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The Formation of Species

The Formation of Species. How do new species of organisms arise?. What does “different species” mean?. Species: group of populations whose members have the potential to interbreed and produce fertile offspring. What kind of barriers can separate species?.

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The Formation of Species

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  1. The Formation of Species How do new species of organisms arise?

  2. What does “different species” mean? • Species: group of populations whose members have the potential to interbreed and produce fertile offspring

  3. What kind of barriers can separate species? • Prezygotic: Before fertilization ever takes place (more common mechanism). • 5 types of Prezygotic barriers • Postzygotic: After fertilization take place (after the zygote is formed). • 3 types of Postzygotic barriers

  4. Prezygotic 1: Temporal Isolation • Mating/flowering occurs in different seasons or at different times of day.

  5. Prezygotic 2: Habitat Isolation • 2 species live in the same general area but not the same kinds of places

  6. Prezygotic 3: Behavioral Isolation • Males and females respond to signals only from members of their own species

  7. Prezygotic 4: Mechanical Isolation • Male and female sex organs are not compatible

  8. Prezygotic 5: Gamete Isolation • Egg and sperm from a particular species only recognize each other.

  9. Postzygotic 1: Reduced hybrid viability • 2 different species can produce offspring, but they do not survive to reproduce

  10. Postzygotic 2: Reduced hybrid fertility • 2 species can produce offspring, but the offspring are not fertile

  11. Postzygotic 3: Hybrid breakdown • 2 different species may produce offspring. These offspring may be fertile, but further generations are weak or infertile

  12. Mechanisms of Speciation • Allopatric Speciation: “allos” = other; “patra” = fatherland; physical separation of members of the same species can lead to different species over time

  13. Mechanisms of Speciation • Sympatric Speciation: “syn” = together; “patra” = fatherland; physical separation is not required for different species to form • 1. Habitat differentiation • 2. Sexual selection • 3. Polyploidy

  14. Polyploidy: Instantaneous Speciation

  15. Polyploidy: Instantaneous Speciation

  16. The Story of Bread Wheat

  17. The Story of Bread Wheat

  18. As a Population Changes, Reproductive Barriers May Develop • Back to fruit flies…

  19. Hybrids: When Speciation is Not Quite Complete

  20. The Fate of Hybrids

  21. Speciation can be Fast or Slow • Punctuated Equilibrium Model

  22. Speciation can be Fast or Slow • Gradualism Model

  23. Just How Long Does Speciation Take? • Range: 4,000 years to 40 million years, but rarely less than 500,000 years. • Average: 6.5 million years

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