Download Allopatric speciation: forms a new species while geographically

Prezygotic barriers
Habitat
isolation
Temporal
isolation
Behavioral
isolation
Postzygotic barriers
Mechanical
isolation
Gametic
isolation
MATING
ATTEMPT
(a)
(c)
(e)
(f)
Reduced
hybrid
viability
Reduced
Hybrid
hybrid
breakdown
fertility
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(g)
(h)
(d)
(i)
(l)
(j)
(b)
(k)
(a) Similarity between different species
(b) Diversity within a species
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Grizzly bear (U. arctos)
Hybrid “grolar bear”
(a) Allopatric speciation: forms (b) Sympatric speciation: a subset
forms a new species without
a new species while
geographic separation.
geographically isolated.
Polar bear (U. maritimus)
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A. formosus
A. nuttingi
ATLANTIC
OCEAN
Isthmus of Panama
PACIFIC
OCEAN
(a) Under high predation:
(b) Under low predation:
body shape that enables
body shape that favors
rapid bursts of speed
long, steady swimming
A. panamensis
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A. millsae
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Experiment
Cell
division
error
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised
on starch medium
Some flies raised
on maltose medium
2n = 6
Mating experiments
after 40 generations
Tetraploid cell
4n = 12
Results
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8
20
Male
22
Starch
Starch
population 1 population 2
Starch
Starch
population 2 population 1
Starch
Male
Female
Maltose
Maltose
Female
Starch
Number of matings
in experimental group
18
15
12
15
2n
New species
(4n)
Gametes produced
Number of matings
in control group
7
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Species A
2n = 6
Species B
2n = 4
by tetraploids
Experiment
Meiotic error; chromosome
number not reduced from 2n to n
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Normal light
Monochromatic
orange light
Unreduced gamete
with 4 chromosomes
Normal
gamete
n=3
P. pundamilia
Hybrid with
7 chromosomes
Normal
gamete
n=3
Unreduced gamete
with 7 chromosomes
P. nyererei
New species:
viable fertile hybrid
(allopolyploid)
2n = 10
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Isolated
population
diverges.
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad, Bombina
bombina
Yellow-bellied toad, Bombina
variegata
Frequency of
B. variegata-specific allele
Yellow-bellied
toad range
Possible
outcomes:
Reinforcement
0.99
Hybrid
zone
Gene flow
Population
Barrier to
gene flow
0.9
Yellow-bellied
toad range
0.5
Fire-bellied
toad range
Fusion
Hybrid
individual Stability
0.1
0.01
40
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Hybrid
zone
30
20
10
0
10
20
Distance from hybrid zone center (km)
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(a) Punctuated model
Pundamilia nyererei
Pundamilia pundamilia
Time
Pundamilia “turbid water,”
hybrid offspring from a
location with turbid water
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(a) Mimulus lewisii
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(b) M. lewisii with
M. cardinalis allele
(c) Mimulus cardinalis (d) M. cardinalis with
M. lewisii allele
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(b) Gradual model
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