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6a macroevolution

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Transcript

  • 1. Lecture 6a: Macroevolution Macroevolution
  • 2. Macroevolution
    • Not really different than microevolution, but over a much larger scale
    • Changes to species, not changes to populations
  • 3. Species- what are they anyway?
    • Biolgical Species Concept : members of the same species interbreed and have a shared gene pool, but are reproductively isolated from every other species
    • Speciation : the evolution of new species
  • 4. Species
    • Two animals of the same species can reproduce and have fertile offspring
    • One species can consist of one or many populations
    • Appearance does not necessarily allow you to tell two species apart
  • 5. Reproductive Barriers
    • As speciation occurs, reproductive barriers arise that prevent breeding from occurring between the different species
    • Barriers fall into two categories: prezygotic and postzygotic
  • 6. Prezygotic Barriers
    • Habitat Isolation: The different species inhabit different habitats
    • Temporal Isolation: Breeding season is at different times of the year
    • Behavioral Isolation: Pheromones, courtship rituals, songs or calls, etc are different
    • Mechanical Isolation: Genitalia are incompatible
    • Gamete Isolation: The gametes can not fuse to form a zygote
  • 7. Postzygotic Barriers
    • Zygote mortality: A zygote is formed, but it does not survive
    • Hybrid sterility: The zygote develops into an adult, but it is sterile
    • F2 Fitness: The hybrids can reproduce, but the F2 generation can not
  • 8. Types of Speciation
    • Allopatric Speciation
      • Occurs when populations become geographically isolated, and move further and further apart genetically from the original species
      • Ex. Ensatina salamanders, iguanas
  • 9. Types of Speciation
    • Sympatric speciation
      • Population develops into two or more groups without geographic isolation
      • Polyploidy: increase in number of chromosomes to 3n or higher due to hybridization, sometimes followed by doubling of chromosomes- results in 3rd species
  • 10. Types of Speciation
    • Adaptive Radiation
      • New species evolve from one ancestral species to fill different niches in the habitat
      • Ex. Galapagos finches, Hawaiian honeycreepers
  • 11. Fossils
    • To study extinct species, especially ones from millions of years ago, we look to fossils:
      • The remains or traces of past life
      • Can take several forms- amber, footprints, petrification, actual remains
  • 12. Geologic Time
    • See timeline
    • Cambrian explosion: all major groups of animals appeared
    • Number of species on Earth has continued to increase over time, even to the present day
  • 13.  
  • 14. Speciation
    • We do not know how quickly species arise- there are two models:
      • Gradualistic Model- slow steady change over a long period of time
      • Punctuated Equilibrium: somewhat ‘sudden’ appearance of new species in fossil record
        • The transitional fossils are unlikely due to geographic isolation and small numbers
  • 15. Mass Extinctions
    • Relatively sudden disappearances of large numbers of species
    • Have been several, of course dinos the best known example
    • Two main causes: Continental drift and meteorite impacts
  • 16. Continental Drift
    • The continents on Earth are moving
    • Plate tectonics: The crust of Earth is floating on the molten mantle, the crust is in several pieces
    • As the continents move, the climate changes
  • 17. Pangaea: its formation 250 mya was probably the cause of the Permian Extinction
  • 18. Meteorites
    • Probably the cause of the dinosaur’s extinction
      • Caused massive cloud of dust that blocked the sun, lowering temperatures worldwide
      • Soot and iridium are found in Cretaceous clay, and a crater has been identified as well
  • 19. Systematics
    • DKPCOFGS
    • As the category gets higher and higher, it gets more and more inclusive
    • Ideally, organisms are classified according to their evolutionary relationships, so taxonomy is in constant flux as we learn more and more
  • 20. Phylogenetic Trees
    • Trees that show relatedness of different organisms
      • Indicate common ancestor, and lines of descent
      • Determined using comparative anatomy, embryology, molecular evidence
  • 21. Anatomy
    • Remember, it matters where the characteristic in question arose from, not what it does now
      • Ex. Thorny devils vs. horny toads have Analagous structures
      • Ex. Vertebrate forelimbs are Homologous structures
  • 22. Using DNA to determine relationships
    • Remember: evolution occurs when mutations in DNA occur-- it can not occur without those random changes
      • Therefore, the more closely related animals are, the fewer differences there will be in their DNA
      • This allows new information about DNA to be included in our understanding of how life on Earth evolved
  • 23.