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Chapter 24
The Origin of Species
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: The “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on Earth
Video: Galápagos Tortoise
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• Speciation, the origin of new species, is at the
focal point of evolutionary theory
• Microevolution consists of adaptations that
evolve within a population, confined to one gene
pool
• Macroevolution refers to evolutionary change
above the species level
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• Two basic patterns of evolutionary change:
–
Anagenesis (phyletic evolution) transforms
one species into another
– Cladogenesis (branching evolution) is the
splitting of a gene pool, giving rise to one or
more new species
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Animation: Macroevolution
The Biological Species Concept
• Members of a biological species are
reproductively compatible, at least potentially; they
cannot interbreed with other populations.
Similarity between different species.
Diversity
within a
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Benjamin Cummings
species.
Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two species
from producing viable, fertile hybrids
• Two types of barriers:
– Prezygotic
– Postzygotic
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• Prezygotic barriers impede mating or hinder
fertilization if mating does occur:
– Habitat isolation
– Temporal isolation
– Behavioral isolation
– Mechanical isolation
– Gametic isolation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 24-4a
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Habitat
isolation
Temporal
isolation
Behavioral
isolation
Individuals
of
different
species
Mechanical
isolation
Gametic
isolation
Mating
attempt
HABITAT ISOLATION
Fertilization
TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION
GAMETIC ISOLATION
Postzygotic barriers prevent a hybrid zygote from
developing into a viable, fertile adult
Reduced
hybrid
viability
Reduced
hybrid
fertility
Hybrid
breakdown
Viable,
fertile
offspring
Fertilization
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN
• Temporal isolation: Species that breed at
different times of the day, different seasons, or
different years cannot mix their gametes
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• Behavioral isolation:
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mechanical isolation:
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gametic isolation:
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 24-4aa
Prezygotic barriers impede mating or hinder fertilization if mating does occur
Habitat
isolation
Individuals
of
different
species
HABITAT ISOLATION
Temporal
isolation
Behavioral
isolation
Mechanical
isolation
Mating
attempt
TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION
Gametic
isolation
Fertilization
GAMETIC ISOLATION
LE 24-4ab
Postzygotic barriers prevent a hybrid zygote from
developing into a viable, fertile adult
Reduced
hybrid
viability
Reduced
hybrid
fertility
Hybrid
breakdown
Viable,
fertile
offspring
Fertilization
REDUCED HYBRID
VIABILITY
REDUCED HYBRID
FERTILITY
HYBRID BREAKDOWN
• Postzygotic barriers prevent the hybrid zygote
from developing into a viable, fertile adult:
– Reduced hybrid viability
– Reduced hybrid fertility
– Hybrid breakdown
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• Reduced hybrid viability: Genes of the different
parent species may interact and impair the
hybrid’s development
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hybrid breakdown: when hybrids mate with
either parent species, offspring of the next
generation are feeble or sterile
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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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Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is interrupted
or reduced when a population is divided into
geographically isolated subpopulations
A. harrisi
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A. leucurus
LE 24-7a
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies
raised on
starch medium
Mating experiments
after several generations
Some flies
raised on
maltose medium
LE 24-7b
22
9
8
20
Mating frequencies
in experimental group
Male
Same
Different
populations population
Male
Maltose Starch
Female
Starch Maltose
Female
Different
Same
population populations
18
15
12
15
Mating frequencies
in control group
Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place
in geographically overlapping populations
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Polyploidy
• Polyploidy is presence of extra sets of
chromosomes due to accidents during cell division
• It has caused the evolution of some plant species
Failure of cell division
in a cell of a growing
diploid plant after
chromosome duplication
gives rise to a tetraploid
branch or other tissue.
2n = 6
Gametes produced by
flowers on this
tetraploid branch are
diploid.
Offspring with
tetraploid karyotypes may be viable
and fertile—a new
biological species.
2n
4n = 12
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4n
Habitat Differentiation and Sexual Selection
• Sympatric speciation can also result from the
appearance of new ecological niches
• In cichlid fish, sympatric speciation has resulted
from nonrandom mating due to sexual selection
P. pundamilia
Normal light
P. nyererei
Monochromatic orange light
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Adaptive Radiation
• Adaptive radiation is the evolution of diversely
adapted species from a common ancestor upon
introduction to new environmental opportunities
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The Hawaiian archipelago is one of the world’s great
showcases of adaptive radiation
Dubautia laxa
KAUAI
5.1
million
years
1.3
million
MOLOKAI years
MAUI
OAHU
3.7 LANAI
million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
The Tempo of Speciation
• Niles Eldredge and Stephen Jay Gould coined the
term punctuated equilibrium to describe 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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LE 24-13
Time
Gradualism model
Punctuated equilibrium model
Concept 24.3: Macroevolutionary changes can
accumulate through many speciation events
• Macroevolutionary
change is cumulative
change during thousands
of small speciation
episodes
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Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Patch of pigmented cells
Some complex
structures, such as
the eye, have had
similar functions
during all stages of
their evolution
Fluid-filled cavity
Epithelium
Optic
nerve
Nerve fibers
Eyecup
Cellular
fluid
(lens)
Pigmented
layer (retina)
Pinhole camera-type eye
Optic nerve
Eye with primitive lens
Cornea
Lens
Retina
Optic nerve
Complex camera-type eye
Cornea
Evolution of the Genes That Control Development
• Genes that program development control the rate,
timing, and spatial pattern of changes in an
organism’s form as it develops into an adult
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Changes in Rate and Timing
• Heterochrony is an evolutionary change in the
rate or timing of developmental events
• It can have a significant impact on body shape
• Allometric growth is the proportioning that helps
give a body its specific form
Animation: Allometric Growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 24-15a
Newborn
2
15
5
Age (years)
Differential growth rates in a human
Adult
• Different allometric patterns contribute to the contrasting
shapes of human and chimpanzee skulls
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
Comparison of chimpanzee and human skull growth
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 24-16
Heterochrony has also
played a part in the
evolution of salamander
feet
Ground-dwelling salamander
Tree-dwelling salamander
• In paedomorphosis, the rate of reproductive
development accelerates compared with somatic
development
• The sexually mature species may retain body
features that were juvenile structures in an
ancestral species
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Changes in Spatial Pattern
• Homeotic genes determine such basic features
as where wings and legs will develop on a bird or
how a flower’s parts are arranged
– Hox genes provide positional information in
the development of fins in fish and limbs in
tetrapods
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Hox Genes
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LE 24-18
Chicken leg bud
Region of
Hox gene
expression
Zebrafish fin bud