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Chapter 24
The Origin of Species
物種源始
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
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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
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http://www.ecuador.us/images/mapgalap.gif
1
• Speciation, the origin of new species, is at the
focal point of evolutionary theory Ò 物種形成 / 種化
• Evolutionary theory must explain how new
species originate and how populations evolve
Ò 新種來源與種群發展
• Microevolution consists of adaptations that
evolve within a population, confined to one gene
pool Ò 源自於種群基因庫的微演化
• Macroevolution refers to evolutionary change
above the species level
Ò 巨演化 ---- 以種為基礎，包括了種、屬、科甚至界的新分類群
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http://www.nbb.cornell.edu/neurobio/hopkins/eodrecog/mormyridae.jpg
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Concept 24.1: The biological species concept
emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance” Ò 種的意義 1. 種類 2. 外觀
• Biologists compare morphology, physiology,
biochemistry, and DNA sequences when grouping
organisms
Ò 界定種類的依據來源多自下列方面進行比較 :
1. morphology 形態學
2. physiology 生理學
3. biochemistry 生物化學
4. DNA sequences DNA序列
5. others
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4
Concept 24.1: The biological species concept
emphasizes reproductive isolation
http://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/Mantella_madagascariensis01.jpg/300px-Mantella_madagascariensis01.jpg
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The Biological Species Concept 生物學的物種概念
• 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;
offspring they do not
breed successfully with other populations
• Gene flow between populations holds the
phenotype of a population together
Ò 自然狀態下交配繁衍
Ò 產生可存活並具有生殖能力之子代
Ò 不會與其他種群成功繁衍
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http://images.nbii.gov/RFemmer/D_preview-res/Diatoms-50-species-2.jpg
5
Fig. 24-2
(a) Similarity between different species
(b) Diversity within a species
http://genomebiology.com/2005/6/8/117
(a) Similarity between different species
(b) Diversity within a species
http://sciencenow.sciencemag.org/feature/science_shots/images/ss_2006531_1.jpg
http://andrewunknown.wordpress.com/tag/yen-carry/
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Fig. 24-3
EXPERIMENT
Example of a gene tree for population pair A-B
Allele
Gene flow event
Population
1
B
2
A
3
A
4
A
5
B
6
B
7
B
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.
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
5
340
K-L
3
720
A-C
2–3
1,390
B-C
2
1,190
F-G
2
760
G-I
2
1,110
C-E
1–2
1,310
Reproductive Isolation 生殖隔離
• 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
Ò 生殖隔離可以作用於授精前後
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Reproductive Isolation 生殖隔離
• Prezygotic barriers block fertilization from
occurring by: 合子前屏障
– Impeding different species from attempting to
mate Ò 阻礙交配企圖
– Preventing the successful completion of
mating Ò 阻礙交配過程
– Hindering fertilization if mating is successful
Ò 阻礙配子結合
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• Habitat isolation 棲地隔離
Two species encounter each other rarely, or not at
all, because they occupy different habitats, even
though not isolated by physical barriers
Ò 棲地狀態不同所造成的限制
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Fig. 24-4a
Prezygotic barriers
Temporal Isolation
Habitat Isolation
棲地隔離
時間隔離
Mechanical Isolation
Behavioral Isolation
機械性隔離
行為隔離
Individuals
of
different
species
Mating
attempt
(a)
(e)
(c)
(f)
(d)
(b)
Fig. 24-4i
Prezygotic barriers
Gametic Isolation
配子隔離
(g)
Postzygotic barriers
Reduced Hybrid Viability Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(h)
(i)
(l)
(j)
(k)
9
• Temporal isolation 時間隔離
Species that breed at different times of the day,
different seasons, or different years cannot mix their
gametes
Ò 繁殖季節不同所造成的限制
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Fig. 24-4e
(c)
Eastern spotted skunk
(Spilogale putorius)
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Fig. 24-4f
(d)
Western spotted skunk
(Spilogale gracilis)
• Behavioral isolation 行為隔離
Courtship rituals and other behaviors unique to a
species are effective barriers
Ò 不同的求偶訊息或行為
http://www.danheller.com/images/LatinAmerica/Ecuador/Galapagos/Birds/Frigatebird/frigatebird-1-big.jpg
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http://cas.bellarmine.edu/tietjen/Ethology/b01.gif
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Fig. 24-4g
(e)
Courtship ritual of blue-footed boobies
• Mechanical isolation 機械性隔離
Morphological differences can prevent successful
mating
Ò 不同型態造成無法成功交配
http://www3.sympatico.ca/tp.bridges/anableps1.jpg
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• Gametic isolation 配子隔離
Sperm of one species may not be able to fertilize
eggs of another species
Ò 雌雄配子無法成功結合所造成的限制
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Fig. 24-4k
(g)
Sea urchins
