1. Chapter 24: The Origin of Species

2. Question? What is a species?
Comment - Evolution theory must also explain how species originate.

3. Question
How many species of African Violets are here?

4. Two Concepts of Species
1. Morphospecies
2. Biological Species

5. Morphospecies
Organisms with very similar morphology or physical form.

6. Problem
Where does extensive phenotype variation fit?

7. Two Schools
1. Splitters - Break apart species into new ones on the basis of small phenotype changes.
2. Lumpers - Group many phenotype variants into one species.

8. Biological Species
A group of organisms that could interbreed in nature and produce fertile offspring.

9. Key Points
Could interbreed.
Fertile offspring.

10. Morphospecies & Biological Species
Often overlap.
Serve different purposes.

11. African Violets 15+ species 5+ varieties (natural hybrids)
50,000 cultivars

12. Example Problem S. magungensis Cluster: S. Magungensis
S. magungensis var. minima
S. magungensis var. occidentalis

13. Current Placement One species and two varieties. However :
Not all live in the same habitat.
Not all flower under the same temperatures.

14. Possible New Placement
Two species and one variety.
S. magungensis var. occidentalis may be a new species.

15. Speciation Requires: 1. Variation in the population. 2. Selection.
3. Isolation.

16. Reproductive Barriers
Serve to isolate a populations from other gene pools.
Create and maintain “species”.

17. Main Types of Barriers Prezygotic - Prevent mating or fertilization.
Postzygotic - Prevent viable, fertile offspring.

18. Prezygotic - Types 1. Habitat Isolation 2. Behavioral Isolation
3. Temporal Isolation
4. Mechanical Isolation
5. Gametic Isolation

19. Habitat Isolation
Populations live in different habitats or ecological niches.
Ex – mountains vs lowlands.

20. Behavioral Isolation Mating or courtship behaviors different.
Different sexual attractions operating.
Ex – songs and dances in birds.

21. Temporal Isolation Breeding seasons or time of day different.
Ex – flowers open in morning or evening.

22. Mechanical Isolation
Structural differences that prevent gamete transfer.
Ex – anthers not positioned to put pollen on a bee, but will put pollen on a bird.

23. Gametic Isolation Gametes fail to attract each other and fuse.
Ex – chemical markers on egg and sperm fail to match.

24. Postzygotic Types 1. Reduced Hybrid Viability
2. Reduced Hybrid Fertility
3. Hybrid Breakdown

25. Reduced Hybrid Viability
Zygote fails to develop or mature.
Ex – when different species of frogs hybridize.

26. Reduced Hybrid Fertility
Hybrids are viable, but can't reproduce sexually.
Chromosome count often “odd” so meiosis won’t work.
Ex - mules

27. Hybrid Breakdown
Offspring are fertile, but can't compete successfully with the “pure breeds”.
Ex – many plant hybrids

28. Introgression
Transfer of alleles between two species, but only a partial gene flow.
Result – Some intermixing of genes between two species.

29. Importance
A possible mechanism for gene flow between similar species.

30. Question Actively evolving species like Quercus.
Good isolation mechanisms or poor ones?
Isolation mechanisms may not have fully developed yet.

31. Other Concepts of Species
1. Recognition Species Concept
2. Cohesion Species Concept
3. Ecological Species Concept
4. Evolutionary Species Concept

32. Recognition Species Concept
Species are defined by the ability of the individuals in the population to recognize certain characteristics in each other.
Ex – mate recognition

33. Cohesion Species Concept
Emphasizes cohesion of phenotypes (complex of genes and set of adaptations).

34. Ecological Species Concept
Emphasizes a species role or function in the environment.

35. Evolutionary Species Concept
Emphasizes evolutionary lineages and ecological roles.

36. Comment
AP exam will focus on morphological and biological species concepts.

37. Modes of Speciation 1. Allopatric Speciation 2. Sympatric Speciation
Both work through a block of gene flow between two populations.

39. Allopatric Speciation
Allopatric = other homeland
Ancestral population split by a geographical feature.
Comment – the size of the geographical feature may be very large or small.

