1) The document summarizes key concepts from Chapter 24 of Campbell Biology about the origin of species. It discusses allopatric and sympatric speciation, describing how new species can form with or without geographic separation between populations. 2) Reproductive isolation is formed by prezygotic barriers that prevent mating or fertilization, and postzygotic barriers that result in non-viable or infertile hybrid offspring. 3) Examples are given of allopatric speciation including mosquitofish that evolved in isolated ponds, and snapping shrimp separated when the Isthmus of Panama formed.

1. LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
The Origin of Species
Chapter 24

2. Overview: That “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on Earth
© 2011 Pearson Education, Inc.
Video: Galápagos Tortoise

3. Figure 24.1

4. • Speciation, the origin of new species, is at the
focal point of evolutionary theory
• Evolutionary theory must explain how new species
originate and how populations evolve
• Microevolution consists of changes in allele
frequency in a population over time
• Macroevolution refers to broad patterns of
evolutionary change above the species level
© 2011 Pearson Education, Inc.
Animation: Macroevolution

5. Concept 24.1: The biological species
concept emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance”
• Biologists compare morphology, physiology,
biochemistry, and DNA sequences when
grouping organisms
© 2011 Pearson Education, Inc.

6. The Biological Species Concept
• The biological species concept states that 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
• Gene flow between populations holds the
phenotype of a population together
© 2011 Pearson Education, Inc.

7. Figure 24.2
(a) Similarity between different species
(b) Diversity within a species

8. Figure 24.2a
(a) Similarity between different species

9. Figure 24.2b
(b) Diversity within a species

10. Figure 24.2c

11. Figure 24.2d

12. Figure 24.2e

13. Figure 24.2f

14. Figure 24.2g

15. Figure 24.2h

16. Figure 24.2i

17. Figure 24.2j

18. Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two
species from producing viable, fertile offspring
• Hybrids are the offspring of crosses between
different species
• Reproductive isolation can be classified by
whether factors act before or after fertilization
© 2011 Pearson Education, Inc.

19. Figure 24.3_a
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
Individuals
of
different
species
MATING
ATTEMPT FERTILIZATION
VIABLE,
FERTILE
OFFSPRING
Postzygotic barriers
(a) (c) (e)
(d)
(b)
(g)
(k)
(h) (i)
(j)
(l)(f)

20. Figure 24.3_b
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
Isolation
Individuals
of
different
species
MATING
ATTEMPT FERTILIZATION
(a) (c) (e) (f)
(b)
(g)
(d)

21. Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
FERTILIZATION
VIABLE,
FERTILE
OFFSPRING
Postzygotic barriers
(k)
(h) (i)
(j)
(l)
Figure 24.3_c

22. • Prezygotic barriers block fertilization from
occurring by:
– Impeding different species from attempting to
mate
– Preventing the successful completion of mating
– Hindering fertilization if mating is successful
© 2011 Pearson Education, Inc.

23. Figure 24.3a
(a)

24. Figure 24.3b
(b)

25. • Habitat isolation: Two species encounter each
other rarely, or not at all, because they occupy
different habitats, even though not isolated by
physical barriers
© 2011 Pearson Education, Inc.

26. Figure 24.3c
(c)

27. Figure 24.3d
(d)

28. • Temporal isolation: Species that breed at
different times of the day, different seasons,
or different years cannot mix their gametes
© 2011 Pearson Education, Inc.

29. Figure 24.3e
(e)

30. • Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective
barriers
© 2011 Pearson Education, Inc.
Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Albatross Courtship Ritual

31. Figure 24.3f
(f)

32. • Mechanical isolation: Morphological differences
can prevent successful mating
© 2011 Pearson Education, Inc.

33. Figure 24.3g
(g)

34. • Gametic Isolation: Sperm of one species may not
be able to fertilize eggs of another species
© 2011 Pearson Education, Inc.

35. • Postzygotic barriers prevent the hybrid zygote
from developing into a viable, fertile adult:
– Reduced hybrid viability
– Reduced hybrid fertility
– Hybrid breakdown
© 2011 Pearson Education, Inc.

36. Figure 24.3h
(h)

37. • Reduced hybrid viability: Genes of the different
parent species may interact and impair the
hybrid’s development
© 2011 Pearson Education, Inc.

38. Figure 24.3i
(i)

39. Figure 24.3j
(j)

40. Figure 24.3k
(k)

41. • Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile
© 2011 Pearson Education, Inc.

42. Figure 24.3l
(l)

43. • Hybrid breakdown: Some first-generation hybrids
are fertile, but when they mate with another
species or with either parent species, offspring of
the next generation are feeble or sterile
© 2011 Pearson Education, Inc.

44. Limitations of the Biological Species Concept
• The biological species concept cannot be
applied to fossils or asexual organisms
(including all prokaryotes)
• The biological species concept emphasizes
absence of gene flow
• However, gene flow can occur between
distinct species
– For example, grizzly bears and polar bears
can mate to produce “grolar bears”
© 2011 Pearson Education, Inc.

45. Figure 24.4
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear”

46. Figure 24.4a
Grizzly bear (U. arctos)

47. Figure 24.4b
Polar bear (U. maritimus)

48. Figure 24.4c
Hybrid “grolar bear”

49. Other Definitions of Species
• Other species concepts emphasize the unity within
a species rather than the separateness of different
species
• The morphological species concept defines a
species by structural features
– It applies to sexual and asexual species but relies
on subjective criteria
© 2011 Pearson Education, Inc.

50. • The ecological species concept views a species
in terms of its ecological niche
– It applies to sexual and asexual species and
emphasizes the role of disruptive selection
• The phylogenetic species concept defines a
species as the smallest group of individuals on a
phylogenetic tree
– It applies to sexual and asexual species, but it can
be difficult to determine the degree of difference
required for separate species
© 2011 Pearson Education, Inc.

51. Concept 24.2: Speciation can take place
with or without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
– Sympatric speciation
© 2011 Pearson Education, Inc.

52. Figure 24.5
(a) (b)Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.

53. Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is
interrupted or reduced when a population is
divided into geographically isolated
subpopulations
– For example, the flightless cormorant of the
Galápagos likely originated from a flying
species on the mainland
© 2011 Pearson Education, Inc.

54. The Process of Allopatric Speciation
• The definition of barrier depends on the ability of a
population to disperse
– For example, a canyon may create a barrier for
small rodents, but not birds, coyotes, or pollen
© 2011 Pearson Education, Inc.

55. Figure 24.6
A. harrisii A. leucurus

56. Figure 24.6a
A. harrisii

57. Figure 24.6b
A. leucurus

58. Figure 24.6c

59. • Separate populations may evolve independently
through mutation, natural selection, and genetic
drift
• Reproductive isolation may arise as a result of
genetic divergence
– For example, mosquitofish in the Bahamas
comprise several isolated populations in different
ponds
© 2011 Pearson Education, Inc.

60. Figure 24.7
(a) Under high predation (b) Under low predation

61. Figure 24.7a

62. Figure 24.7b

63. Evidence of Allopatric Speciation
• 15 pairs of sibling species of snapping shrimp
(Alpheus) are separated by the Isthmus of
Panama
• These species originated 9 to 13 million years
ago, when the Isthmus of Panama formed and
separated the Atlantic and Pacific waters
© 2011 Pearson Education, Inc.

64. Figure 24.8
A. formosus
Atlantic Ocean
A. nuttingi
Isthmus of Panama
Pacific Ocean
A. panamensis A. millsae

65. Figure 24.8a

66. Figure 24.8b
Atlantic Ocean
Isthmus of Panama
Pacific Ocean

67. Figure 24.8c
A. formosus

68. Figure 24.8d
A. panamensis

69. Figure 24.8e
A. nuttingi

70. Figure 24.8f
A. millsae

71. • Regions with many geographic barriers
typically have more species than do regions
with fewer barriers
• Reproductive isolation between populations
generally increases as the distance between
them increases
– For example, reproductive isolation
increases between dusky salamanders that
live further apart
© 2011 Pearson Education, Inc.

72. Figure 24.9
Degreeofreproductiveisolation
Geographic distance (km)
0 50 100 150 200 250 300
2.0
1.5
1.0
0.5
0

73. • Barriers to reproduction are intrinsic;
separation itself is not a biological barrier
© 2011 Pearson Education, Inc.

74. Figure 24.10
EXPERIMENT
RESULTS
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised
on starch medium
Mating experiments
after 40 generations
Some flies raised on
maltose medium
Female
Starch Maltose
Male
MaltoseStarch
Number of matings
in experimental group
22 9
8 20
Female
Starch
population 1
Male
Starch
population2
Number of matings
in control group
18 15
12 15
Starch
population 2
Starch
population1

75. Figure 24.10a
EXPERIMENT
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised
on starch medium
Mating experiments
after 40 generations
Some flies raised on
maltose medium

76. Figure 24.10b
RESULTS
Female
Starch Maltose
Male
MaltoseStarch
Number of matings
in experimental group
22 9
8 20
Female
Starch
population 1
Male
Starch
population2
Number of matings
in control group
18 15
12 15
Starch
population 2
Starch
population1

77. Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place
in geographically overlapping populations
© 2011 Pearson Education, Inc.

78. Polyploidy
• Polyploidy is the presence of extra sets of
chromosomes due to accidents during cell
division
• Polyploidy is much more common in plants
than in animals
• An autopolyploid is an individual with more
than two chromosome sets, derived from one
species
© 2011 Pearson Education, Inc.

79. • An allopolyploid is a species with multiple
sets of chromosomes derived from different
species
© 2011 Pearson Education, Inc.

80. Figure 24.11-1
Species A
2n = 6
Species B
2n = 4
Normal
gamete
n = 3
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes

81. Figure 24.11-2
Species A
2n = 6
Species B
2n = 4
Normal
gamete
n = 3
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes

82. Figure 24.11-3
Species A
2n = 6
Species B
2n = 4
Normal
gamete
n = 3
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Unreduced gamete
with 7 chromosomes
Normal
gamete
n = 3

83. Figure 24.11-4
Species A
2n = 6
Species B
2n = 4
Normal
gamete
n = 3
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Unreduced gamete
with 7 chromosomes
Normal
gamete
n = 3
New species:
viable fertile hybrid
(allopolyploid) 2n = 10

84. • Many important crops (oats, cotton, potatoes,
tobacco, and wheat) are polyploids
© 2011 Pearson Education, Inc.

85. Habitat Differentiation
• Sympatric speciation can also result from the
appearance of new ecological niches
• For example, the North American maggot fly can
live on native hawthorn trees as well as more
recently introduced apple trees
© 2011 Pearson Education, Inc.

86. Sexual Selection
• Sexual selection can drive sympatric speciation
• Sexual selection for mates of different colors has
likely contributed to speciation in cichlid fish in
Lake Victoria
© 2011 Pearson Education, Inc.

87. Figure 24.12
Normal light
Monochromatic
orange light
P. pundamilia
P. nyererei
EXPERIMENT

88. Figure 24.12a
P. pundamilia
Normal light

89. Figure 24.12b
P. nyererei
Normal light

90. Figure 24.12c
Monochromatic
orange light
P. pundamilia

91. Figure 24.12d
Monochromatic
orange light
P. nyererei

92. Allopatric and Sympatric Speciation:
A Review
• In allopatric speciation, geographic isolation
restricts gene flow between populations
• Reproductive isolation may then arise by natural
selection, genetic drift, or sexual selection in the
isolated populations
• Even if contact is restored between populations,
interbreeding is prevented
© 2011 Pearson Education, Inc.

93. • In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
• Sympatric speciation can result from polyploidy,
natural selection, or sexual selection
© 2011 Pearson Education, Inc.

