24lecturepresentation 100812184256-phpapp01

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Chapter 24
The Origin of Species

Overview: That “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on
Earth
Video: Galápagos TortoiseVideo: Galápagos Tortoise

• 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
Animation: MacroevolutionAnimation: Macroevolution

Concept 24.1: The biological species concept
emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance”
• Biologists compare morphology, physiology,
biochemistry, and DNA sequences when
grouping organisms

The Biological Species Concept
• The biological species concept states that a
species is a group of populations whose
members have the potential to interbreed in
nature and produce viable, fertile offspring;
they do not breed successfully with other
populations
• Gene flow between populations holds the
phenotype of a population together

Fig. 24-2
(a) Similarity between different species
(b) Diversity within a species

Fig. 24-2a
(a) Similarity between different species

Fig. 24-2b
(b) Diversity within a species

Fig. 24-3
EXPERIMENT
RESULTS
Example of a gene tree for population pair A-B
Allele Population
Gene flow event 1 B
B
B
B
5
6
7
2
3
4
A
A
A
Allele 1 is more closely related to
alleles 2, 3, and 4 than to
alleles 5, 6, and 7.
Inference: Gene flow occurred.
Alleles 5, 6, and 7 are more closely
related to one another than to
alleles in population A.
Inference: No gene flow occurred.
Pair of
populations
with detected
gene flow
Estimated minimum
number of gene flow
events to account for
genetic patterns
Distance between
populations (km)
A-B
K-L
A-C
B-C
F-G
G-I
C-E
5
3
2–3
2
2
2
1–2
340
720
1,390
1,190
1,110
760
1,310

Fig. 24-3a
EXPERIMENT
Example of a gene tree for population pair A-B
Allele Population
Gene flow event 1 B
B
B
B
5
6
7
2
3
4
A
A
A
Allele 1 is more closely related to
alleles 2, 3, and 4 than to
alleles 5, 6, and 7.
Inference: Gene flow occurred.
Alleles 5, 6, and 7 are more closely
related to one another than to
alleles in population A.
Inference: No gene flow occurred.

Fig. 24-3b
RESULTS
Pair of
populations
with detected
gene flow
Estimated minimum
number of gene flow
events to account for
genetic patterns
Distance between
populations (km)
A-B
K-L
A-C
B-C
F-G
G-I
C-E
5
3
2–3
2
2
2
1–2
340
720
1,390
1,190
760
1,110
1,310

Fig. 24-3c
Grey-crowned babblers

Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two
species from producing viable, fertile offspring
• Hybrids are the offspring of crosses between
different species
• Reproductive isolation can be classified by
whether factors act before or after fertilization

• 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

• Habitat isolation: Two species encounter
each other rarely, or not at all, because they
occupy different habitats, even though not
isolated by physical barriers

Fig. 24-4
Prezygotic barriers
Habitat Isolation
Individuals
of
different
species
Temporal Isolation Behavioral Isolation
Mating
attempt
Mechanical Isolation Gametic Isolation
Fertilization
Reduced Hybrid Viability Reduced Hybrid Fertility
Postzygotic barriers
Hybrid Breakdown
Viable,
fertile
offspring
(a)
(b)
(d)
(c) (e) (f) (g) (h) (i)
(j)
(l)
(k)

Fig. 24-4a
Habitat Isolation Temporal Isolation
Prezygotic barriers
Behavioral Isolation
Mating
attempt
Mechanical Isolation
(f)(e)(c)(a)
(b)
(d)
Individuals
of
different
species

Fig. 24-4i
Prezygotic barriers
Gametic Isolation
Fertilization
Reduced Hybrid Viability
Reduced Hybrid Fertility Hybrid Breakdown
Viable,
fertile
offspring
(g) (h) (i)
(j)
(l)
(k)

Fig. 24-4b
Prezygotic barriers
Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation
Individuals
of
different
species
Mating
attempt

Prezygotic barriers
Fig. 24-4j
Gametic Isolation
Fertilization
Reduced Hybrid Viability Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring

Fig. 24-4c
(a)
Water-dwelling Thamnophis

Fig. 24-4d
(b)
Terrestrial Thamnophis

• Temporal isolation: Species that breed at
different times of the day, different seasons, or
different years cannot mix their gametes

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: Blue-footed Boobies Courtship RitualVideo: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship RitualVideo: Giraffe Courtship Ritual
Video: Albatross Courtship RitualVideo: Albatross Courtship Ritual

Fig. 24-4g
(e)
Courtship ritual of blue-
footed boobies

• Mechanical isolation: Morphological
differences can prevent successful mating

Fig. 24-4h
(f)
Bradybaena with shells
spiraling in opposite
directions

• Gametic isolation: Sperm of one species may
not be able to fertilize eggs of another species

• Postzygotic barriers prevent the hybrid
zygote from developing into a viable, fertile
adult:
– Reduced hybrid viability
– Reduced hybrid fertility
– Hybrid breakdown

• Reduced hybrid viability: Genes of the
different parent species may interact and
impair the hybrid’s development

