1. Speciation and Macroevolution
Chapter 20

2. Learning Objective 1 What is the biological species concept?
List two potential problems with the concept

3. Biological Species Concept
one or more populations
members interbreed in nature
produce fertile offspring
do not interbreed with different species

4. Sterile Hybrid

5. Problems
Biological species concept applies only to sexually reproducing organisms
Individuals assigned to different species may occasionally successfully interbreed

6. KEY CONCEPTS
According to the biological species concept, a species consists of individuals that can successfully interbreed with one another but not with individuals from other species

7. Learning Objective 2
What is the significance of reproductive isolating mechanisms?
Distinguish among different prezygotic and postzygotic barriers

8. Reproductive Isolating Mechanisms
Restrict gene flow between species
Prezygotic barriers
prevent fertilization from taking place
Postzygotic barriers
prevent gene flow after fertilization has taken place (reproductive isolating mechanisms)

9. Prezygotic Barriers (1)
Temporal isolation
two species reproduce at different times of day, season, or year
Habitat isolation
two closely related species live and breed in different habitats in same geographic area

10. Temporal Isolation

11. Figure 20.2: Temporal isolation in wood and leopard frogs.
Fig. 20-2a, p. 430

12. Figure 20.2: Temporal isolation in wood and leopard frogs.
Fig. 20-2b, p. 430

13. Wood frog Leopard frog Mating activity March 1 April 1 May 1
Figure 20.2: Temporal isolation in wood and leopard frogs.
March 1
April 1
May 1
Fig. 20-2c, p. 430

14. Insert “Temporal isolation among cicadas”
temporal_isolation.swf

15. Prezygotic Barriers (2)
Behavioral isolation
distinctive courtship behaviors prevent mating between species
Mechanical isolation
incompatible structural differences in reproductive organs of similar species

16. Behavioral Isolation

17. Mechanical Isolation

18. Prezygotic Barriers (3)
Gametic isolation
gametes from different species are incompatible because of molecular and chemical differences

19. Postzygotic Barriers (1)
Hybrid inviability
interspecific embryos die during development
Hybrid sterility
prevents interspecific hybrids that survive to adulthood from reproducing successfully

20. Hybrid Sterility

21. Postzygotic Barriers (2)
Hybrid breakdown
prevents offspring of hybrids that survive to adulthood and successfully reproduce from reproducing beyond one or a few generations

22. KEY CONCEPTS
The evolution of different species begins with reproductive isolation, in which two populations are no longer able to interbreed successfully

23. Insert “Reproductive isolating mechanisms”
isolating_mechanisms_m.swf

24. Explore reproductive isolation by clicking on the figures in ThomsonNOW

25. Learning Objective 3
What is allopatric speciation?
Give an example

26. Allopatric Speciation (1)
Evolution of a new species
from ancestral population
Population becomes geographically isolated from rest of species
subsequently diverges

27. Allopatric Speciation (2)
More likely to occur if original isolated population is small
makes genetic drift more significant
Examples:
Death Valley pupfishes
Kaibab squirrels
Porto Santo rabbits

28. Allopatric Speciation

29. KEY CONCEPTS
In allopatric speciation, populations diverge into different species due to geographic isolation, or physical separation

30. Insert “Allopatric speciation on an archipelago”
archipelago.swf

31. Explore allopatric speciation by clicking on the figures in ThomsonNOW.

32. Learning Objective 4 What is sympatric speciation?
Give plant and animal examples

33. Sympatric Speciation Does not require geographic isolation
More common in plants than animals

34. Sympatric Speciation in Plants
Usually results from allopolyploidy
polyploid individual (>2 sets of chromosomes) is hybrid derived from two species
Examples:
kew primroses
hemp nettles

35. Allopolyploidy in Plants

36. Species A Species B 2 n = 6 2 n = 4 P generation n = 3 n = 2 Gametes
Figure 20.9: Sympatric speciation by allopolyploidy in plants.
When two species (designated the P generation) successfully interbreed, the interspecific hybrid offspring (the F1 generation) are almost always sterile (bottom left). If the chromosomes double, proper synapsis and segregation of the chromosomes can occur and viable gametes may be produced (bottom right). (Unduplicated chromosomes are shown for clarity.)
Hybrid AB
F1 generation
Fig. 20-9a, p. 435

