Chapter 24:<br />The Origin of Species<br />1<br />
Flightless Cormorant (Phalacrocoraxharrisi)<br />Plants and animals were found on the Galapagos Islands that were not foun...
Key Terms:<br />Speciation, the origin of new species, is at the focal point of evolutionary theory <br />Microevolutionco...
Concept 24.1<br />The biological species concept emphasizes reproductive isolation<br />4<br />
Species is a Latin word meaning “kind” or “appearance”<br />Difficult to clearly define.<br />5<br />
Biological Species Concept<br />A species is a group of populations whose members have the potential to interbreed in natu...
7<br />
8<br />
Reproductive Isolation<br />Existence of biological barriers that prevent two species from producing viable, fertile offsp...
Hybrids<br />Mule – (M) Donkey/(F) Horse<br />Liger – (M) Lion/(F) Tiger<br />10<br />
Prezygotic Barriers<br />Block fertilization:<br />Preventing the successful completion of mating.<br />Hinders fertilizat...
Habitat Isolation<br />Species rarely encounter each other, or not at all.<br />Occupy different habitats.<br />Isolated b...
13<br />
14<br />
Limitations of Biological Species Concept<br />Cannot be applied to fossils or asexual organisms.<br />15<br />
Other “Definitions” of Species<br />Morphological species concept:<br />Defines species by structural features<br />Ecolog...
You should now be able to:<br />Define and discuss the limitations of the four species concepts<br />Describe and provide ...
Concept 24.2<br />Speciation can take place with or without geographic separation<br />18<br />
19<br />
20<br />Antelope squirrels on opposite rims of the Grand Canyon.<br />More Geographic Barriers = More Species<br />
21<br />GENERALLY: As distance between population increases, reproductive isolation increases.<br />
Sympatric Speciation<br />Geographically overlapping populations.<br />Polyploidy is the presence of extra sets of chromos...
Sympatric speciation by autopolyploidy in plants<br />23<br />
Allopolyploid<br />24<br />Aspecies with multiple sets of chromosomes derived from different species<br />
Polyploidy is much more common in plants than in animals<br />Many important crops (oats, cotton, potatoes, tobacco, and w...
Habitat Differentiation<br />Sympatric speciation can also result from the appearance of new ecological niches<br />For ex...
Sexual Selection<br />Sexual selection can drive sympatric speciation<br />Sexual selection for mates of different colors ...
28<br />
Allopatric and Sympatric Speciation: A Review<br />In allopatric speciation, geographic isolation restricts gene flow betw...
You should now be able to:<br />Distinguish between and provide examples of allopatric and sympatric speciation<br />Expla...
Concept 24.3<br />Hybrid zones provide opportunities to study factors that cause reproductive isolation<br />31<br />
A hybrid zone is a region in which members of different species mate and produce hybrids<br />32<br />
Patterns Within Hybrid Zones<br />A hybrid zone can occur in a single band where adjacent species meet<br />Hybrids often ...
34<br />
Hybrid Zones over Time<br />When closely related species meet in a hybrid zone, there are three possible outcomes:<br />St...
36<br />
Reinforcement: Strengthening Reproductive Barriers<br />The reinforcement of barriers occurs when hybrids are less fit tha...
38<br />
39<br />
Fusion: Weakening Reproductive Barriers<br />If hybrids are as fit as parents, there can be substantial gene flow between ...
41<br />
Stability: Continued Formation of Hybrid Individuals<br />Extensive gene flow from outside the hybrid zone can overwhelm s...
You should now be able to:<br />Define the term hybrid zone and describe three outcomes for hybrid zones over time<br />43...
Concept 24.4<br />Speciation can occur rapidly or slowly and can result from changes in few or many genes<br />44<br />
Patterns in the Fossil Record<br />Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe...
46<br />
Speciation Rates<br />The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation c...
Rapid speciation in a sunflower hybrid zone<br />48<br />
Genetics of Speciation<br />Depending on the species in question, speciation might require the change of only a single all...
