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Chapter 14
The Origin of Species
PowerPoint Lectures
Campbell Biology: Concepts & Connections, Eighth Edition
REECE • TAYLOR • SIMON • DICKEY • HOGAN
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Lecture by Edward J. Zalisko
Figure 14.0-2
Chapter 14: Big Ideas
Defining Species
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Mechanisms
of Speciation
DEFINING SPECIES
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14.1 The origin of species is the source of
biological diversity
•  Darwin was eager to explore landforms newly
emerged from the sea when he came to the
Galápagos Islands.
•  He noted that these volcanic islands, despite their
geologic youth, were teeming with plants and
animals found nowhere else in the world.
•  He realized that these species, like the islands,
were relatively new.
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14.1 The origin of species is the source of
biological diversity
•  Microevolution is the change in the gene pool of a
population from one generation to the next.
•  Speciation is the process by which one species
splits into two or more species.
•  Each time speciation occurs, the diversity of life
increases.
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Figure 14.1
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14.1 The origin of species is the source of
biological diversity
•  Over the course of 3.5 billion years,
•  an ancestral species first gave rise to two or more
different species,
•  which then branched to new lineages,
•  which branched again,
•  until we arrive at the millions of species that live, or
once lived, on Earth.
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14.2 There are several ways to define a
species
•  The word species is from the Latin for “kind” or
“appearance.”
•  Although the basic idea of species as distinct lifeforms seems intuitive, devising a more formal
definition is not easy and raises questions.
•  In many cases, the differences between two
species are obvious. In other cases, the
differences between two species are not so
obvious.
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Figure 14.2a-0
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14.2 There are several ways to define a
species
•  How similar are members of the same species?
•  Whereas the individuals of many species exhibit
fairly limited variation in physical appearance,
certain other species—our own, for example—seem
extremely varied.
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Figure 14.2b
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14.2 There are several ways to define a
species
•  The biological species concept defines a
species as a group of populations whose members
have the potential to interbreed in nature and
produce fertile offspring (offspring that themselves
can reproduce).
•  Thus, members of a biological species are united
by being reproductively compatible, at least
potentially.
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14.2 There are several ways to define a
species
•  Reproductive isolation
•  prevents genetic exchange (gene flow) and
•  maintains a boundary between species.
•  But there are some pairs of clearly distinct species
that do occasionally interbreed.
•  The resulting offspring are called hybrids.
•  An example is the grizzly bear (Ursus arctos) and
the polar bear (Ursus maritimus), whose hybrid
offspring have been called “grolar bears.”
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Figure 14.2c-0
Grizzly bear
Polar bear
Hybrid “grolar” bear
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14.2 There are several ways to define a
species
•  There are other instances in which applying the
biological species concept is problematic.
•  There is no way to determine whether organisms
that are now known only through fossils were once
able to interbreed.
•  Reproductive isolation does not apply to
prokaryotes or other organisms that reproduce only
asexually.
•  Therefore, alternate species concepts can be
useful.
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14.2 There are several ways to define a
species
•  The morphological species concept
•  classifies organisms based on observable physical
traits and
•  can be applied to asexual organisms and fossils.
•  However, there is some subjectivity in deciding
which traits to use.
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14.2 There are several ways to define a
species
•  The ecological species concept
•  defines a species by its ecological niche and
•  focuses on unique adaptations to particular roles in
a biological community.
•  For example, two species may be similar in
appearance but distinguishable based on what
they eat or the depth of water in which they are
usually found.
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14.2 There are several ways to define a
species
•  The phylogenetic species concept defines a species
as the smallest group of individuals that share a
common ancestor and thus form one branch of the tree
of life.
•  Biologists trace the phylogenetic history of a species by
comparing its
•  morphology,
•  DNA sequences, or
•  biochemical pathways.
•  However, agreeing on the amount of difference required
to establish separate species remains a challenge.
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14.3 VISUALIZING THE CONCEPT:
Reproductive barriers keep species separate
•  Reproductive barriers
•  serve to isolate the gene pools of species and
•  prevent interbreeding.
•  Depending on whether they function before or after
zygotes form, reproductive barriers are categorized
as
•  prezygotic or
•  postzygotic.
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14.3 VISUALIZING THE CONCEPT:
Reproductive barriers keep species separate
•  Five types of prezygotic barriers prevent mating
or fertilization between species.