13
• Postzygotic barriers prevent the hybrid
zygote from developing into a viable, fertile
adult: 合子後屏障
– Reduced hybrid viability
Ò 削弱雜交種活存率
– Reduced hybrid fertility
Ò 削弱雜交種繁殖力
– Hybrid breakdown
Ò 雜交衰敗
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• Reduced hybrid viability
削弱雜交種活存率
Genes of the different parent species may interact
and impair the hybrid’s development
Ò異種交配形成雜交合子
Ò多具有遺傳不相容性 (genetic incompatibility)
Ò經常導致胚胎發育過程的中止
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Fig. 24-4l
(h)
Ensatina hybrid
• Reduced hybrid fertility
削弱雜交種繁殖率
Even if hybrids are vigorous, they may be sterile
Ò 即便雜交個體能活存
Ò 或許因為不具繁殖能力而無法延續種群
Ò 甚至無法與親代進行反交 (backbreed)
backbreed)
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http://www.aqua-pets.com.tw/aquapets/images/aq-pic/e-17/TN_1702-01.JPG
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• Reduced hybrid fertility
削弱雜交種繁殖率
Even if hybrids are vigorous, they may be sterile
Ò 即便雜交個體能活存
Ò 或許因為不具繁殖能力而無法延續種群
Ò 甚至無法與親代進行反交 (backbreed)
backbreed)
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• Hybrid breakdown
http://www.aqua-pets.com.tw/aquapets/images/aq-pic/e-17/TN_1702-01.JPG
雜交衰敗
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
Ò有時異種雜交產生的子代即便具有繁殖能力
Ò不論與自身相同的雜交種或任一親種交配
Ò其下一世代仍可能呈現虛弱或不孕
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16
Fig. 24-4p
(l)
Hybrid cultivated rice plants with
stunted offspring (center)
Fig. 24-4i
Prezygotic barriers
Gametic Isolation
Postzygotic barriers
Reduced Hybrid Viability Reduced Hybrid Fertility
削弱雜交活存率
Hybrid Breakdown
削弱雜交繁殖率
雜交衰敗
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(l)
(j)
(k)
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Limitations of the Biological Species Concept
生物學物種概念的限制條件
• The biological species concept cannot be applied
to fossils or asexual organisms (including all
prokaryotes)
Ò無法應用於化石種
Ò無法應用於行無性生殖的種類
(包含目前被認為較為高階的真核生物)
包含目前被認為較為高階的真核生物)
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http://anthropologynet.files.wordpress.com/2007/06/fossil-hominid-skulls.jpg
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 型態學物種概念
– It applies to sexual and asexual species but
relies on subjective criteria
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• The ecological species concept views a
species in terms of its ecological niche
生態學物種概念
– 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 系統發生學物種概念
– It applies to sexual and asexual species, but it
can be difficult to determine the degree of
difference required for separate species
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Concept 24.2: Speciation can take place with
or without geographic separation
• Speciation can occur in two ways:
– Allopatric speciation
Ò 異域種化
– Sympatric speciation
Ò 同域種化
種化的兩條路徑
http://upload.wikimedia.org/wikipedia/commons/0/05/Zh-Speciation_modes.svg.png
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Fig. 24-5
(a) Allopatric speciation
(b) Sympatric speciation
Allopatric (“Other Country”) Speciation
異域種化
• In allopatric speciation, gene flow is
interrupted or reduced when a population is
divided into geographically isolated
subpopulations
Ò種化發生於受地理分隔的種群
Ò遺傳交流被中斷或降低
Ò逐漸形成兩個亞種群 (subpopulation)
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http://pandasthumb.org/pt-archives/allopatry.jpg
20
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
Ò隔離屏障為種群難以突破的地理限制
Ò分隔後的種群各自獨立受到突變、天擇與遺傳漂變的影響
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Fig. 24-6
A. harrisi
A. leucurus
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Evidence of Allopatric Speciation
異域種化的實證
• Regions with many geographic barriers typically
have more species than do regions with fewer
barriers
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Fig. 24-7
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
100
60
80
1
2
40
20
0
3
Millions of years ago (mya)
1
3
2
India
Madagascar
88 mya
65 mya
56 mya
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Fig. 24-9
EXPERIMENT
Initial population
Some flies
raised on
starch medium
Mating experiments
after 40 generations
Some flies
raised on
maltose medium
RESULTS
Female
9
8
20
Male
22
Starch
Starch
population 1 population 2
Starch
Starch
population 2 population 1
Male
Maltose Starch
Female
Starch Maltose
Mating frequencies
in experimental group
18
15
12
15
Mating frequencies
in control group
Sympatric (“Same Country”) Speciation
同域種化
• In sympatric speciation, speciation takes place
in geographically overlapping populations
Ò 新物種衍生自親代族群
Ò 或稱同域種群
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http://pandasthumb.org/pt-archives/Sympatry.jpg
23
Polyploidy
多倍體
• Polyploidy is the presence of extra sets of
chromosomes due to accidents during cell
division Ò 細胞分裂時額外的染色體套數
• An autopolyploid is an individual with more than
two chromosome sets, derived from one species
Ò 同種多倍體 (autopolyploid)
1. 相同物種來源
2. 具備兩套以上 (非絕對偶數套數)
非絕對偶數套數)之染色體
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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.