94. Concept 24.3: Hybrid zones reveal factors
that cause reproductive isolation
• A hybrid zone is a region in which members of
different species mate and produce hybrids
• Hybrids are the result of mating between species
with incomplete reproductive barriers
© 2011 Pearson Education, Inc.

95. Patterns Within Hybrid Zones
• A hybrid zone can occur in a single band where
adjacent species meet
– For example, two species of toad in the genus
Bombina interbreed in a long and narrow hybrid
zone
© 2011 Pearson Education, Inc.

96. Figure 24.13
EUROPE
Yellow-bellied
toad, Bombina
variegata
Fire-bellied
toad range
Hybrid zone
Yellow-bellied
toad range
Fire-bellied toad, Bombina bombina
Frequencyof
B.variegata-specificallele
Yellow-bellied
toad range
Hybrid
zone
Fire-bellied
toad range
Distance from hybrid zone center (km)
40
0.99
0.9
0.5
0.1
0.01
30 20 10 0 10 20

97. Figure 24.13a
EUROPE
Fire-bellied
toad range
Hybrid zone
Yellow-bellied
toad range

98. Figure 24.13b
Frequencyof
B.variegata-specificallele
Yellow-bellied
toad range
Hybrid
zone
Fire-bellied
toad range
Distance from hybrid zone center (km)
40
0.99
0.9
0.5
0.1
0.01
30 20 10 0 10 20

99. Figure 24.13c
Fire-bellied toad, Bombina bombina

100. Figure 24.13d
Yellow-bellied toad, Bombina variegata

101. • Hybrids often have reduced fitness compared with
parent species
• The distribution of hybrid zones can be more
complex if parent species are found in patches
within the same region
© 2011 Pearson Education, Inc.

102. Hybrid Zones over Time
• When closely related species meet in a hybrid
zone, there are three possible outcomes:
– Reinforcement
– Fusion
– Stability
© 2011 Pearson Education, Inc.

103. Figure 24.14-1
Gene flow
Population
Barrier to
gene flow

104. Figure 24.14-2
Gene flow
Population
Barrier to
gene flow
Isolated
population
diverges

105. Figure 24.14-3
Gene flow
Population
Barrier to
gene flow
Isolated
population
diverges
Hybrid
zone
Hybrid
individual

106. Figure 24.14-4
Gene flow
Population
Barrier to
gene flow
Isolated
population
diverges
Hybrid
zone
Hybrid
individual
Possible
outcomes:
Reinforcement
OR
OR
Fusion
Stability

107. Reinforcement: Strengthening Reproductive
Barriers
• The reinforcement of barriers occurs when
hybrids are less fit than the parent species
• Over time, the rate of hybridization decreases
• Where reinforcement occurs, reproductive barriers
should be stronger for sympatric than allopatric
species
– For example, in populations of flycatchers, males
are more similar in allopatric populations than
sympatric populations
© 2011 Pearson Education, Inc.

108. Figure 24.15
Females choosing between
these males:
Females choosing between
these males:
Sympatric pied male
Sympatric collared male
Allopatric pied male
Allopatric collared male
(none)
Female mate choice Female mate choice
Own
species
Own
species
Other
species
Other
species
Numberoffemales
28
24
20
16
12
8
4
0

109. Fusion: Weakening Reproductive Barriers
• If hybrids are as fit as parents, there can be
substantial gene flow between species
• If gene flow is great enough, the parent
species can fuse into a single species
• For example, researchers think that pollution
in Lake Victoria has reduced the ability of
female cichlids to distinguish males of
different species
• This might be causing the fusion of many
species
© 2011 Pearson Education, Inc.

110. Figure 24.16
Pundamilia nyererei Pundamilia pundamilia
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water

111. Figure 24.16a
Pundamilia nyererei

112. Figure 24.16b
Pundamilia pundamilia

113. Figure 24.16c
Pundamilia “turbid water,” hybrid offspring from a
location with turbid water

114. Stability: Continued Formation of Hybrid
Individuals
• Extensive gene flow from outside the hybrid zone
can overwhelm selection for increased
reproductive isolation inside the hybrid zone
© 2011 Pearson Education, Inc.