1.  In habitat isolation, there is a lack of opportunity
for mates to encounter each other.
2.  In temporal isolation, there is breeding at different
times or seasons.
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Figure 14.3-0
PREZYGOTIC BARRIERS
Habitat isolation
(different habitats)
Temporal isolation
(breeding at different times)
Mechanical isolation
(incompatible reproductive parts)
Behavioral isolation
(different courtship rituals)
Gametic isolation
(incompatible gametes)
POSTZYGOTIC BARRIERS
Reduced hybrid vitality
(short-lived hybrids)
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Reduced hybrid fertility
(sterile hybrids)
Hybrid breakdown
(fertile hybrids with
sterile offspring)
Figure 14.3-1
Habitat isolation
(lack of opportunities to encounter each other)
The garter snake Thamnophis
atratus lives mainly in water.
The garter snake
Thamnophis sirtalis
lives on land.
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Figure 14.3-2
Temporal isolation
(breeding at different times or seasons)
The eastern spotted skunk
(Spilogale putorius) breeds in
late winter.
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The western spotted skunk
(Spilogale gracilis) breeds in
the fall.
14.3 VISUALIZING THE CONCEPT:
Reproductive barriers keep species separate
3.  In behavioral isolation, there is failure to send or
receive appropriate signals.
4.  In mechanical isolation, there is physical
incompatibility of reproductive parts.
5.  In gametic isolation, there is molecular
incompatibility of eggs and sperm or pollen and
stigma.
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Video: Blue-Footed Boobies Courtship Ritual
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Video: Albatross Courtship Ritual
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Video: Giraffe Courtship Ritual
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Figure 14.3-3
Behavioral isolation
(different courtship rituals)
The blue-footed booby
(Sula nebouxii) performs an
elaborate courtship dance.
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The masked booby
(Sula dactylatra) performs
a different courtship ritual.
Figure 14.3-4
Mechanical isolation
(physical incompatibility of reproductive parts)
Heliconia latispatha is pollinated
by hummingbirds with short,
straight bills.
Heliconia pogonantha is
pollinated by hummingbirds
with long, curved bills.
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Figure 14.3-5
Gametic isolation
(molecular incompatibility of eggs and sperm
or pollen and stigma)
Purple sea urchin
(Strongylocentrotus
purpuratus)
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Red sea urchin
(Strongylocentrotus
franciscanus)
14.3 VISUALIZING THE CONCEPT:
Reproductive barriers keep species separate
•  Three types of postzygotic barriers operate after
hybrid zygotes have formed.
1.  In reduced hybrid viability, interaction of parental
genes impairs the hybrid’s development or
survival.
2.  In reduced hybrid fertility, hybrids are vigorous but
cannot produce viable offspring.
3.  In hybrid breakdown, hybrids are viable and
fertile, but their offspring are feeble or sterile.
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Figure 14.3-6
Reduced hybrid viability
(hybrid development or survival impaired
by interaction of parental genes)
Some salamander species can hybridize,
but their offspring do not develop fully or
are frail and will not survive long enough
to reproduce.
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Figure 14.3-7
Reduced hybrid fertility
(vigorous hybrids that cannot
produce viable offspring)
A mule is the sterile hybrid
offspring of a horse and a donkey.
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Figure 14.3-8
Hybrid breakdown
(viable and fertile hybrids with feeble
or sterile offspring)
The rice hybrids on the left and right
are fertile, but plants of the next
generation (middle) are sterile.
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MECHANISMS OF SPECIATION
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14.4 In allopatric speciation, geographic
isolation leads to speciation
•  A key event in the origin of a new species is the
separation of a population from other populations
of the same species.
•  With its gene pool isolated, the splinter population
can follow its own evolutionary course.
•  Changes in allele frequencies caused by natural
selection, genetic drift, and mutation will not be
diluted by alleles entering from other populations
(gene flow).
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14.4 In allopatric speciation, geographic
isolation leads to speciation
•  In allopatric speciation, the initial block to gene
flow may come from a geographic barrier that
isolates a population.
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14.4 In allopatric speciation, geographic
isolation leads to speciation
•  Several geologic processes can isolate
populations.
•  A mountain range may emerge and gradually split a
population of organisms that can inhabit only
lowlands.
•  A large lake may subside until there are several
smaller lakes, isolating certain fish populations.
