© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
Chapter 14 The Origin of Species
Many species of cormorants around the world can
fly.
Cormorants on the Galápagos Islands cannot fly.
How did these flightless cormorants get to the
Galápagos Islands?
Why are these flightless cormorants found
nowhere else in the world?
Introduction
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Figure 14.0_1
Defining Species Mechanisms
of Speciation
Chapter 14: Big Ideas
Figure 14.0_2
An ancestral cormorant species is thought to have
flown from the Americas to the Galápagos Islands
more than 3 million years ago.
Terrestrial mammals could not make the trip over
the wide distance, and no predatory mammals
naturally occur on these islands today.
Without predators, the environment of these
cormorants favored birds with smaller wings,
perhaps channeling resources to the production of
offspring.
Introduction
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DEFINING SPECIES
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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.
– Every time speciation occurs, the diversity of life increases.
– The many millions of species on Earth have all arisen from an ancestral life form that lived around 3.5 billion years ago.
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Figure 14.1
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 life-forms seems intuitive, devising a more formal definition is not easy and raises questions.
– How similar are members of the same species?
– What keeps one species distinct from others?
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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.
– Therefore, members of a species are similar because they reproduce with each other.
14.2 There are several ways to define a species
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Reproductive isolation
– prevents members of different species from mating with each other,
– prevents gene flow between species, and
– maintains separate species.
– Therefore, species are distinct from each other because they do not share the same gene pool.
14.2 There are several ways to define a species
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Figure 14.2A
Figure 14.2A_1
Figure 14.2A_2
Figure 14.2B
The biological species concept can be problematic.
– Some pairs of clearly distinct species occasionally interbreed and produce hybrids.
– For example, grizzly bears and polar bears may interbreed and produce hybrids called grolar bears.
– Melting sea ice may bring these two bear species together more frequently and produce more hybrids in the wild.
– Reproductive isolation cannot usually be determined for extinct organisms known only from fossils.
– Reproductive isolation does not apply to prokaryotes or other organisms that reproduce only asexually.
– Therefore, alternate species concepts can be useful.
14.2 There are several ways to define a species
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Figure 14.2C
Grizzly bear Polar bear
Hybrid “grolar” bear
Figure 14.2C_1
Grizzly bear
Figure 14.2C_2
Polar bear
Figure 14.2C_3
Hybrid “grolar” bear
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.
14.2 There are several ways to define a species
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The ecological species concept
– defines a species by its ecological role or 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
– where they live.
14.2 There are several ways to define a species
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The phylogenetic species concept
– defines a species as the smallest group of individuals that
shares a common ancestor and thus
– forms one branch of the tree of life.
– Biologists trace the phylogenetic history of a species by
comparing its
– morphology or
– DNA.
– However, defining the amount of difference required to
distinguish separate species is a problem.
14.2 There are several ways to define a species
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14.3 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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Figure 14.3A
Individuals of different species
Prezygotic Barriers
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Fertilization
Postzygotic Barriers
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Viable, fertile offspring
Five types of prezygotic barriers prevent mating or
fertilization between species.
1. In habitat isolation, two species live in the same general
area but not in the same kind of place.
2. In temporal isolation, two species breed at different times
(seasons, times of day, years).
14.3 Reproductive barriers keep species separate
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Video: Giraffe Courtship Ritual
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Figure 14.3B
Figure 14.3B_1
Figure 14.3B_2
Figure 14.3C
Figure 14.3C_1
Figure 14.3C_2
Prezygotic Barriers, continued
3. In behavioral isolation, there is little or no mate
recognition between females and males of different
species.
4. In mechanical isolation, female and male sex organs are
not compatible.
5. In gametic isolation, female and male gametes are not
compatible.
14.3 Reproductive barriers keep species separate
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Figure 14.3D
Figure 14.3E
Figure 14.3F
Three types of postzygotic barriers operate after
hybrid zygotes have formed.
1. In reduced hybrid viability, most hybrid offspring do not
survive.
2. In reduced hybrid fertility, hybrid offspring are vigorous
but sterile.
3. In hybrid breakdown,
– the first-generation hybrids are viable and fertile but
– the offspring of the hybrids are feeble or sterile.
14.3 Reproductive barriers keep species separate
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Figure 14.3G
Horse Donkey
Mule
Figure 14.3G_1
Horse
Figure 14.3G_2
Donkey
Figure 14.3G_3
Mule
MECHANISMS
OF SPECIATION
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14.4 In allopatric speciation, geographic isolation leads to speciation
In allopatric speciation, populations of the same
species are geographically separated, isolating their
gene pools.
Isolated populations will no longer share changes in
allele frequencies caused by
– natural selection,
– genetic drift, and/or
– mutation.
