. 15. Mass Extinctions <ul><li>Relatively sudden disappearances of large numbers of species </li></ul><ul><li>Have been several, of course dinos the best known example </li></ul><ul><li>Two main causes: Continental drift and meteorite impacts </li></ul>
  15. 16. Continental Drift <ul><li>The continents on Earth are moving </li></ul><ul><li>Plate tectonics: The crust of Earth is floating on the molten mantle, the crust is in several pieces </li></ul><ul><li>As the continents move, the climate changes </li></ul>
  16. 17. Pangaea: its formation 250 mya was probably the cause of the Permian Extinction
  17. 18. Meteorites <ul><li>Probably the cause of the dinosaur’s extinction </li></ul><ul><ul><li>Caused massive cloud of dust that blocked the sun, lowering temperatures worldwide </li></ul></ul><ul><ul><li>Soot and iridium are found in Cretaceous clay, and a crater has been identified as well </li></ul></ul>
  18. 19. Systematics <ul><li>DKPCOFGS </li></ul><ul><li>As the category gets higher and higher, it gets more and more inclusive </li></ul><ul><li>Ideally, organisms are classified according to their evolutionary relationships, so taxonomy is in constant flux as we learn more and more </li></ul>
  19. 20. Phylogenetic Trees <ul><li>Trees that show relatedness of different organisms </li></ul><ul><ul><li>Indicate common ancestor, and lines of descent </li></ul></ul><ul><ul><li>Determined using comparative anatomy, embryology, molecular evidence </li></ul></ul>
  20. 21. Anatomy <ul><li>Remember, it matters where the characteristic in question arose from, not what it does now </li></ul><ul><ul><li>Ex. Thorny devils vs. horny toads have Analagous structures </li></ul></ul><ul><ul><li>Ex. Vertebrate forelimbs are Homologous structures </li></ul></ul>
  21. 22. Using DNA to determine relationships <ul><li>Remember: evolution occurs when mutations in DNA occur-- it can not occur without those random changes </li></ul><ul><ul><li>Therefore, the more closely related animals are, the fewer differences there will be in their DNA </li></ul></ul><ul><ul><li>This allows new information about DNA to be included in our understanding of how life on Earth evolved </li></ul></ul>