•  Continents themselves can split and move apart.
•  Allopatric speciation can also occur when
individuals colonize a remote area and become
geographically isolated from the parent population.
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14.4 In allopatric speciation, geographic
isolation leads to speciation
•  How large must a geographic barrier be to keep
allopatric populations apart?
•  The answer depends on the ability of the organisms
to move.
•  Birds, mountain lions, and coyotes can easily cross
mountain ranges.
•  In contrast, small rodents may find a canyon or a
wide river a formidable barrier. The Grand Canyon
and Colorado River separate two species of
antelope squirrels.
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Figure 14.4a-0
North rim
South rim
A. harrisii
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A. leucurus
14.4 In allopatric speciation, geographic
isolation leads to speciation
•  Thirty species of snapping shrimp in the genus
Alpheus live off the Isthmus of Panama, the land
bridge that connects South and North America.
•  Morphological and genetic data group these shrimp into
15 pairs of species, with the members of each pair
being each other’s closest relative.
•  In each case, one member of the pair lives on the
Atlantic side of the isthmus, while the other lives on the
Pacific side.
•  This strongly suggests that geographic separation of the
ancestral species of these snapping shrimp led to
allopatric speciation.
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Figure 14.4b
A. formosus
A. nuttingi
ATLANTIC OCEAN
Isthmus of Panama
PACIFIC OCEAN
A. panamensis
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A. millsae
14.5 Reproductive barriers can evolve as
populations diverge
•  How do reproductive barriers arise?
•  The environment of an isolated population may
include
•  different food sources,
•  different types of pollinators, and
•  different predators.
•  As a result of natural selection acting on
preexisting variations (or as a result of genetic drift
or mutation), a population’s traits may change in
ways that also establish reproductive barriers.
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14.5 Reproductive barriers can evolve as
populations diverge
•  Researchers have successfully documented the
evolution of reproductive isolation with laboratory
experiments.
•  These studies have included
•  laboratory studies of fruit flies and
•  field studies of monkey flowers and their pollinators.
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Figure 14.5a
Initial sample
of fruit flies
Starch medium
Maltose medium
22
9
8
20
Results
Number of matings
in experimental groups
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Female
Population Population
#2
#1
Pop#2 Pop#1
Female
Starch
Maltose
Male
Maltose Starch
Male
Mating experiments
18
15
12
15
Number of matings
In starch control groups
Figure 14.5b-0
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Pollinator choice in
typical monkey flowers
Pollinator choice after
color allele transfer
Typical M. lewisii
(pink)
M. lewisii with
red-color allele
Typical M. cardinalis
(red)
M. cardinalis with
pink-color allele
14.6 Sympatric speciation takes place
without geographic isolation
•  Sympatric speciation occurs when a new species
arises within the same geographic area as its
parent species.
•  How can reproductive isolation develop when
members of sympatric populations remain in
contact with each other?
•  Gene flow between populations may be reduced by
•  polyploidy,
•  habitat differentiation, or
•  sexual selection.
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14.6 Sympatric speciation takes place
without geographic isolation
•  Many plant species have originated from sympatric
speciation that occurs when accidents during cell
division result in extra sets of chromosomes.
•  New species formed in this way are polyploid, in
that their cells have more than two complete sets
of chromosomes.
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14.6 Sympatric speciation takes place
without geographic isolation
•  Sympatric speciation can result from polyploidy
•  within a species (by self-fertilization) or
•  between two species (by hybridization).
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Figure 14.6a-3
1
2
Parent species
2n = 6
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Tetraploid
cells
4n = 12
3
Selffertilization
Diploid
gametes
2n = 6
Viable, fertile
tetraploid
species
4n = 12
Figure 14.6b-3
Chromosomes
cannot pair
Species A
2n = 4
Species B
2n = 6
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Gamete
n=2
Gamete
n=3
3
1
Sterile hybrid
n=5
Can reproduce
asexually
2
Viable, fertile
hybrid species
2n = 10
14.7 EVOLUTION CONNECTION: The origin of
most plant species can be traced to polyploid
speciation
•  Plant biologists estimate that 80% of all living plant
species are descendants of ancestors that formed
by polyploid speciation.
•  Hybridization between two species accounts for
most of these species, perhaps because of the
adaptive advantage of the diverse genes a hybrid
inherits from different parental species.
