Origen of Species

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Siobhan
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146750
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Origen of Species
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2012-04-10 10:45:13
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Origen Species
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Origen of Species
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  1. The Biological Species Concept
    • species: a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations
    • Limitations:
    • cannot be applied to fossils or asexual organisms
    • Difficult to directly observe interbreeding for all organisms
    • emphasizes absence of gene flow- looking at limited population
    • But…gene flow can occur between distinct species



  2. Reproductive Isolation
    • existence of biological factors (barriers)

    • Premating Isolating Mechanisms: ideas?
    • Prevents mating between species
    • Ex- Mating Calls. If one species uses external
    • fertilization and another uses internal, they cannot
    • Postmating Mechanisms
    • Prevents formation of fertile offspring
    • Ex- chromosomal differences- cannot undergo
    • meiosis- infertile
  3. Premating Isolating Mechanisms:
    • Prevents mating between species
    • Ex- Mating Calls. If one species uses external
    • fertilization and another uses internal, they cannot

  4. Postmating Mechanisms
    • Prevents formation of fertile offspring
    • Ex- chromosomal differences- cannot undergo
    • meiosis- infertile
  5. Prezygotic barriers mechanisms b
    • Prezygotic barriers mechanisms block fertilization
    • geographic: can allow new species to form
    • ecological: eat different food, different habitat
    • temporal: different mating seasons
    • Gametic Isolation: Sperm of one species may not be able to fertilize eggs of another species


  6. geographic barrier
    can allow new species to form
  7. ecological BARRIER
    eat different food, different habitat
  8. temporal barrier
    • different mating seasons
  9. Gametic Isolation
    • Sperm of one species may not be able to fertilize eggs of another species

  10. Behavioral isolation:
    • Courtship rituals
  11. Mechanical isolation:
    Morphological differences can prevent successful mating
  12. Postzygotic barriers
    • Postzygotic barriers: prevent the hybrid zygote from developing into a viable, fertile adult
    • Reduced hybrid viability (failure to learn: hunt, nest)
    • Reduced hybrid fertility (mule, liger)
    • Gametic incompatibility

  13. Other species concepts emphasize the unity
    • morphological species concept : defines by structural features
    • ecological species concept : in terms of its ecological niche
    • phylogenetic species concept: the smallest group of individuals on a phylogenetic tree (share a common ancestor)
  14. morphological species concept
    • defines by structural features
  15. ecological species concept
    • : in terms of its ecological niche
  16. phylogenetic species concep
    • the smallest group of individuals on a phylogenetic tree (share a common ancestor)

  17. How Do New Species Form?
    • 1) Isolation of populations-block interbreeding
    • Allopatric speciation: other homeland

    • 2) Genetic divergence of populations
    • Sympatric speciation: together
  18. Allopatric speciation
    • Isolation of populations-block interbreeding
    • Allopatric speciation: other homeland
    • gene flow is interrupted or reduced
    • Accumulate genetic differences
    • Genetic drift-founder effect
    • Most common source of new species
    • The definition of barrier depends on the ability of a population to disperse
    • For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen


    • For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland
  19. Sympatric speciation:
    • Genetic divergence of populations
    • Sympatric speciation: together
    • Speciation takes place in geographically overlapping populations

    the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees


  20. Polyploidy
    • Polyploidy : extra sets of chromosomes due to accidents during cell division
    • Crops: oats, cotton, potatoes, tobacco, and wheat
    • more common in plants than in animals
    • Mutations can lead to polyploidy and often result in sympatric speciation


  21. Sexual Selection
    • Sexual selection can drive sympatric speciation



  22. Allopatric and Sympatric Speciation:
    A Review
    • In allopatric speciation, geographic isolation restricts gene flow between populations
    • Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
    • Even if contact is restored between populations, interbreeding is prevented
    • In sympatric speciation, a reproductive barrier (snails) isolates a subset of a population without geographic separation from the parent species
    • Sympatric speciation can result from polyploidy, natural selection, or sexual selection

  23. Hybrid zones reveal
    • Hybrid zones reveal factors that cause reproductive isolation
    • A hybrid zone is a region in which members of different species mate and produce hybrids
    • Hybrids are the result of mating between species with incomplete reproductive barriers
    • Hybrids often have reduced fitness compared with parent species- have to adapt
    • The distribution of hybrid zones can be more complex if parent species are found in patches within the same region

  24. Macroevolution
    • Macroevolution is the cumulative effect of many speciation and extinction events
  25. Extinction
    • Extinction is the death of all members of a species
    • At least 99.9% of all species that ever existed are now extinct
    • The immediate cause of extinction is usually environmental change
    • habitat destruction
    • Frogs because rain forest destruction
    • increased competition among species
    • Where food is scarce- dessert,
    • Overspecialization
    • Pandas- overspecialized in bamboo

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