Transcript hybrid zone

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 24
The Origin of Species
物種的起源
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: That “Mystery of Mysteries”
• In the Galápagos Islands Darwin discovered
plants and animals found nowhere else on
Earth
© 2011 Pearson Education, Inc.
Figure 24.1
• Speciation種化, 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微演化 consists of changes
in allele frequency in a population over time
• Macroevolution巨幅演化 refers to broad
patterns of evolutionary change above the
species level
© 2011 Pearson Education, Inc.
Animation: Macroevolution
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Concept 24.1: The biological species
concept emphasizes reproductive isolation
• Species is a Latin word meaning “kind”
or “appearance”
• Biologists compare morphology,形態
physiology生理, biochemistry生化, and
DNA sequences核酸序列 when
grouping organisms
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The Biological Species Concept
生物學種概念
• 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
生物學種概念強調基因流
© 2011 Pearson Education, Inc.
Figure 24.2
(a) Similarity between different species
(b) Diversity within a species
Reproductive Isolation
• Reproductive isolation生殖隔離 is the
existence of biological factors (barriers) that
impede two species from producing viable,
fertile offspring
• Hybrids雜交 are the offspring of crosses
between different species
• Reproductive isolation can be classified by
whether factors act before or after
fertilization
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Figure 24.3_a
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
(a)
Gametic
Isolation
Mechanical
Isolation
Behavioral
Isolation
Individuals
of
different
species
Postzygotic barriers
MATING
ATTEMPT
(c)
(d)
(e)
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(f)
(g)
(h)
(i)
(j)
(b)
(k)
(l)
• Prezygotic barriers block fertilization from
occurring by:合子前隔離阻斷受精作用
– Impeding different species from
attempting to mate 無法相遇
– Preventing the successful completion of
mating無法受精
– Hindering fertilization if mating is
successful受精卵無法發育
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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
• 棲所隔離：兩群個體生活於不同空間，導致
無法相遇(即使無生理障礙)
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Figure 24.3a
(a)
• Temporal isolation: Species that breed
at different times of the day, different
seasons, or different years cannot mix
their gametes雜交
• 時間隔離：由於日周活動或季節性活動
不同，導致無法交配
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Figure 24.3c
(c)
• Behavioral isolation: Courtship rituals and
other behaviors unique to a species are
effective barriers
• 行為隔離：求偶或其他特定行為形成有效阻
隔作用
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Figure 24.3e
(e)
• Mechanical isolation: Morphological
differences can prevent successful mating
• 機械隔離：形態不同導致無法成功交配
© 2011 Pearson Education, Inc.
Figure 24.3f
(f)
• Gametic Isolation: Sperm of one species
may not be able to fertilize eggs of another
species
• 配子隔離：精卵無法成功受精
© 2011 Pearson Education, Inc.
Figure 24.3g
(g)
Figure 24.3_b
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
Individuals
of
different
species
(a)
MATING
ATTEMPT
(c)
(d)
(b)
Gametic
Isolation
Mechanical
Isolation
Behavioral
Isolation
(e)
(f)
FERTILIZATION
(g)
• Postzygotic barriers prevent the hybrid
zygote from developing into a viable, fertile
adult:合子後隔離阻斷胚胎發育或後代受孕
– Reduced hybrid viability雜交不成
– Reduced hybrid fertility雜交不孕
– Hybrid breakdown雜交中斷
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• Reduced hybrid viability雜交不成: Genes
of the different parent species may interact
and impair the hybrid’s development
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Figure 24.3h
(h)
• Reduced hybrid fertility雜交不孕:
Even if hybrids are vigorous, they may
be sterile
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Figure 24.3i
(i)
• Hybrid breakdown雜交中斷: Some firstgeneration hybrids are fertile, but when
they mate with another species or with
either parent species, offspring of the next
generation are feeble or sterile
© 2011 Pearson Education, Inc.
Figure 24.3l
(l)
Figure 24.3_c
Postzygotic barriers
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(h)
(i)
(j)
(k)
(l)
Limitations of the Biological Species Concept
• The biological species concept cannot
be applied to fossils or asexual
organisms (including all prokaryotes)
• The biological species concept
emphasizes absence of gene flow
• However, gene flow can occur between
distinct species
– For example, grizzly bears北美灰熊
and polar bears北極熊can mate to
produce “grolar bears北極灰熊 ”
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Figure 24.4
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear”
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
–形態學種概念強調結構特徵，適用於有
性生殖與無性生殖物種
© 2011 Pearson Education, Inc.
• 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 生態學種概念強調棲地
• The phylogenetic species concept defines a
species as the smallest group of individuals on
a phylogenetic tree 種系遺傳學種概念
– It applies to sexual and asexual species,
but it can be difficult to determine the
degree of difference required for separate
species
© 2011 Pearson Education, Inc.