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14.7 EVOLUTION CONNECTION: The origin of
most plant species can be traced to polyploid
speciation
•  Polyploid plants include
•  cotton,
•  oats,
•  potatoes,
•  bananas,
•  peanuts,
•  barley,
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•  plums,
•  apples,
•  sugarcane,
•  coffee, and
•  wheat.
14.7 EVOLUTION CONNECTION: The origin of
most plant species can be traced to polyploid
speciation
•  Wheat
•  has been domesticated for at least 10,000 years
and
•  is the most widely cultivated plant in the world.
•  Bread wheat, Triticum aestivum, is
•  a polyploid with 42 chromosomes and
•  the result of hybridization and polyploidy.
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Figure 14.7-0
AA
BB
Wild Triticum
(14 chromosomes)
Domesticated
Triticum monococcum
(14 chromosomes)
1
Hybridization
AB
Sterile hybrid
(14 chromosomes)
Cell division error
and self-fertilization
2
DD
AABB
T. turgidum
Emmer wheat
(28 chromosomes)
Wild
T. tauschii
(14 chromosomes)
3
Hybridization
ABD
Sterile hybrid
(21 chromosomes)
4
Cell division error
and self-fertilization
AABBDD
T. aestivum
Bread wheat
(42 chromosomes)
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14.8 Isolated islands are often showcases of
speciation
•  Isolated island chains are often inhabited by
unique collections of species.
•  Islands that have physically diverse habitats and
that are far enough apart to permit populations to
evolve in isolation but close enough to allow
occasional dispersions to occur are often the sites
of multiple speciation events.
•  The evolution of many diverse species from a
common ancestor is known as adaptive radiation.
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14.8 Isolated islands are often showcases of
speciation
•  The Galápagos Archipelago
•  is located about 900 km (560 miles) west of
Ecuador,
•  is one of the world’s great showcases of adaptive
radiation,
•  was formed naked from underwater volcanoes from
5 million to 1 million years ago,
•  was colonized gradually from other islands and the
South America mainland, and
•  has many species of plants and animals found
nowhere else in the world.
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14.8 Isolated islands are often showcases of
speciation
•  The Galápagos Islands currently have 14 species
of closely related finches, called Darwin’s finches,
because Darwin collected them during his aroundthe-world voyage on the Beagle.
•  These birds
•  share many finchlike traits,
•  differ in their feeding habits and their beaks,
specialized for what they eat, and
•  arose through adaptive radiation.
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Figure 14.8-0
Cactus-seed-eater (cactus finch)
Tool-using insect-eater
(woodpecker finch)
Seed-eater (large ground finch)
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  We can see speciation occurring.
•  The species living today represent a snapshot, a
brief instant in this vast span of time.
•  The environment continues to change, sometimes
rapidly due to human impact, and natural selection
continues to act on affected populations.
•  Researchers have documented at least two dozen
cases in which populations are diverging as they
exploit different food resources or breed in different
habitats.
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  Sexual selection is a form of natural selection in
which individuals with certain traits are more likely
to obtain mates.
•  In addition to the bowerbirds already discussed,
biologists have identified several other animal
populations that are diverging as a result of
differences in how males attract females or how
females choose mates.
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  Biologists can also test hypotheses about the process
of speciation by studying species that arose recently.
•  Cichlids are a family of fishes that live in tropical lakes
and rivers.
•  They come in all colors of the rainbow.
•  They are renowned for the spectacular adaptive
radiations that stocked the large lakes of East Africa
with more than a thousand species of cichlids in less
than 100,000 years.
•  In the largest of these lakes, Lake Victoria, roughly 500
species evolved in about 15,000 years.
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Figure 14.9a
Uganda
Kenya
Lake
Victoria
Tanzania
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Indian
Ocean
14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  In Lake Victoria, there are pairs of closely related
cichlid species that differ in color but nothing else.
•  Breeding males of Pundamilia nyererei have a
bright red back and dorsal fin.
•  Breeding males of Pundamilia pundamilia males
are metallic blue-gray.
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Figure 14.9b
Pundamilia nyererei
Pundamilia pundamilia
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  Pundamilia females prefer brightly colored males.
•  Mate-choice experiments performed in the laboratory
showed that
•  P. nyererei females prefer red males over blue males,
•  P. pundamilia females prefer blue males over red males,
•  the vision of P. nyererei females is more sensitive to red
light than blue light, and
•  the vision of P. pundamilia females is more sensitive to
blue light than red light.