Fig. 24-4l
(h)
Ensatina hybrid

• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile

Fig. 24-4o
(k)
Mule (sterile hybrid)

• 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

Fig. 24-4p
(l)
Hybrid cultivated rice plants with
stunted offspring (center)

Limitations of the Biological Species Concept
• The biological species concept cannot be
applied to fossils or asexual organisms
(including all prokaryotes)

Other Definitions of Species
• Other species concepts emphasize the unity
within a species rather than the separateness
of different species
• The morphological species concept defines
a species by structural features
– It applies to sexual and asexual species but
relies on subjective criteria

• The ecological species concept views a
species in terms of its ecological niche
– It applies to sexual and asexual species and
emphasizes the role of disruptive selection
• The phylogenetic species concept: defines a
species as the smallest group of individuals on
a phylogenetic tree
– It applies to sexual and asexual species, but it
can be difficult to determine the degree of
difference required for separate species

Concept 24.2: Speciation can take place with or
without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
– Sympatric speciation

Fig. 24-5
(a) Allopatric speciation (b) Sympatric speciation

Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is
interrupted or reduced when a population is
divided into geographically isolated
subpopulations

The Process of Allopatric Speciation
• The definition of barrier depends on the ability
of a population to disperse
• Separate populations may evolve
independently through mutation, natural
selection, and genetic drift

Fig. 24-6
A. harrisi A. leucurus

Evidence of Allopatric Speciation
• Regions with many geographic barriers
typically have more species than do regions
with fewer barriers

Fig. 24-7
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
Millions of years ago (mya)
1 2 3
1 2 3
100 80 60 40 20 0
88 mya 65 mya 56 mya
India
Madagascar

Fig. 24-7a
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
Millions of years ago (mya)
100 80 60 40 20 0
1 2 3

Fig. 24-7b
India
88 mya 65 mya 56 mya
Madagascar
1 2 3

• Reproductive isolation between populations
generally increases as the distance between
them increases

Fig. 24-8
Geographic distance (km)
Degreeofreproductiveisolation
0
0
50 100 150 250200 300
0.5
1.0
1.5
2.0

• Barriers to reproduction are intrinsic;
separation itself is not a biological barrier

Fig. 24-9
EXPERIMENT
RESULTS
Initial population
Some flies
raised on
starch medium Mating experiments
after 40 generations
Some flies
raised on
maltose medium
Female
Female
Starch
Starch Starch
Maltose population 1 population 2
Male
StarchMaltose
Male
StarchStarch
population1population2
22
8 20
9 18
12
15
15
Mating frequencies
in experimental group
Mating frequencies
in control group

Fig. 24-9a
EXPERIMENT
Initial population
Some flies
raised on
starch medium Mating experiments
after 40 generations
Some flies
raised on
maltose medium

Fig. 24-9b
RESULTS
Female
Female
Starch
Starch Starch
Maltose population 1 population 2
Male
StarchMaltose
Male
StarchStarch
population1population2
22
8 20
9 18
12
15
15
Mating frequencies
in experimental group
Mating frequencies
in control group

Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes
place in geographically overlapping
populations

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

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

Fig. 24-11-1
Species A
2n = 6
Normal
gamete
n = 3
Meiotic
error
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes

Fig. 24-11-2
Species A
2n = 6
Normal
gamete
n = 3
Meiotic
error
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Hybrid
with 7
chromosomes

Fig. 24-11-3
Species A
2n = 6
Normal
gamete
n = 3
Meiotic
error
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n = 3

Fig. 24-11-4
Species A
2n = 6
Normal
gamete
n = 3
Meiotic
error
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
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

Habitat Differentiation
• Sympatric speciation can also result from the
appearance of new ecological niches
• For example, the North American maggot fly
can live on native hawthorn trees as well as
more recently introduced apple trees

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

Fig. 24-12
EXPERIMENT
Normal light
Monochromatic
orange light
P.
pundamilia
P. nyererei

Allopatric and Sympatric Speciation: A Review
• In allopatric speciation, geographic isolation
restricts gene flow between populations
• Reproductive isolation may then arise by
natural selection, genetic drift, or sexual
selection in the isolated populations
• Even if contact is restored between
populations, interbreeding is prevented

• In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
• Sympatric speciation can result from
polyploidy, natural selection, or sexual
selection

Concept 24.3: Hybrid zones provide opportunities
to study factors that cause reproductive isolation
• A hybrid zone is a region in which members of
different species mate and produce hybrids

Patterns Within Hybrid Zones
• A hybrid zone can occur in a single band where
adjacent species meet
• Hybrids often have reduced fitness compared
with parent species
• The distribution of hybrid zones can be more
complex if parent species are found in multiple
habitats within the same region

Fig. 24-13
EUROPE
Fire-bellied
toad range
Hybrid zone
Yellow-bellied
toad range
Yellow-bellied toad,
Bombina variegata
Fire-bellied toad,
Bombina bombina
Allelefrequency(logscale)
Distance from hybrid zone center (km)
40 30 20 2010 100
0.01
0.1
0.5
0.9
0.99