115. Concept 24.4: Speciation can occur rapidly
or slowly and can result from changes in
few or many genes
• Many questions remain concerning how long it
takes for new species to form, or how many genes
need to differ between species
© 2011 Pearson Education, Inc.

116. The Time Course of Speciation
• Broad patterns in speciation can be studied
using the fossil record, morphological data, or
molecular data
© 2011 Pearson Education, Inc.

117. Patterns in the Fossil Record
• The fossil record includes examples of species
that appear suddenly, persist essentially
unchanged for some time, and then apparently
disappear
• Niles Eldredge and Stephen Jay Gould coined the
term punctuated equilibria to describe periods of
apparent stasis punctuated by sudden change
• The punctuated equilibrium model contrasts with a
model of gradual change in a species’ existence
© 2011 Pearson Education, Inc.

118. Figure 24.17
a) Punctuated
pattern
Time
b) Gradual
pattern

119. Speciation Rates
• The punctuated pattern in the fossil record and
evidence from lab studies suggest that speciation
can be rapid
– For example, the sunflower Helianthus anomalus
originated from the hybridization of two other
sunflower species
© 2011 Pearson Education, Inc.

120. Figure 24.18

121. Figure 24.19
H. annuus
gamete
H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
EXPERIMENT
RESULTS
Chromosome 1
H. anomalus
Chromosome 2
H. anomalus
Experimental hybrid
Experimental hybrid

122. Figure 24.19a
H. annuus
gamete
H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
EXPERIMENT

123. Figure 24.19b
RESULTS
Chromosome 1
H. anomalus
Chromosome 2
H. anomalus
Experimental hybrid
Experimental hybrid

124. • The interval between speciation events can range
from 4,000 years (some cichlids) to 40 million
years (some beetles), with an average of 6.5
million years
© 2011 Pearson Education, Inc.

125. Studying the Genetics of Speciation
• A fundamental question of evolutionary biology
persists: How many genes change when a new
species forms?
• Depending on the species in question, speciation
might require the change of only a single allele or
many alleles
– For example, in Japanese Euhadra snails, the
direction of shell spiral affects mating and is
controlled by a single gene
© 2011 Pearson Education, Inc.

126. • In monkey flowers (Mimulus), two loci affect flower
color, which influences pollinator preference
• Pollination that is dominated by either
hummingbirds or bees can lead to reproductive
isolation of the flowers
• In other species, speciation can be influenced by
larger numbers of genes and gene interactions
© 2011 Pearson Education, Inc.

127. Typical
Mimulus
lewisii
(a)
Typical
Mimulus
cardinalis
(c)
M. lewisii with an
M. cardinalis flower-color
allele
(b)
M. cardinalis with an
M. lewisii flower-color
allele
(d)
Figure 24.20

128. Figure 24.20a
Typical Mimulus lewisii(a)

129. Figure 24.20b
M. lewisii with an
M. cardinalis flower-color
allele
(b)

130. Figure 24.20c
Typical Mimulus cardinalis(c)

131. Figure 24.20d
M. cardinalis with an
M. lewisii flower-color
allele
(d)

132. From Speciation to Macroevolution
• Macroevolution is the cumulative effect of many
speciation and extinction events
© 2011 Pearson Education, Inc.

133. Figure 24.UN01
Cell
division
error
2n = 6 Tetraploid cell
4n = 12
2n
2n New species
(4n)Gametes produced
by tetraploids

134. Figure 24.UN02
Original population
Allopatric speciation Sympatric speciation

135. Figure 24.UN03
Ancestral species:
Product:
Triticum
monococcum
(2n = 14)
Wild
Triticum
(2n = 14)
Wild
T. tauschii
(2n = 14)
T. aestivum
(bread wheat)
(2n = 42)

136. Figure 24.UN04