•  Researchers also demonstrated that this color
sensitivity is heritable.
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  As light travels through water, suspended particles
selectively absorb and scatter the shorter (blue)
wavelengths, so light becomes increasingly red
with increasing depth.
•  Thus, in deeper waters, P. nyererei males are
pleasingly apparent to females with red-sensitive
vision but virtually invisible to P. pundamilia
females.
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
•  When biologists sampled cichlid populations in
Lake Victoria, they found that
•  P. nyererei breeds in deep water, while
•  P. pundamilia inhabits shallower habitats where the
blue males shine brightly.
•  As a consequence of their mating behavior, the two
species encounter different environments that may
result in further divergence.
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14.10 Hybrid zones provide opportunities to
study reproductive isolation
•  What happens when separated populations of
closely related species come back into contact with
each other?
•  Biologists try to answer such questions by studying
hybrid zones, regions in which members of
different species meet and mate to produce at
least some hybrid offspring.
•  Figure 14.10A illustrates the formation of a hybrid
zone, starting with the ancestral species.
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Figure 14.10a
Newly formed
species
Three
populations
of a species
3
Hybrid
zone
2
1
4
Gene flow
Population
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Barrier to
gene flow
Gene
flow
Hybrid
individual
14.10 Hybrid zones provide opportunities to
study reproductive isolation
•  Reinforcement
•  When hybrid offspring are less fit than members of
both parent species, we might expect
•  natural selection to strengthen, or reinforce,
reproductive barriers, thus reducing the formation of
unfit hybrids, and
•  that barriers between species should be stronger
where the species overlap (that is, where the
species are sympatric).
•  The closely related collared flycatcher and pied
flycatcher are an example of reinforcement.
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Figure 14.10b-0
Allopatric
populations
Sympatric
populations
Pied flycatcher
from allopatric
population
Pied flycatcher
from sympatric
population
Male
collared
flycatcher
Male
pied
flycatcher
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14.10 Hybrid zones provide opportunities to
study reproductive isolation
•  Fusion
•  What happens when the reproductive barriers
between species are not strong and the species
come into contact in a hybrid zone?
•  So much gene flow may occur that the speciation
process reverses, causing the two hybridizing
species to fuse into one.
•  Such a situation has been occurring among the
cichlid species in Lake Victoria.
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14.10 Hybrid zones provide opportunities to
study reproductive isolation
•  Pollution caused by development along the shores
of Lake Victoria has turned the water murky.
•  What happens when P. nyererei or P. pundamilia
females can’t tell red males from blue males?
•  The behavioral barrier crumbles.
•  Many viable hybrid offspring are produced by
interbreeding.
•  The once isolated gene pools of the parent species
are combining, with two species fusing into a single
hybrid species.
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Figure 14.10c
Hybrid: Pundamilia “turbid water”
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14.11 Speciation can occur rapidly or slowly
•  There are two models for the tempo of speciation.
1.  The punctuated equilibria model draws on the
fossil record, where species change most as they
arise from an ancestral species and then change
relatively little for the rest of their existence.
2.  Other species appear to have evolved more
gradually.
•  The time interval between speciation events varies
from a few thousand years to tens of millions of
years.
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Animation: Macroevolution
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Figure 14.11
Punctuated pattern
Gradual pattern
Time
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You should now be able to
1.  Distinguish between microevolution and
speciation.
2.  Compare the definitions, advantages, and
disadvantages of the different species concepts.
3.  Describe five types of prezygotic barriers and
three types of postzygotic barriers that prevent
populations of closely related species from
interbreeding.
4.  Explain how geologic processes can fragment
populations and lead to speciation.
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You should now be able to
5.  Explain how reproductive barriers might evolve in
isolated populations of organisms.
6.  Explain how sympatric speciation can occur,
noting examples in plants and animals.
7.  Explain why polyploidy is important to modern
agriculture.
8.  Explain how modern wheat evolved.
9.  Describe the circumstances that led to the
adaptive radiation of the Galápagos finches.
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You should now be able to
10.  Explain how new species of fish have evolved
in Lake Victoria.
11.  Explain how hybrid zones are useful in the
study of reproductive isolation.
12.  Compare the gradual model and the
punctuated equilibrium model of evolution.
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