Transcript Origin of Species

Chapter 24
The Origin of Species
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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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
• Evolutionary theory must explain how new species
originate and how populations evolve
• 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
Animation: Macroevolution
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LE 24-2
Anagenesis
Cladogenesis
Concept 24.1: The biological species concept
emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance”
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The Biological Species Concept
• Members of a biological species are
reproductively compatible, at least potentially; they
cannot interbreed with other populations.
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LE 24-3
Similarity between different species.
Diversity within a 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 and 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
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• Habitat isolation: Two species encounter each
other rarely, or not at all, because they occupy
different habitats, even though not isolated by
physical barriers
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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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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective
barriers
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mechanical isolation: Morphological differences
can prevent successful mating
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Gametic isolation: Sperm of one species may not
be able to fertilize eggs of another species
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual
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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
• 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
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• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile
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• Hybrid breakdown: Some first-generation hybrids
are fertile, but when they mate with another
species or with either parent species, offspring of
the next generation are feeble or sterile
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Limitations of the Biological Species Concept
• The biological species concept does not apply to
– Asexual organisms
– Fossils
– Organisms about which little is known
regarding their reproduction
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Other Definitions of Species
• Morphological: defines a species by structural
features
• Paleontological: focuses on morphologically
discrete species known only from the fossil record
• Ecological: views a species in terms of its
ecological niche
• Phylogenetic: defines a species as a set of
organisms with a unique genetic history
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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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LE 24-5
Allopatric speciation
Sympatric speciation
Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is interrupted or
reduced when a population is divided into
geographically isolated subpopulations
• One or both populations may undergo
evolutionary change during the period of
separation
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LE 24-6
A. harrisi
A. leucurus
• To determine if allopatric speciation has occurred,
reproductive isolation must have been established
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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
• An autopolyploid is an individual with more than
two chromosome sets, derived from one species
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LE 24-8
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
4n
• An allopolyploid is a species with multiple sets of
chromosomes derived from different species
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LE 24-9
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Unreduced gamete
with 7 chromosomes
Viable fertile hybrid
(allopolyploid)
Meiotic error;
Species A chromosome
number not
2n = 4
reduced from
2n to n
2n = 10
Normal gamete
n=3
Species B
2n = 6
Normal gamete
n=3
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
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LE 24-10
P. pundamilia
P. nyererei
Normal light
Monochromatic orange light
Allopatric and Sympatric Speciation: A Summary
• In allopatric speciation, a new species forms while
geographically isolated from its parent population
• In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
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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
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LE 24-12
Dubautia laxa
KAUAI
5.1
million
years
1.3
million
years
MOLOKAI
MAUI
OAHU
3.7 LANAI
million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Studying the Genetics of Speciation
• The explosion of genomics is enabling
researchers to identify specific genes involved in
some cases of speciation
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The Tempo of Speciation
• The fossil record includes many episodes in which
new species appear suddenly in a geologic
stratum, persist essentially unchanged through
several strata, and then apparently disappear
• 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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Evolutionary Novelties
• Most novel biological structures evolve in many
stages from previously existing structures
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• Some complex structures, such as the eye, have
had similar functions during all stages of their
evolution
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LE 24-14
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Patch of pigmented cells
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
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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
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LE 24-15b
Chimpanzee fetus
Chimpanzee adult
Human adult
Human fetus
Comparison of chimpanzee and human skull growth
• Heterochrony has also played a part in the
evolution of salamander feet
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LE 24-16
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
• Substantial evolutionary change can also result
from alterations in genes that control the
placement and organization of body parts
• Homeotic genes determine such basic features as
where wings and legs will develop on a bird or
how a flower’s parts are arranged
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• The products of one class of homeotic genes
called Hox genes
• Hox genes provide positional information in the
development of fins in fish and limbs in tetrapods
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LE 24-18
Chicken leg bud
Region of
Hox gene
expression
Zebrafish fin bud
• Evolution of vertebrates from invertebrate animals
was associated with alterations in Hox genes
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LE 24-19
Hypothetical vertebrate
ancestor (invertebrate)
with a single Hox cluster
First Hox
duplication
Hypothetical early
vertebrates (jawless)
with two Hox clusters
Second Hox
duplication
Vertebrates (with jaws)
with four Hox clusters
Evolution Is Not Goal Oriented
• The fossil record often shows apparent trends in
evolution that may arise because of adaptation to
a changing environment
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LE 24-20
Recent
Equus
Hippidion and other genera
Pleistocene
Nannippus
Pliohippus
Hipparion Neohipparion
Pliocene
Sinohippus
Megahippus
Callippus
Archaeohippus
Merychippus
Miocene
Anchitherium
Hypohippus
Parahippus
Miohippus
Oligocene
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Eocene
Pachynolophus
Orohippus
Key
Hyracotherium
Grazers
Browsers
• According to the species selection model, trends
may result when species with certain
characteristics endure longer and speciate more
often than those with other characteristics
• The appearance of an evolutionary trend does not
imply that there is some intrinsic drive toward a
particular phenotype
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