Fig. 24-13a
Yellow-bellied toad,
Bombina variegata

Fig. 24-13b
Fire-bellied toad,
Bombina bombina

Fig. 24-13c
Fire-bellied
toad range
Yellow-bellied
toad range
Hybrid zone
Allelefrequency(logscale)
Distance from hybrid zone center (km)
40 30 20 2010 100
0.01
0.1
0.5
0.9
0.99

Hybrid Zones over Time
• When closely related species meet in a hybrid
zone, there are three possible outcomes:
– Strengthening of reproductive barriers
– Weakening of reproductive barriers
– Continued formation of hybrid individuals

Fig. 24-14-1
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow

Fig. 24-14-2
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Isolated population
diverges

Fig. 24-14-3
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Isolated population
diverges
Hybrid
zone
Hybrid

Fig. 24-14-4
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Isolated population
diverges
Hybrid
zone
Hybrid
Possible
outcomes:
Reinforcement
OR
OR
Fusion
Stability

Reinforcement: Strengthening Reproductive
Barriers
• The reinforcement of barriers occurs when
hybrids are less fit than the parent species
• Over time, the rate of hybridization decreases
• Where reinforcement occurs, reproductive
barriers should be stronger for sympatric than
allopatric species

Fig. 24-15
Sympatric male
pied flycatcher
Allopatric male
pied flycatcher
Pied flycatchers
Collared flycatchers
Numberoffemales
(none)
Females mating
with males from:
Own
species
Other
species
Sympatric males
Own
species
Other
species
Allopatric males
0
4
8
12
16
20
24
28

Fig. 24-15a
Sympatric male
pied flycatcher
Allopatric male
pied flycatcher

Fig. 24-15b
Pied flycatchers
Collared flycatchers
28
24
20
16
12
8
4
0
(none)
Numberoffemales
Females mating
with males from:
Own
species
Other
species
Sympatric males
Own
species
Other
species
Allopatric males

Fusion: Weakening Reproductive Barriers
• If hybrids are as fit as parents, there can be
substantial gene flow between species
• If gene flow is great enough, the parent species
can fuse into a single species

Fig. 24-16
Pundamilia nyererei Pundamilia pundamilia
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water

Stability: Continued Formation of Hybrid
Individuals
• Extensive gene flow from outside the hybrid
zone can overwhelm selection for increased
reproductive isolation inside the hybrid zone
• In cases where hybrids have increased fitness,
local extinctions of parent species within the
hybrid zone can prevent the breakdown of
reproductive barriers

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

The Time Course of Speciation
• Broad patterns in speciation can be studied
using the fossil record, morphological data, or
molecular data

Patterns in the Fossil Record
• The fossil record includes examples of species
that appear suddenly, persist essentially
unchanged for some time, 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

Fig. 24-17
(a) Punctuated pattern
(b) Gradual pattern
Time

Speciation Rates
• The punctuated pattern in the fossil record and
evidence from lab studies suggests that
speciation can be rapid
• The interval between speciation events can
range from 4,000 years (some cichlids) to
40,000,000 years (some beetles), with an
average of 6,500,000 years

Fig. 24-18
(a) The wild sunflower Helianthus anomalus
H. anomalus
H. anomalus
H. anomalus
(b) The genetic composition of three chromosomes in H.
anomalus and in experimental hybrids
Chromosome 1
Chromosome 2
Chromosome 3
Experimental hybrid
Experimental hybrid
Experimental hybrid
Key
Region diagnostic for
parent species H. petiolaris
parent species H. annuus
Region lacking information on parental origin

Fig. 24-18a
(a) The wild sunflower Helianthus anomalus

Fig. 24-18b
(b) The genetic composition of three chromosomes in H.
anomalus and in experimental hybrids
Region lacking information on parental origin
parent species H. petiolaris
parent species H. annuus
Key
Experimental hybrid
Experimental hybrid
Experimental hybrid
Chromosome 3
Chromosome 2
Chromosome 1
H. anomalus
H. anomalus
H. anomalus

Studying the Genetics of Speciation
• The explosion of genomics is enabling
researchers to identify specific genes involved
in some cases of speciation
• Depending on the species in question,
speciation might require the change of only a
single allele or many alleles

Fig. 24-20
(a) Typical Mimulus lewisii (b) M. lewisii with an M. cardinalis flower-color allele
(c) Typical Mimulus cardinalis (d) M. cardinalis with an M. lewisii flower-color allele

From Speciation to Macroevolution
• Macroevolution is the cumulative effect of
many speciation and extinction events

Fig. 24-UN1
Original population
Allopatric speciation Sympatric speciation

Fig. 24-UN2
Ancestral species:
Triticum
monococcum
(2n = 14)
AA BB
Wild
Triticum
(2n = 14)
Product:
AA BB DD
T. aestivum
(bread wheat)
(2n = 42)
Wild
T. tauschii
(2n = 14)
DD

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

24lecturepresentation 100812184256-phpapp01

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