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Gene flow between populations is initially prevented
by a geographic barrier. For example
– the Grand Canyon and Colorado River separate two
species of antelope squirrels, and
– the Isthmus of Panama separates 15 pairs of snapping
shrimp.
14.4 In allopatric speciation, geographic isolation leads to speciation
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Figure 14.4A
South rim
A. harrisii
North rim
A. leucurus
Figure 14.4A_1
A. harrisii
Figure 14.4A_2
A. leucurus
Figure 14.4B
Isthmus of Panama
A. millsae
A. nuttingi A. formosus
A. panamensis
ATLANTIC OCEAN
PACIFIC OCEAN
14.5 Reproductive barriers can evolve as populations diverge
How do reproductive barriers arise?
Experiments have demonstrated that reproductive
barriers can evolve as a by-product of changes in
populations as they adapt to different environments.
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
Starch medium Maltose medium
Initial sample
of fruit flies
Mating experiments
Female Female
Results Population
#1
Population
#2 Starch Maltose
Ma
le
Ma
lto
se
S
tarc
h
22
8 20
9 18 15
15 12 Ma
le
Po
p#
2 P
op
#1
Number of matings
in experimental groups
Number of matings
in starch control groups
Figure 14.5B
Pollinator choice in
typical monkey flowers
Typical M. lewisii
(pink)
M. lewisii with
red-color allele
Typical M. cardinalis
(red) M. cardinalis with
pink-color allele
Pollinator choice after
color allele transfer
Figure 14.5B_1
Typical M. lewisii
(pink)
Figure 14.5B_2
M. lewisii with
red-color allele
Figure 14.5B_3
Typical M. cardinalis
(red)
Figure 14.5B_4
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 a 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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Many plant species have evolved by polyploidy in
which cells have more than two complete sets of
chromosomes.
Sympatric speciation can result from polyploidy
– within a species (by self-fertilization) or
– between two species (by hybridization).
14.6 Sympatric speciation takes place without geographic isolation
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Figure 14.6A_s1
Parent species 2n = 6
Tetraploid cells
4n = 12
1
Figure 14.6A_s2
Parent species 2n = 6
Tetraploid cells
4n = 12
1
Diploid gametes 2n = 6
2
Figure 14.6A_s3
Parent species 2n = 6
Tetraploid cells
4n = 12
Diploid gametes 2n = 6
Viable, fertile tetraploid species 4n = 12
Self- fertilization
3 1
2
Figure 14.6B_s1
Species A 2n = 4
Gamete n = 2
Gamete n = 3
Species B 2n = 6
Figure 14.6B_s2
Species A 2n = 4
Gamete n = 2
Gamete n = 3
Species B 2n = 6
Chromosomes cannot pair
Can reproduce asexually
Sterile hybrid n = 5
1
2
Figure 14.6B_s3
Species A 2n = 4
Gamete n = 2
Gamete n = 3
Species B 2n = 6
Chromosomes cannot pair
Can reproduce asexually
Sterile hybrid n = 5
1
2
Viable, fertile hybrid species
2n = 10
3
14.7 EVOLUTION CONNECTION: Most plant species trace their origin 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.
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14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
Polyploid plants include
– cotton,
– oats,
– potatoes,
– bananas,
– peanuts,
– barley,
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– plums,
– apples,
– sugarcane,
– coffee, and
– bread wheat.
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.
14.7 EVOLUTION CONNECTION: Most plant species trace their origin to polyploid speciation
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Figure 14.7_3
Figure 14.7
Domesticated
Triticum monococcum
(14 chromosomes)
AA
DD AABB
Wild Triticum
(14 chromo-
somes)
Hybridization
AB
Sterile hybrid (14 chromosomes)
1
2
3
4
Cell division error and self-fertilization
Hybridization
Wild T. tauschii (14 chromosomes)
T. turgidum Emmer wheat (28 chromosomes)
ABD
Sterile hybrid (21 chromosomes)
Cell division error
and self-fertilization
AABBDD
T. aestivum Bread wheat (42 chromosomes)
BB
Figure 14.7_1
Domesticated
Triticum monococcum
(14 chromosomes)
AA
DD AABB
Hybridization
AB
Sterile hybrid (14 chromosomes)
1
2 Cell division error and self-fertilization
BB
Wild Triticum
(14 chromo-
somes)
Wild T. tauschii (14 chromosomes)
T. turgidum Emmer wheat (28 chromosomes)
Figure 14.7_2
DD
ABD
3 Hybridization
Wild T. tauschii (14 chromosomes)
T. turgidum Emmer wheat (28 chromosomes)
Sterile hybrid (21 chromosomes)
Cell division error
and self-fertilization
AABBDD
T. aestivum Bread wheat (42 chromosomes)
4
AABB
14.8 Isolated islands are often showcases of speciation
Most of the species on Earth are thought to have originated by allopatric speciation.