Single Gene Speciation<br />50<br />
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OHHS AP Biology Chapter 24 (Class Presentation)

  1. 1. Chapter 24:<br />The Origin of Species<br />1<br />
  2. 2. Flightless Cormorant (Phalacrocoraxharrisi)<br />Plants and animals were found on the Galapagos Islands that were not found anywhere else on Earth.<br />2<br />
  3. 3. Key Terms:<br />Speciation, the origin of new species, is at the focal point of evolutionary theory <br />Microevolutionconsists of adaptations that evolve within a population, confined to one gene pool<br />Macroevolution refers to evolutionary change above the species level<br />3<br />
  4. 4. Concept 24.1<br />The biological species concept emphasizes reproductive isolation<br />4<br />
  5. 5. Species is a Latin word meaning “kind” or “appearance”<br />Difficult to clearly define.<br />5<br />
  6. 6. Biological Species Concept<br />A species is 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<br />6<br />
  7. 7. 7<br />
  8. 8. 8<br />
  9. 9. Reproductive Isolation<br />Existence of biological barriers that prevent two species from producing viable, fertile offspring.<br />Can be factors before or after fertilization.<br />9<br />
  10. 10. Hybrids<br />Mule – (M) Donkey/(F) Horse<br />Liger – (M) Lion/(F) Tiger<br />10<br />
  11. 11. Prezygotic Barriers<br />Block fertilization:<br />Preventing the successful completion of mating.<br />Hinders fertilization if mating is successful.<br />11<br />
  12. 12. Habitat Isolation<br />Species rarely encounter each other, or not at all.<br />Occupy different habitats.<br />Isolated by physical barriers.<br />12<br />
  13. 13. 13<br />
  14. 14. 14<br />
  15. 15. Limitations of Biological Species Concept<br />Cannot be applied to fossils or asexual organisms.<br />15<br />
  16. 16. Other “Definitions” of Species<br />Morphological species concept:<br />Defines species by structural features<br />Ecological species concept:<br />Views a species in terms of its ecological niche<br />Phylogenetic species concept: <br />Defines a species as the smallest group of individuals on a phylogenetic tree<br />16<br />
  17. 17. You should now be able to:<br />Define and discuss the limitations of the four species concepts<br />Describe and provide examples of prezygotic and postzygotic reproductive barriers<br />17<br />
  18. 18. Concept 24.2<br />Speciation can take place with or without geographic separation<br />18<br />
  19. 19. 19<br />
  20. 20. 20<br />Antelope squirrels on opposite rims of the Grand Canyon.<br />More Geographic Barriers = More Species<br />
  21. 21. 21<br />GENERALLY: As distance between population increases, reproductive isolation increases.<br />
  22. 22. Sympatric Speciation<br />Geographically overlapping populations.<br />Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division<br />An autopolyploid is an individual with more than two chromosome sets, derived from one species<br />22<br />
  23. 23. Sympatric speciation by autopolyploidy in plants<br />23<br />
  24. 24. Allopolyploid<br />24<br />Aspecies with multiple sets of chromosomes derived from different species<br />
  25. 25. Polyploidy is much more common in plants than in animals<br />Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids<br />25<br />
  26. 26. Habitat Differentiation<br />Sympatric speciation can also result from the appearance of new ecological niches<br />For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees<br />26<br />
  27. 27. Sexual Selection<br />Sexual selection can drive sympatric speciation<br />Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria <br />27<br />
  28. 28. 28<br />
  29. 29. Allopatric and Sympatric Speciation: A Review<br />In allopatric speciation, geographic isolation restricts gene flow between populations<br />Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations<br />In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species<br />Sympatric speciation can result from polyploidy, natural selection, or sexual selection<br />29<br />
  30. 30. You should now be able to:<br />Distinguish between and provide examples of allopatric and sympatric speciation<br />Explain how polyploidy can cause reproductive isolation<br />30<br />
  31. 31. Concept 24.3<br />Hybrid zones provide opportunities to study factors that cause reproductive isolation<br />31<br />
  32. 32. A hybrid zone is a region in which members of different species mate and produce hybrids<br />32<br />
  33. 33. Patterns Within Hybrid Zones<br />A hybrid zone can occur in a single band where adjacent species meet<br />Hybrids often have reduced fitness compared with parent species<br />The distribution of hybrid zones can be more complex if parent species are found in multiple habitats within the same region<br />33<br />
  34. 34. 34<br />
  35. 35. Hybrid Zones over Time<br />When closely related species meet in a hybrid zone, there are three possible outcomes:<br />Strengthening of reproductive barriers<br />Weakening of reproductive barriers<br />Continued formation of hybrid individuals<br />35<br />
  36. 36. 36<br />
  37. 37. Reinforcement: Strengthening Reproductive Barriers<br />The reinforcement of barriers occurs when hybrids are less fit than the parent species<br />Over time, the rate of hybridization decreases<br />Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species<br />37<br />
  38. 38. 38<br />
  39. 39. 39<br />
  40. 40. Fusion: Weakening Reproductive Barriers<br />If hybrids are as fit as parents, there can be substantial gene flow between species<br />If gene flow is great enough, the parent species can fuse into a single species<br />40<br />
  41. 41. 41<br />
  42. 42. Stability: Continued Formation of Hybrid Individuals<br />Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone<br />In cases where hybrids have increased fitness, local extinctions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers<br />42<br />
  43. 43. You should now be able to:<br />Define the term hybrid zone and describe three outcomes for hybrid zones over time<br />43<br />
  44. 44. Concept 24.4<br />Speciation can occur rapidly or slowly and can result from changes in few or many genes<br />44<br />
  45. 45. Patterns in the Fossil Record<br />Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change<br />45<br />
  46. 46. 46<br />
  47. 47. Speciation Rates<br />The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid<br />The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years<br />47<br />
  48. 48. Rapid speciation in a sunflower hybrid zone<br />48<br />
  49. 49. Genetics of Speciation<br />Depending on the species in question, speciation might require the change of only a single allele or many alleles<br />49<br />
  50. 50. Single Gene Speciation<br />50<br />
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