37. No doubling of chromosome number Doubling of chromosome number
Chromosomes either cannot pair or go through erratic meiosis
Pairing now possible
during meiosis
n = 5
Figure 20.9: Sympatric speciation by allopolyploidy in plants.
When two species (designated the P generation) successfully interbreed, the interspecific hybrid offspring (the F1 generation) are almost always sterile (bottom left). If the chromosomes double, proper synapsis and segregation of the chromosomes can occur and viable gametes may be produced (bottom right). (Unduplicated chromosomes are shown for clarity.)
No gametes or sterile gametes — no sexual reproduction possible
Viable gametes — sexual reproduction possible (self-fertilization)
Fig. 20-9b, p. 435

38. No doubling of chromosome number
Species A
Species B
P generation
2 n = 6
2 n = 4
n = 3
n = 2
Gametes
Hybrid AB
F1 generation
No doubling of chromosome number
Chromosomes either cannot pair or go through erratic meiosis
Doubling of chromosome number
2 n = 10
Figure 20.9: Sympatric speciation by allopolyploidy in plants.
When two species (designated the P generation) successfully interbreed, the interspecific hybrid offspring (the F1 generation) are almost always sterile (bottom left). If the chromosomes double, proper synapsis and segregation of the chromosomes can occur and viable gametes may be produced (bottom right). (Unduplicated chromosomes are shown for clarity.)
Pairing now possible
during meiosis
n = 5
Viable gametes — sexual reproduction possible (self-fertilization)
No gametes or sterile gametes — no sexual reproduction possible
Stepped Art
Fig. 20-9b, p. 435

39. Sympatric Speciation

40. Sympatric Speciation in Animals
Fruit maggot flies

41. Sympatric Speciation in Animals
Cichlids

42. Figure 20.12: Color variation in Lake Victoria cichlids.
Some evidence suggests that changes in male coloration may be the first step in speciation of Lake Victoria cichlids. Later, other traits, including ecological characteristics, diverge. Female cichlids generally have cryptic coloration; their drab colors help them blend into their surroundings.
Fig a, p. 437

43. Figure 20.12: Color variation in Lake Victoria cichlids.
Some evidence suggests that changes in male coloration may be the first step in speciation of Lake Victoria cichlids. Later, other traits, including ecological characteristics, diverge. Female cichlids generally have cryptic coloration; their drab colors help them blend into their surroundings.
Fig b, p. 437

44. Figure 20.12: Color variation in Lake Victoria cichlids.
Some evidence suggests that changes in male coloration may be the first step in speciation of Lake Victoria cichlids. Later, other traits, including ecological characteristics, diverge. Female cichlids generally have cryptic coloration; their drab colors help them blend into their surroundings.
Fig c, p. 437

45. KEY CONCEPTS
In sympatric speciation, populations become reproductively isolated from one another despite living in the same geographic area

46. Insert “Sympatric speciation in wheat”
wheat_speciation.swf

47. Explore sympatric speciation by clicking on the figure in ThomsonNOW.

48. Learning Objective 5
Debate the pace of evolution by representing the views of either punctuated equilibrium or gradualism

49. Evolution Punctuated equilibrium model Gradualism model
evolution proceeds in spurts
short periods of active speciation interspersed with long periods of stasis
Gradualism model
populations slowly diverge from one another by accumulation of adaptive characteristics

50. Punctuated Equilibrium and Gradualism

51. Extinction of original species
Slow, gradual changes
Stasis
Stasis
Stasis
Time
Divergence is sudden, with rapid changes
Time
Divergence is gradual
Stasis (little
change)
Figure 20.13: Punctuated equilibrium and gradualism.
In this figure, structural changes in the lizards are represented by changes in skin color.
Structural changes
Structural changes
Fig , p. 438

52. KEY CONCEPTS
Speciation may require millions of years but sometimes occurs much more quickly

53. Learning Objective 6
What is macroevolution?

54. Macroevolution Large-scale phenotypic changes in populations
in taxonomic groups species level and higher
new species, genera, families, orders, classes, phyla, kingdoms, or domains

55. KEY CONCEPTS
The evolution of species and higher taxa is known as macroevolution

56. Learning Objective 7
Discuss novel features of macroevolution, including preadaptations, allometric growth, and paedomorphosis

57. Macroevolution Includes evolutionary novelties
due to changes during development
Slight changes in regulatory genes
cause major structural changes in organism

58. Preadaptations Structures originally fulfilled one role
changed and adapted for different role
Example: feathers

59. Allometric Growth Varied rates of growth for different parts of body
causes overall changes in shape of organism
Examples:
ocean sunfish
male fiddler crab

60. Allometric Growth
Ocean sunfish

61. Newly hatched ocean sunfish Adult ocean sunfish
Tail
approx. 1 mm
Newly hatched ocean sunfish
Adult
ocean sunfish
Figure 20.14: Allometric growth in the ocean sunfish.
The tail end of an ocean sunfish (Mola mola) grows faster than the head end, resulting in the unique shape of the adult.
Fig a, p. 440

