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Chapter 14
The Origin of Species
PowerPoint Lectures
Campbell Biology: Concepts & Connections, Eighth Edition
REECE • TAYLOR • SIMON • DICKEY • HOGAN
© 2015 Pearson Education, Inc.
Lecture by Edward J. Zalisko
DEFINING SPECIES
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I can…
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.
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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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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.
• Thus, members of a biological species are united
by being reproductively compatible.
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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.
• Hybrids: clearly distinct species that
do occasionally interbreed.
• An example is the grizzly bear
and the polar bear, whose hybrid
offspring have been called “grolar
bears.”
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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.
• The ecological species concept
• defines a species by its ecological niche and focuses on
unique adaptations to particular roles in a biological
community.
• 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.
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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.
• Reproductive barriers are categorized as
• Prezygotic: before zygotes form
• Postzygotic: after zygotes form
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14.3 Reproductive barriers keep species
separate
• Five types of prezygotic barriers prevent mating or fertilization
between species.
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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 Reproductive barriers keep species
separate
Blue footed booby courtship
ritual:
http://www.arkive.org/bluefooted-booby/sulanebouxii/video-09a.html
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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.
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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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I can…
1. Explain how geologic processes can fragment
populations and lead to speciation.
2. Explain how reproductive barriers might evolve
in isolated populations of organisms.
3. Explain how sympatric speciation can occur.
4. Describe the circumstances that led to the
adaptive radiation of the Galápagos finches.
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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.
• How large must a geographic barrier be to keep
allopatric populations apart?
• depends on the ability of the organisms to move
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14.5 Reproductive barriers can evolve as
populations diverge
• How do reproductive barriers arise?
• 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.
• http://www.hhmi.org/biointeractive/anole-lizardsexample-speciation (3 min)
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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 (usually plants),
• habitat differentiation or sexual selection (usually
animals) .
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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 selffertilization)
• between two
species (by
hybridization).
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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 The origin of most plant species can be
traced to polyploid speciation
• Polyploid plants include
•
•
•
•
•
•
•
•
•
•
•
cotton,
oats,
potatoes,
bananas,
peanuts,
barley,
plums,
apples,
sugarcane,
coffee, and
wheat.
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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 Islands
currently have 14 species of
closely related finches.
• These birds
• differ in their feeding
habits and their beaks,
specialized for what they
eat, and arose through
adaptive radiation.
http://www.hhmi.org/biointeracti
ve/origin-species-beak-finch
(16 min)
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I can…
1. Explain how new species of fish have evolved in
Lake Victoria.
2. Explain how hybrid zones are useful in the study
of reproductive isolation.
3. Compare the gradual model and the punctuated
equilibrium model of evolution.
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14.9 SCIENTIFIC THINKING: Lake Victoria is a
living laboratory for studying speciation
• Biologists are still studying the
process of speciation.
• Cichlid fish populations
• They come in all colors of the
rainbow.
• Live in 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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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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14.9 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 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.
• 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.
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14.10 Hybrid zones provide opportunities to study
reproductive isolation
• Species may interbreed in a hybrid zone.
• There are 3 possible hybrid zone outcomes
• Reinforcement: when reproductive barriers are
strengthened and keep species separate.
• Fusion: when reproductive barriers are weakened or
eliminated and speciation is reversed.
• Stability: when a few hybrids continue to be produced.
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• When hybrid offspring are less
fit than members of both parent
species,
• natural selection to
strengthen, or reinforce,
reproductive barriers
• barriers between species
should be stronger where
the species overlap
(sympatric).
• The closely related collared
flycatcher and pied flycatcher
are an example of
reinforcement.
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14.10 Hybrid zones provide opportunities to
study reproductive isolation
• Fusion
• 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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14.10 Hybrid zones provide opportunities to
study reproductive isolation
• Stability
• Many hybrid zones are fairly stable and hybrids
continue to be produced.
• Example: the islands inhabited by two finch species
occasionally interbreed.
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Speciation of California Salamanders and
Hybrid Zones
https://www.youtube.com/watch?v=aDIQFQOCGaI
(3.5 min)
Is this an example of reinforcement, fusion, or
stability?
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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: long periods of little
apparent morphological change (equilibria)
interrupted (punctuated) by relatively brief periods
of sudden change.
2. Other species appear to have evolved more
gradually.
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Figure 14.11
Punctuated pattern
Gradual pattern
Time
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Crash Course: Speciation
• https://www.youtube.com/watch?v=2oKlKmrbLoU
• 10:25 min
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Figure 14.UN05
Zygote
Gametes Prezygotic barriers
• Habitat isolation
• Temporal isolation
• Behavioral isolation
• Mechanical isolation
• Gametic isolation
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Postzygotic barriers
• Reduced hybrid
viability
• Reduced hybrid
fertility
• Hybrid breakdown
Viable,
fertile
offspring
Figure 14.UN06
Original population
a.
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b.
Figure 14.UN07
Species
may interbreed
in a
a.
outcome may be
b.
c.
when
d.
when
when
are
a few
hybrids
continue to
be produced
reproductive
barriers
are
e.
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f.
keeps
and
species
separate
speciation is
reversed