40. Example Pupfish populations in Death Valley.
Generally happens when a specie’s range shrinks for some reason.

41. Another Example

42. Conditions Favoring Allopatric Speciation
1. Founder's Effect - with the peripheral isolate.
2. Genetic Drift – gives the isolate population variation as compared to the original population.

43. Conditions Favoring Allopatric Speciation
3. Selection pressure on the isolate differs from the parent population.

44. Result Gene pool of isolate changes from the parent population.
New Species can form.

45. Comment
Populations separated by geographical barriers may not evolve much.
Ex - Pacific and Atlantic Ocean populations separated by the Panama Isthmus.

46. Examples Fish - 72 identical kinds. Crabs - 25 identical kinds.
Echinoderms - 25 identical kinds.

47. Adaptive Radiation
Rapid emergence of several species from a common ancestor.
Common in island and mountain top populations or other “empty” environments.
Ex – Galapagos Finches

48. Mechanism Resources are temporarily infinite. Most offspring survive.
Result - little Natural Selection and the gene pool can become very diverse.

49. When the Environment Saturates
Natural Selection resumes.
New species form rapidly if isolation mechanisms work.

50. Sympatric Speciation Sympatric = same homeland
New species arise within the range of parent populations.
Can occur In a single generation.

52. Plants
Polyploids may cause new species because the change in chromosome number creates postzygotic barriers.

53. Polyploid Types
1. Autopolyploid - when a species doubles its chromosome number from 2N to 4N.
2. Allopolyploid - formed as a polyploid hybrid between two species.
Ex: wheat

54. Autopolyploid

55. Allopolyploid

56. Animals
Don't form polyploids and will use other mechanisms.

57. Gradualism Evolution Darwinian style evolution.
Small gradual changes over long periods time.

58. Gradualism Predicts: Long periods of time are needed for evolution.
Fossils should show continuous links.

59. Problem
Gradualism doesn’t fit the fossil record very well. (too many “gaps”).

60. Punctuated Evolution New theory on the “pacing” of evolution.
Elridge and Gould – 1972.

61. Punctuated Equilibrium
Evolution has two speeds of change:
Gradualism or slow change
Rapid bursts of speciation

62. Predictions
Speciation can occur over a very short period of time (1 to 1000 generations).
Fossil record will have gaps or missing links.

64. Predictions
New species will appear in the fossil record without connecting links or intermediate forms.
Established species will show gradual changes over long periods of time.

65. Possible Mechanism
Adaptive Radiation, especially after mass extinction events allow new species to originate.
Saturated environments favor gradual changes in the current species.

66. Comment Punctuated Equilibrium is the newest ”Evolution Theory”.
Best explanation of fossil record evidence to date.

67. Origin of Evolutionary Novelty
How do macroevolution changes originate?
Several ideas discussed in textbook.
Exaptation
Heterochrony
Homeosis

68. Exaptation
When a structure that was adapted for one context is co-opted for another function.
Ex. – feathers and flying

69. Heterochrony Changes in the timing or rate of development.
Allometric Growth
Paedomorphsis

70. 1. Allometric Growth – changes in the relative rates of growth of various parts of the body.
Ex. – skull growth in primates

72. 2. Paedomorphosis – when an adult retains features that are present in the juvenile form.
Ex. – gills in adult salamanders

74. Homeosis
Changes in the basic body design or arrangement of body parts.
Ex. – Hox gene clusters that gave rise to vertebrates from invertebrates.

76. Evolutionary Trends
Evolution is not goal oriented. It does not produce “perfect” species.

78. Future of Evolution ?
Look for new theories and ideas to be developed, especially from new fossil finds and from molecular (DNA) evidence.

79. Summary Be able to discuss the main theories of what is a “species”.
Know various reproductive barriers and examples.

80. Summary Know allopatric and sympatric speciation.
Be able to discuss gradualism and punctuated equilibrium theories.

81. Summary
Recognize various ideas about the origin of evolutionary novelties.