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BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 14
The Origin of Species
Modules 14.1 – 14.9
From PowerPoint® Lectures for Biology: Concepts & Connections
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Evolution Underground
• Evolution has generally been thought of as a
very gradual process
– However, examples of rapid evolution have been
observed
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• One example of rapid evolution occurred
among mosquitoes that migrated into the
London underground
• In less than 150
years, Culex pipiens
evolved into a new
mosquito species,
Culex molestus
• The origin of new
species is called
speciation
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• The isolated mosquitoes adapted to their new
underground environment
– They altered their prey, mating habits, and
breeding patterns
• Environmental barriers that isolate
populations are just one of many mechanisms
in the evolution of species
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CONCEPTS OF SPECIES
14.1 What is a species?
• Carl Linnaeus used physical appearance to
identify species when he developed the
binomial system of naming organisms
– Example: Homo sapiens
– Taxonomy is the branch of biology concerned
with naming and classifying the diverse forms of
life.
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• But appearance alone does not always define a
species
– Example: eastern and western meadowlarks
Figure 14.1A
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• Similarities between some species and variation
within a species can make defining species
difficult
– Humans exhibit extreme physical diversity
Figure 14.1B
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• The biological species concept defines a species
as
– a population or group of populations whose
members can interbreed and produce fertile
offspring
– this concept also notes that considerable
variation can be exhibited
– Useful for looking for evidence of evolution as it
occurs.
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• A ring species may illustrate the process of
speciation: an application of the biological
species concept
1
OREGON
POPULATION
Sierra
Nevada
COASTAL
POPULATIONS
Yelloweyed
Yellowblotched
2
Gap in
ring
Monterey
INLAND
POPULATIONS
Largeblotched
3
Figure 14.1C
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• The biological species concept is not applicable
to fossils or asexual organisms
• Most organisms are classified based on
observable phenotypes
– The morphological species concept
• The genealogical species concept defines a
species as a cluster of organisms representing a
specific evolutionary lineage
• The ecological species concept defines a species
by its ecological role
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14.2 Reproductive barriers keep species separate
• Prezygotic and
postzygotic
reproductive
barriers prevent
individuals of
closely related but
different species
from interbreeding
even if there is no
geographic barrier
keeping them
apart.
Table 14.2
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• Courtship ritual in blue-footed boobies is an
example of one kind of prezygotic barrier,
behavioral isolation
• Many plant species have
flower structures that are
adapted to specific
pollinators, example of
mechanical isolation
• Differential timing of mating
(temporal isolation) like the
mosquitoes in the London
underground
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Figure 14.2A, B
• The complex structure of damselfly genitalia
forms a barrier to mating between separate
species of closely related Damselfly.
• Many species of sea urchin may live in close
association with each other on the floor of the
ocean. Male and female sea urchin reproduce
by releasing eggs and sperm into the water.
– Union of sperm and egg will only occur if they
are from the same species due to gametic
isolation
– Molecules on the surface of the egg must
recognize molecules on the surface of the sperm
cell in order for fertilization to occur
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• Postzygotic barriers prevent the development
of fertile adults
– Hybrid inviability: The hybrids do not live,
for example, when two different species of
frog mate but the hybrid does not survive.
– Hybrid sterility: The hybrids are not fertile,
such as when a female horse and a male
donkey mate to produce a sterile mule
– Hybrid breakdown: There is progressive
weakening of successive generations of
interbreeding hybrids. The first generation
of hybrids is fertile, but with subsequent
generations hybrid fitness declines.
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MECHANISMS OF SPECIATION
14.3 Geographic isolation can lead to speciation
• A key event in the evolution of many new species is the
separation of a population (and its gene pool) from other
populations of that species by a geographic barrier.
– The isolated population may become genetically unique as
its gene pool is changed by natural selection, genetic drift,
or mutation
– Allopatric speciation occurs when the gene pool
undergoes changes that create reproductive barriers
between the isolated population and its parent population
• Smaller, more
isolated populations
are more likely to
experience speciation
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Figure 14.3
14.4 Islands are living laboratories of speciation
• On the
Galápagos
Islands,
repeated
isolation and
adaptation
have resulted
in adaptive
radiation
of 14 species
of Darwin’s
finches
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Figure 14.4A
• Adaptive radiation on an island chain
1
A
Species A
from mainland
2
B
B
3
B
C
B
4
C
C D
C
C
D
D
5
Figure 14.4B
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• Each finch population adapted to its
environment in different ways
– Darwin noticed beak
differences.
– Finches living on islands
with hard seeds had big
tough beaks for cracking
– Finches feeding on insects
had smaller, sharper
beaks
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14.5 New species can also arise within the same
geographic area as the parent species
• In sympatric speciation, a new species may arise
without geographic isolation
– A failure in meiosis can produce diploid gametes
– Self-fertilization can then produce a tetraploid
zygote
Parent species
Zygote
Meiotic
error
Selffertilization
2n = 6
Diploid
Offspring may
be viable and
self-fertile
4n = 12
Tetraploid
Unreduced diploid gametes
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Figure 14.5A
• Most polyploids do not arise from a single
parent species
– Most are hybrids that would have been sterile
but experienced a mitotic or meiotic error
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14.6 Connection: Polyploid plants clothe and
feed us
• Many species of crop
plants are polyploid
– Oats, potatoes, coffee,
bananas, peanuts, plums,
apples, cotton, wheat
– They are the products of
hybridization and mitotic
or meiotic errors
– The modern bread wheat
is an example
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Figure 14.6A
14.7 Reproductive barriers may evolve as
populations diverge
• Flies were isolated
into separate
populations and
adapted to different
food sources
Initial sample
of fruit flies
Starch medium
Results of
mating experiments
Female
populations
Same
Different
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8
20
Mating frequencies
in experimental group
Same
9
Different
22
Male
populations
Female
Starch
Maltose
Male
Maltose Starch
• Starch flies prefer
other starch flies,
maltose flies prefer
other maltose flies
from any population
as long as they are
adapted to the same
food
Maltose medium
18
15
12
15
Mating frequencies
in control group
Figure 14.7A
– Pupfish in Death Valley became isolated in
separate springs in death valley due to climate
change. Some can no longer mate with other
pupfish from other springs.
Figure 14.7B
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14.8 The tempo of speciation can appear steady or
jumpy
• According to the
gradualist model of the
origin of species, as
postulated by Darwin,
– new species evolve by the
gradual accumulation of
changes brought about by
natural selection
• However, few gradual
transitions are found in
the fossil record
Figure 14.8A
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• The punctuated
equilibrium model
suggests that speciation
occurs in spurts
– Rapid change occurs
when an isolated
population diverges
from the ancestral
stock
– Virtually no change
occurs for the rest of
the species’ existence
Figure 14.8B
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14.9 Talking About Science: Peter and Rosemary
Grant study the evolution of Darwin’s finches
• The occasional
hybridization of finch
species adds to the
genetic variation of
parent populations
– This may have been
important in the
adaptive radiation
of finch species
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Figure 14.9
14.9 Talking About Science: Peter and Rosemary
Grant study the evolution of Darwin’s finches
• On a rare occurrence, a male of one species
mates with a female of another species
producing hybrids with intermediate beak
sizes.
– The size and shape of the finch beak dictates
the type of food consumed by the finch
– During drought years, the hybrids die because
they cannot compete with either of the parent
species for food, thus maintaining divergent
evolution of the finches.
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Fin(ch)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings