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Types of evolutionary change

Anagenesis Microevolution adaptive change within species “descent with modification”. Cladogenesis Macroevolution derivation of new species from previously existing ones “transmutation of species”. Types of evolutionary change. Macroevolution. What is a species?

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Types of evolutionary change

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  1. Anagenesis Microevolution adaptive change within species “descent with modification” Cladogenesis Macroevolution derivation of new species from previously existing ones “transmutation of species” Types of evolutionary change

  2. Macroevolution • What is a species? • How do species originate? • Speciation is the evolution of reproductive isolation between once-interbreeding populations • How is reproductive isolation achieved?

  3. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms…

  4. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Geographic isolation (species occupy different geographic ranges; they are “allopatric”)

  5. Reproductive isolating mechanismsgeographic isolation

  6. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Habitat isolation (species are “sympatric” but occupy different habitats)

  7. Reproductive isolating mechanisms • Habitat isolation (species are “sympatric” but occupy different habitats)

  8. Reproductive isolating mechanisms Peromyscus maniculatus, the deer mouse; prefers woods rather than fields Peromyscus leucopus, the white-footed mouse; prefers fields rather than woods

  9. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Temporal isolation (species are sympatric and occupy similar habitats, but breed at different times of the year)

  10. Reproductive isolating mechanisms Sciurus carolinensis, the gray squirrel, breeds in July and August Sciurus niger, the fox squirrel, breeds in May and June

  11. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Behavioral isolation (species are sympatric and occupy similar habitats, and breed at the same time of the year, but have different courtship behaviors)

  12. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms - Behavioral isolation Bluestripe butterflyfish Ornate butterflyfish

  13. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Mechanical isolation (species are sympatric and occupy similar habitats, and breed at the same time of the year, and have similar courtship behaviors, but the penis won’t fit into the vagina)

  14. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Mechanical isolation is common in insects • the morphology of the female reproductive tract is complex, and the male’s copulatory organ must fit precisely for insemination to occur

  15. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • mating (copulation) does not necessarily lead to insemination

  16. Reproductive isolating mechanisms:mechanical isolation spermatheca copulatory bursa spermathecal duct oviduct vagina

  17. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Gamete mortality (sperm and eggs are incompatible; gametes die before forming a zygote) • In some cases, the female metabolizes the sperm and uses the material to produce eggs

  18. Reproductive isolating mechanisms • Prezygotic reproductive isolating mechanisms • Gamete mortality (sperm and eggs are incompatible; gametes die before forming a zygote) • In some cases, the female metabolizes the sperm and uses the material to produce eggs • insemination does not necessarily lead to fertilization

  19. Reproductive isolating mechanisms • What happens if the sperm fertilize the egg? sperm and egg cartoon here

  20. Reproductive isolating mechanisms • What happens if the sperm fertilize the egg? • Formation of a “hybrid” zygote

  21. Reproductive isolating mechanisms • What happens if the sperm fertilize the egg? • Formation of a “hybrid” zygote • Does this mean that reproductive isolation is not achieved?

  22. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms…

  23. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid inviability; death of the hybrid may occur anytime during development from conception onward; if the hybrid is inviable it cannot reproduce

  24. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid sterility; the hybrid may survive but be unable to produce fertile gametes • For instance, horses and donkeys hybridize to produce mules, which are sterile

  25. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid reproductive disadvantage; the hybrid may survive and produce fertile gametes, and may “back-cross” with one of the parental species, but the resulting offspring will be at a survival or reproductive disadvantage

  26. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid reproductive disadvantage • How will natural selection act in this situation?

  27. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid reproductive disadvantage • How will natural selection act in this situation? • Selection promotes the evolution of reproductive isolation by acting in favor of individuals that do not hybridize (against those that do)

  28. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid reproductive disadvantage • How will natural selection act in this situation? • Selection promotes the evolution of reproductive isolation by acting in favor of individuals that do not hybridize (against those that do) • This process is called “reinforcement”

  29. Reproductive isolating mechanisms • Postzygotic reproductive isolating mechanisms • Hybrid reproductive disadvantage • How will natural selection act in this situation? • Selection promotes the evolution of reproductive isolation by acting in favor of individuals that do not hybridize (against those that do) • This process is called “reinforcement” • Reinforcement leads to the evolution of prezygotic mechanisms…

  30. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage…

  31. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • Are the two “species” in question what we call “good biological species”?

  32. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • Are the two “species” in question good biological species? • Maybe, maybe not…

  33. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • If two described species are shown to be reproductively compatible, frequently, consistently, and under natural conditions, they are “synonymized”…

  34. Reproductive isolating mechanisms The yellow-rumped warbler was originally described as three separate species: The yellow-rumped warbler, the Myrtle warbler, and the Audubon’s warbler Yellow-rumped warbler

  35. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • Two described species may occasionally hybridize under natural conditions, but in general they are “good species” and maintain reproductive isolation

  36. Reproductive isolating mechanisms Darwin’s medium ground finch Darwin’s small ground finch

  37. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • Two described species may occasionally hybridize under natural conditions, but in general they are “good species” and maintain reproductive isolation • Hybridization may lead to transfer of genes from one species to another

  38. Reproductive isolating mechanisms • Hybridization without reproductive disadvantage… • Two described species may occasionally hybridize under natural conditions, but in general they are “good species” and maintain reproductive isolation • Hybridization may lead to transfer of genes from one species to another • This transfer is called “introgression”

  39. Speciation mechanisms • Speciation is… • …the evolution of reproductive isolation between once-interbreeding populations • How does reproductive isolation evolve? • In most situations, speciation requires geographic isolation of once-interbreeding populations

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