Concept 24.2: Speciation can take place
with or without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation異域種化
– Sympatric speciation同域種化
© 2011 Pearson Education, Inc.
Figure 24.5
(a) Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
(b) Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.
Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is
interrupted or reduced when a
population is divided into geographically
isolated subpopulations
– For example, the flightless
cormorant鸕鶿 of the Galápagos
likely originated from a flying
species on the mainland
© 2011 Pearson Education, Inc.
The Process of Allopatric Speciation
• The definition of barrier depends on the
ability of a population to disperse
– For example, a canyon may create a
barrier for small rodents, but not birds,
coyotes, or pollen
© 2011 Pearson Education, Inc.
Figure 24.6
A. harrisii
A. leucurus
• Separate populations may evolve
independently through mutation, natural
selection, and genetic drift
• Reproductive isolation may arise as a result
of genetic divergence
– For example, mosquitofish in the Bahamas
comprise several isolated populations in
different ponds
© 2011 Pearson Education, Inc.
Figure 24.7
(a) Under high predation
(b) Under low predation
Evidence of Allopatric Speciation
• 15 pairs of sibling species of snapping
shrimp 槍蝦 (Alpheus) are separated by the
Isthmus of Panama
• These species originated 9 to 13 million
years ago, when the Isthmus of Panama
formed and separated the Atlantic and
Pacific waters
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Figure 24.8
A. formosus
A. nuttingi
Atlantic Ocean
Isthmus of Panama
Pacific Ocean
A. panamensis
A. millsae
Figure 24.8c
A. formosus
Figure 24.8d
A. panamensis
Figure 24.8e
A. nuttingi
Figure 24.8f
A. millsae
• Regions with many geographic barriers
typically have more species than do
regions with fewer barriers
• Reproductive isolation between
populations generally increases as the
distance between them increases
– For example, reproductive isolation
increases between dusky salamanders
脊口螈(蠑螈) that live further apart
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Degree of reproductive isolation
Figure 24.9
2.0
1.5
1.0
0.5
0
0
50
100
150
200
250
Geographic distance (km)
300
• Barriers to reproduction are intrinsic;
separation itself is not a biological
barrier
© 2011 Pearson Education, Inc.
EXPERIMENT
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised on
maltose medium
Some flies raised
on starch medium
Mating experiments
after 40 generations
RESULTS
Female
22
9
8
20
Male
Maltose
Starch
Starch
population 1 population 2
Number of matings
in experimental group
Starch
Starch
population 2 population 1
Starch
Starch
Male
Female
Maltose
Figure 24.10
18
15
12
15
Number of matings
in control group
Figure 24.10a
EXPERIMENT
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised on
maltose medium
Some flies raised
on starch medium
Mating experiments
after 40 generations
Figure 24.10b
RESULTS
Female
Maltose
22
9
8
20
Number of matings
in experimental group
Starch
Starch
population 2 population 1
Starch
Starch
Starch
population 1 population 2
Male
Male
Maltose
Starch
Female
18
15
12
15
Number of matings
in control group
Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes
place in geographically overlapping
populations
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Polyploidy 多套性
• Polyploidy is the presence of extra sets
of chromosomes due to accidents
during cell division
• Polyploidy is much more common in
plants than in animals
• An autopolyploid自體多套性 is an
individual with more than two
chromosome sets, derived from one
species
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• An allopolyploid異體多套性 is a
species with multiple sets of
chromosomes derived from different
species
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Figure 24.11-1
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Figure 24.11-2
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Figure 24.11-3
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Normal
gamete
n=3
Unreduced gamete
with 7 chromosomes
Figure 24.11-4
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Normal
gamete
n=3
Unreduced gamete
with 7 chromosomes
New species:
viable fertile hybrid
(allopolyploid) 2n = 10
• 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
• For example, the North American maggot fly
can live on native hawthorn trees as well as
more recently introduced apple trees
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Sexual Selection
• Sexual selection can drive sympatric
speciation
• Sexual selection for mates of different colors
has likely contributed to speciation in cichlid
fish in Lake Victoria
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Figure 24.12
EXPERIMENT
Normal light
P. pundamilia
P. nyererei
Monochromatic
orange light
Allopatric and Sympatric Speciation:
A Review
• In allopatric speciation, geographic
isolation restricts gene flow between
populations
• Reproductive isolation生殖隔離 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
生殖隔離一旦形成即使棲群個體再相遇 亦
不能繁殖
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• 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
© 2011 Pearson Education, Inc.
Concept 24.3: Hybrid zones reveal factors
that cause reproductive isolation
• A hybrid zone雜交帶 is a region in which
members of different species mate and
produce hybrids
• Hybrids are the result of mating between
species with incomplete reproductive
barriers
© 2011 Pearson Education, Inc.
