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Chapter 24
The Origin of Species
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
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Overview: That “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on
Earth
Video: Galápagos Tortoise
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Fig. 24-1
• Speciation - origin of new species
• Evolutionary theory must explain how new
species originate and how populations evolve
Animation: Macroevolution
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The Biological Species Concept
• Biological species concept - a species is a
group of populations whose members have the
potential to interbreed & produce viable, fertile
offspring
• they do not breed successfully with other
populations
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Fig. 24-2a
(a) Similarity between different species
Fig. 24-2b
(b) Diversity within a species
Reproductive Isolation
• Reproductive isolation - existence of
biological factors (barriers) that impede two
species from producing viable, fertile offspring
• Hybrids - offspring of crosses between
different species
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• 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
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• Habitat isolation: Two species encounter
each other rarely, or not at all, because they
occupy different habitats
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• Temporal isolation: Species that breed at
different times of the day, different seasons, or
different years cannot mix their gametes
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Fig. 24-4e
(c)
Eastern spotted skunk
(Spilogale putorius)
Fig. 24-4f
(d)
Western spotted skunk
(Spilogale gracilis)
• Behavioral isolation: Courtship rituals and
other behaviors unique to a species are
effective barriers
Video: Albatross Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
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Fig. 24-4h
(f)
Mechanical isolation: Morphological differences can
prevent successful mating
Bradybaena with shells
spiraling in opposite
directions
• Gametic isolation: Sperm of one species may
not be able to fertilize eggs of another species
Sea urchins
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• Postzygotic barriers prevent the hybrid
zygote from developing into a viable, fertile
adult
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• Reduced hybrid viability: Genes of the
different parent species may interact and
impair the hybrid’s development
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Fig. 24-4l
(h)
Ensatina hybrid
• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile
Horse
Donkey
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Mule (sterile hybrid)
• Hybrid breakdown: 1st
generation hybrids are
fertile, but the next
generation are feeble or
sterile
Hybrid cultivated rice plants with
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Cummings
stunted
offspring (center)
Fig. 24-4a
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Individuals
of
different
species
(a)
Mating
attempt
(c)
(d)
(b)
Mechanical Isolation
Behavioral Isolation
(e)
(f)
Fig. 24-4i
Prezygotic barriers
Gametic Isolation
Postzygotic barriers
Reduced Hybrid Viability Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(j)
(k)
(l)
Concept 24.2: Speciation can take place with or
without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
– Sympatric speciation
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Fig. 24-5
(a) Allopatric speciation
(b) Sympatric speciation
Allopatric (“Other Country”) Speciation
• Allopatric speciation, gene flow is interrupted
when a population is divided into
geographically isolated subpopulations
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Sympatric (“Same Country”) Speciation
• Sympatric speciation - speciation takes place
in geographically overlapping populations
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Polyploidy
• Polyploidy is the presence of extra sets of
chromosomes due to accidents during cell
division
• An autopolyploid is an individual with more
than two chromosome sets, derived from one
species
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Fig. 24-10-1
2n = 6
4n = 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
Fig. 24-10-2
2n = 6
4n = 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
2n
Gametes
produced
are diploid..
Fig. 24-10-3
2n = 6
4n = 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
2n
Gametes
produced
are diploid..
4n
Offspring with
tetraploid
karyotypes may
be viable and
fertile.
• An allopolyploid is a species with multiple
sets of chromosomes derived from different
species
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Fig. 24-11-1
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Meiotic
error
Species A
2n = 6
Normal
gamete
n=3
Fig. 24-11-2
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Meiotic
error
Species A
2n = 6
Normal
gamete
n=3
Hybrid
with 7
chromosomes
Fig. 24-11-3
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Meiotic
error
Species A
2n = 6
Normal
gamete
n=3
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n=3
Fig. 24-11-4
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Meiotic
error
Species A
2n = 6
Normal
gamete
n=3
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n=3
Viable fertile
hybrid
(allopolyploid)
2n = 10
• Polyploidy is much more common in plants
than in animals
• Many important crops (oats, cotton, potatoes,
tobacco, and wheat) are polyploids
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Habitat Differentiation
• Sympatric speciation can also result from the
appearance of new ecological niches
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Sexual Selection
• Sexual selection can drive sympatric speciation
• Sexual selection for mates of different colors
has likely contributed to the speciation in cichlid
fish in Lake Victoria
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Fig. 24-13
EUROPE
Fire-bellied
toad range
Hybrid zone
0.99
Allele frequency (log scale)
Yellow-bellied toad,
Bombina variegata
Yellow-bellied
toad range
Fire-bellied toad,
Bombina bombina
0.9
0.5
0.1
0.01
40
20
30
10
0
10
20
Distance from hybrid zone center (km)
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
• Broad patterns in speciation can be studied
using the fossil record, morphological data, or
molecular data
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Patterns in the Fossil Record
• Fossil record includes examples of species that
appear suddenly, persist unchanged for some
time, and then disappear
• Punctuated equilibrium - periods of apparent
stasis punctuated by sudden change
• The punctuated equilibrium model contrasts
with a model of gradual change in a species’
existence
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Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
You should now be able to:
1. Define and discuss the limitations of the four
species concepts
2. Describe and provide examples of prezygotic
and postzygotic reproductive barriers
3. Distinguish between and provide examples of
allopatric and sympatric speciation
4. Explain how polyploidy can cause
reproductive isolation
5. Define the term hybrid zone and describe
three outcomes for hybrid zones over time
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings