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    Macroevolution Macroevolution Presentation Transcript

    • Lecture 6a: Macroevolution Macroevolution
    • Macroevolution
      • Not really different than microevolution, but over a much larger scale
      • Changes to species, not changes to populations
    • 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
    • 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
    • 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
    • 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
    • Behavioral isolation: Different dewlaps in Anolis lizards
    • Mechanical isolation: Watersnake hemipenes
    • 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
    • Hybrid Sterility: Both mules and zonkeys are sterile
    • 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
    • Allopatric speciation in Galapagos finches
    • 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
    • Types of Speciation
      • Adaptive Radiation
        • New species evolve from one ancestral species to fill different niches in the habitat
        • Ex. Galapagos finches, Hawaiian honeycreepers
    • Adaptive radiation in cichlid fish, species have evolved to eat different food sources and to feed in different ways
    • 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
    • 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
    • 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
    • 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
    • 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
    • Pangaea: its formation 250 mya was probably the cause of the Permian Extinction
    • 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
    • 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
    • Phylogenetic Trees
      • Trees that show relatedness of different organisms
        • Indicate common ancestor, and lines of descent
        • Determined using comparative anatomy, embryology, molecular evidence
    • Phylogenetic Tree of chordates
    • Phylogenetic tree of canines
    • 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
    • Thorny devil (Australia) Horned lizard (US) Analogous structures- horns on two lizards
    • Homologous structures- front limbs of several vertebrates
    • 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