Isolated island chains offer some of the best evidence of this type of speciation.
Multiple speciation events are more likely to occur in island chains that have
– physically diverse habitats,
– islands far enough apart to permit populations to evolve in isolation, and
– islands close enough to each other to allow occasional dispersions between them.
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14.8 Isolated islands are often showcases of speciation
The evolution of many diverse species from a common ancestor is adaptive radiation.
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,
– 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 around-
the-world voyage on the Beagle.
These finches
– 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
Cactus-seed-eater (cactus finch)
Tool-using insect-eater (woodpecker finch)
Seed-eater (medium ground finch)
Figure 14.8_1
Cactus-seed-eater (cactus finch)
Figure 14.8_2
Tool-using insect-eater (woodpecker finch)
Figure 14.8_3
Seed-eater (medium ground finch)
Peter and Rosemary Grant have worked
– for more than three decades,
– on medium ground finches, and
– on tiny, isolated, uninhabited Daphne Major in the Galápagos Islands.
14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches
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Medium ground finches and cactus finches occasionally interbreed. Hybrids
– have intermediate bill sizes,
– survive well during wet years, when there are plenty of soft, small seeds around,
– are outcompeted by both parental types during dry years, and
– can introduce more genetic variation on which natural selection acts.
14.9 SCIENTIFIC DISCOVERY: A long-term field study documents evolution in Darwin’s finches
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Figure 14.9
Larger
Smaller
Me
an
be
ak
siz
e
Large beaks can
crack large
seeds
Severe
drought
1980 1985 1990
Year
Smaller beaked
G. fortis can feed
on small seeds
Severe
drought
1995 2000
Competitor species,
G. magnirostris
Arrival of
new species
1975 2005
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
Over time in hybrid zones
– reinforcement may strengthen barriers to reproduction,
such as occurs in flycatchers, or
– fusion may reverse the speciation process as gene flow
between species increases, as may be occurring among
the cichlid species in Lake Victoria.
In stable hybrid zones, a limited number of hybrid
offspring continue to be produced.
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Three
populations
of a species
Figure 14.10A
Newly formed
species
Population Barrier to
gene flow
Gene
flow
Hybrid
individual
Hybrid
zone 1 2
4
3
Gene flow
Figure 14.10B
Male
collared
flycatcher
Male
pied
flycatcher
Allopatric
populations
Sympatric
populations
Pied flycatcher
from allopatric
population
Pied flycatcher
from sympatric
population
Figure 14.10B_1
Male
collared
flycatcher
Male
pied
flycatcher
Allopatric
populations
Sympatric
populations
Figure 14.10B_2
Pied flycatcher
from allopatric
population
Figure 14.10B_3
Pied flycatcher
from sympatric
population
Figure 14.10C
Pundamilia nyererei Pundamilia pundamilia
Hybrid: Pundamilia “turbid water”
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
– experience relatively little change for the rest of their existence.
2. Other species appear to have evolved more gradually.
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Animation: Macroevolution
Figure 14.11
Punctuated pattern
Gradual pattern
Time
14.11 Speciation can occur rapidly or slowly
What is the total length of time between speciation
events (between formation of a species and
subsequent divergence of that species)?
– In a survey of 84 groups of plants and animals, the time
ranged from 4,000 to 40 million years.
– Overall, the time between speciation events averaged 6.5
million years.
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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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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.
You should now be able to
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10. Describe the discoveries made by Peter and
Rosemary Grant in their work with Galápagos
finches.
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.
You should now be able to
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Figure 14.UN01
Zygote
Gametes Prezygotic barriers Postzygotic barriers
Viable,
fertile
offspring • Habitat isolation
• Temporal isolation
• Behavioral isolation
• Mechanical isolation
• Gametic isolation
• Reduced hybrid
viability
• Reduced hybrid
fertility
• Hybrid breakdown
Figure 14.UN02
b. a.
Original population
Figure 14.UN03
Species
may interbreed in a
b. c. d.
a.
outcome may be
f.
when
are
when
are
reproductive barriers
when
a few hybrids
continue to be produced
species separate
speciation is reversed
keeps and
e.
Figure 14.UN03_1
Species
may interbreed in a
b. c. d.
a.
outcome may be
Figure 14.UN03_2
b. c. d.
f.
when
are
when
are
reproductive barriers
when
a few hybrids
continue to be produced
species separate
speciation is reversed
keeps and
e.
Figure 14.10UN
Fusion Reinforcement Stability
Figure 14.10UN_1
Reinforcement
Figure 14.10UN_2
Fusion
Figure 14.10UN_3
Stability