24
• An allopolyploid is a species with multiple
sets of chromosomes derived from different
species
Ò 異種多倍體 (allopolyploid)
1. 較同種多倍體更為普遍
2. 由種間雜交 (interspecfic hybrids)產生
hybrids)產生
3. 形成多倍體之染色體源自不同物種
4. 子代通常不孕
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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
25
• Polyploidy is much more common in plants than
in animals Ò多倍體較易發生於植物
• Many important crops (oats, cotton, potatoes,
tobacco, and wheat) are polyploids
Ò許多重要之農作收成皆為多倍體
1.
2.
3.
4.
5.
Oats
Cotton
Potatoes
Tobacco
wheat
燕麥
棉花
馬鈴薯
菸草
小麥
http://www.freshchannels.com/image/nav/content/fresh_produce/photo/fc_potatoesInGroup.jpg
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Habitat Differentiation
棲地變異
• Sympatric speciation can also result from the
appearance of new ecological niches
Ò 同域種化創造新的生態區位
• 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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http://www.science.ca/images/Bernatchez_whitefish.gif
26
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
Ò 性擇可驅使同域種化
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Fig. 24-12
EXPERIMENT
Normal light
Monochromatic
orange light
P. pundamilia
P. nyererei
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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
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Allopatric and Sympatric Speciation: A Review
• 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
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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
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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
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29
Fig. 24-13
EUROPE
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad,
Bombina bombina
0.99
Allele frequency (log scale)
Yellow-bellied toad,
Bombina variegata
Yellow-bellied
toad range
0.9
0.5
0.1
0.01
40
20
30
10
0
10
20
Distance from hybrid zone center (km)
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
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30
Fig. 24-14-1
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Fig. 24-14-2
Isolated population
diverges
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
31
Fig. 24-14-3
Isolated population
diverges
Hybrid
zone
Gene flow
Hybrid
Population
(five individuals
are shown)
Barrier to
gene flow
Fig. 24-14-4
Isolated population
diverges
Possible
outcomes:
Hybrid
zone
Reinforcement
OR
Fusion
Gene flow
Hybrid
Population
(five individuals
are shown)
OR
Barrier to
gene flow
Stability
32
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
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Fig. 24-15
Sympatric male
pied flycatcher
28
Allopatric male
pied flycatcher
Pied flycatchers
Number of females
24
Collared flycatchers
20
16
12
8
4
(none)
0
Females mating Own
Other
with males from: species species
Sympatric males
Own
Other
species species
Allopatric males
33
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
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Fig. 24-16
Pundamilia nyererei
Pundamilia pundamilia
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water
34
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
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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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35
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 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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36
Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
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
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37
Fig. 24-18
(a) The wild sunflower Helianthus anomalus
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
H. anomalus
Chromosome 3
Experimental hybrid
Key
Region diagnostic for
parent species H. petiolaris
Region diagnostic for
parent species H. annuus
Region lacking information on parental origin
(b) The genetic composition of three chromosomes in H.
anomalus and in experimental hybrids
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
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38
Fig. 24-19
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
39
From Speciation to Macroevolution
• Macroevolution is the cumulative effect of many
speciation and extinction events
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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
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40