62. Figure 20.14: Allometric growth in the ocean sunfish.
The tail end of an ocean sunfish (Mola mola) grows faster than the head end, resulting in the unique shape of the adult.
Fig b, p. 440

63. Figure 20.14: Allometric growth in the ocean sunfish.
The tail end of an ocean sunfish (Mola mola) grows faster than the head end, resulting in the unique shape of the adult.
Fig b, p. 440

64. Paedomorphosis Juvenile characteristics retained in adult
due to changes in timing of development
Example: adult axolotl salamanders
with external gills and tail fins

65. Paedomorphosis
Salamander

66. Learning Objective 8
What is the macroevolutionary significance of adaptive radiation and extinction?

67. Adaptive Radiation (1)
Diversification of ancestral species into many new species
Adaptive zones
new ecological opportunities not exploited by ancestral organism

68. Adaptive Radiation (2) When many adaptive zones are empty
colonizing species diversify and exploit them
Example: Hawaiian honeycreepers and silverswords
after ancestors colonized Hawaiian Islands

69. Adaptive Radiation
Hawaiian honeycreepers

70. Rips away bark to find insects Kauai Sips flower nectar
Maui parrot bill
‘I‘iwi
Oahu
Forages among
leaves and branches
Maui creeper
Maui
Chisels holes in bark to get insects
Extinct
Habits unknown
Akiapolaau
Ula-ai-hawane
Extinct Sipped flower nectar
Hawaii
Figure 20.16: Adaptive radiation in Hawaiian honeycreepers.
Compare the various beak shapes and methods of obtaining food. Many honeycreeper species are now extinct or nearing extinction as a result of human activities, including the destruction of habitat and the introduction of predators such as rats, dogs, and pigs.
Black mamo
Picks food from cracks in the bark
Sips flower nectar
Akialoa
Apapane
Feeds on snails and invertebrates
Sips flower nectar
Poo-uli
Crested honeycreeper
Fig , p. 441

71. Adaptive Radiation
Hawaiian silverswords

72. Extinction (1) Death of a species When species become extinct
adaptive zones they occupied become vacant
allows other species to evolve and fill zones

73. Extinction (2) Background extinction Mass extinction
continuous, low-level extinction of species
Mass extinction
extinction of numerous species, higher taxonomic groups
in both terrestrial and marine environments

74. Mass Extinction

75. Pterosaurs (flying reptiles, extinct)
Ornithischians (dinosaurs, extinct)
Crocodilians (alligators, crocodiles)
Saurischians (dinosaurs, extinct)
Birds
Common ancestor of birds and saurischians
Figure 20.18: Mass extinction of the archosaurs.
(a) Cladogram of the descendants of archosaurs, reptiles that were the ancestors of the dinosaurs. (b) At the end of the Cretaceous period, approximately 65 mya, a mass extinction of many organisms, including the remaining dinosaurs, occurred. (Dinosaurs had already been declining in diversity throughout the latter part of the Cretaceous period.) The only archosauran lines to survive were crocodiles and birds.
Archosaur common ancestor
Fig a, p. 443

76. Fig. 20-18b, p. 443 Figure 20.18: Mass extinction of the archosaurs.
(a) Cladogram of the descendants of archosaurs, reptiles that were the ancestors of the dinosaurs. (b) At the end of the Cretaceous period, approximately 65 mya, a mass extinction of many organisms, including the remaining dinosaurs, occurred. (Dinosaurs had already been declining in diversity throughout the latter part of the Cretaceous period.) The only archosauran lines to survive were crocodiles and birds.
Fig b, p. 443

77. Theropods (carnivorous saurischians)
Paleozoic
Mesozoic
Cenozoic
Permian
Triassic
Jurassic
Cretaceous
Tertiary / Quaternary
Theropods (carnivorous saurischians)
Birds
Sauropods (herbivorous saurischians)
Archosaurs
Common ancestor
Figure 20.18: Mass extinction of the archosaurs.
(a) Cladogram of the descendants of archosaurs, reptiles that were the ancestors of the dinosaurs. (b) At the end of the Cretaceous period, approximately 65 mya, a mass extinction of many organisms, including the remaining dinosaurs, occurred. (Dinosaurs had already been declining in diversity throughout the latter part of the Cretaceous period.) The only archosauran lines to survive were crocodiles and birds.
Stegosaurs and other ornithischians
Pterosaurs
Crocodilians
Crocodiles
Fig b, p. 443