Patterns Within Hybrid Zones
• A hybrid zone can occur in a single band
where adjacent species meet
– For example, two species of toad in the genus
Bombina鈴蟾 interbreed in a long and narrow
hybrid zone
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Figure 24.13
EUROPE
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad, Bombina bombina
火腹蟾蜍
Yellow-bellied
toad, Bombina
variegata
多彩鈴蟾.
Frequency of
B. variegata-specific allele
Yellow-bellied
toad range
0.99
Hybrid
zone
0.9
Yellow-bellied
toad range
0.5
Fire-bellied
toad range
0.1
0.01
40
10
0
20
10
20
30
Distance from hybrid zone center (km)
Figure 24.13a
EUROPE
Fire-bellied
toad range
Hybrid zone
Yellow-bellied
toad range
Frequency of
B. variegata-specific allele
Figure 24.13b
0.99
Hybrid
zone
0.9
Yellow-bellied
toad range
0.5
Fire-bellied
toad range
0.1
0.01
40
30
10
0
20
10
20
Distance from hybrid zone center (km)
• Hybrids often have reduced fitness
compared with parent species
• The distribution of hybrid zones can be more
complex if parent species are found in
patches within the same region
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Hybrid Zones over Time
• When closely related species meet in a
hybrid zone, there are three possible
outcomes:
– Reinforcement
– Fusion
– Stability
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Figure 24.14-1
Gene flow
Population
Barrier to
gene flow
Figure 24.14-2
Isolated
population
diverges
Gene flow
Population
Barrier to
gene flow
Figure 24.14-3
Isolated
population
diverges
Hybrid
zone
Gene flow
Population
Barrier to
gene flow
Hybrid
individual
Figure 24.14-4
Possible
outcomes:
Isolated
population
diverges
Hybrid
zone
Reinforcement
OR
Fusion
OR
Gene flow
Population
Barrier to
gene flow
Hybrid
individual
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
– For example, in populations of flycatchers鶲
鳥 , males are more similar in allopatric
populations than sympatric populations
© 2011 Pearson Education, Inc.
Figure 24.15
Females choosing between
these males:
28
Number of females
24
Females choosing between
these males:
Sympatric pied male
Allopatric pied male
Sympatric collared male
Allopatric collared male
20
16
12
8
4
(none)
0
Own
species
Other
species
Female mate choice
Own
species
Other
species
Female mate choice
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
• For example, researchers think that
pollution in Lake Victoria has reduced
the ability of female cichlids to
distinguish males of different species
• This might be causing the fusion of
many species
© 2011 Pearson Education, Inc.
Figure 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
• 雜交帶若有外來的、廣泛的基因流，則增加
生殖隔離機制
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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
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The Time Course of Speciation
• 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
• 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 equilibria 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
© 2011 Pearson Education, Inc.
Figure 24.17
(a) Punctuated
pattern
Time
(b) Gradual
pattern
Speciation Rates 種化速率
• The punctuated pattern in the fossil record
and evidence from lab studies suggest that
speciation can be rapid
– For example, the sunflower Helianthus
anomalus originated from the hybridization of
two other sunflower species
© 2011 Pearson Education, Inc.
Figure 24.18
Figure 24.19
EXPERIMENT
H. annuus
gamete
H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
RESULTS
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
Figure 24.19a
EXPERIMENT
H. annuus
gamete
H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
Figure 24.19b
RESULTS
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
• The interval between speciation events can
range from 4,000 years (some cichlids) to
40 million years (some beetles), with an
average of 6.5 million years
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Studying the Genetics of Speciation
• A fundamental question of evolutionary
biology persists: How many genes change
when a new species forms?
• Depending on the species in question,
speciation might require the change of only
a single allele or many alleles
– For example, in Japanese Euhadra snails, the
direction of shell spiral affects mating and is
controlled by a single gene
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• In monkey flowers (Mimulus), two loci affect
flower color, which influences pollinator
preference猴面花(溝酸漿屬)
• Pollination that is dominated by either
hummingbirds or bees can lead to
reproductive isolation of the flowers
• In other species, speciation can be
influenced by larger numbers of genes and
gene interactions
© 2011 Pearson Education, Inc.
Figure 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
© 2011 Pearson Education, Inc.
Figure 24.UN01
Cell
division
error
2n = 6
Tetraploid cell
4n = 12
2n
2n
Gametes produced
by tetraploids
New species
(4n)
Figure 24.UN02
Original population
Allopatric speciation
Sympatric speciation
Figure 24.UN03
Ancestral species:
Triticum
monococcum
(2n = 14)
Wild
Triticum
(2n = 14)
Product:
T. aestivum
(bread wheat)
(2n = 42)
Wild
T. tauschii
(2n = 14)