Download SPECIATION Modes of

How a single species changes through time?
WHY
Speciation matters?
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• • • •
To understand how evolution has
produced the diversity of life, we need
to study two fundamental processes:
• • • •
To understand how evolution has
produced the diversity of life, we need
to study two fundamental processes:
• How a single species changes
through time?
• • • •
To understand how evolution has
produced the diversity of life, we need
to study two fundamental processes:
• How a single species changes
through time?
• How a single species becomes two
or more species? = speciation
SPECIES changes through
time
How a single species changes through time?
anagenesis - evolution
within a
species
lineage
Ponctuated EQUILIBRIUM
Punctuated equilibrium
Niles Eldredge & Steven J. Gould (1972).
Punctuated equilibrium: An alternative to phyletic
gradualism. pp. 82-115.
In: T. J. M. Schopf (ed.) Models in Paleobiology, Freeman, Cooper
& Co.,San Francisco.
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
How a single species becomes two or more species?
“... it is probable that the periods, during
which each [species] underwent
modification, though many and long as
measured by years, have been short in
comparison with the periods during
which each remained in an unchanged
condition.”
Charles Darwin, from the final 6th edition (1872)
of On the Origin of Species
Punctuated equilibrium predicts that a lot of evolutionary change takes place in short
periods of time tied to speciation events.
How a single species becomes two or more species?
How a single species becomes two or more species?
Punctuated equilibrium predicts that a lot of evolutionary change takes place in short
periods of time tied to speciation events.
How a single species becomes two or more species?
How a single species becomes two or more species?
How a single species becomes two or more species?
How a single species becomes two or more species?
How a single species becomes two or more species?
How a single species becomes two or more species?
How a single species becomes two or more species?
• • • •
To understand how evolution has
produced the diversity of life, we need
to study two fundamental processes:
• How a single species changes
through time?
• How a single species becomes two
or more species? = speciation
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Prezygotic
Isolation
Individuals
of
different
species
Barriers to REPRODUCTION
Habitat
isolation
Behavioral
Isolation
Mechanical
Isolation
ATTEMPT
MATING
Postzygotic
Gametic
Isolation
Reduced Hybrid
Viability
FERTILIZATION
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Reproductive Isolating Mechanisms
Prezygotic barriers
o Habitat/Geographic isolation
o Behavioral isolation
o Temporal isolation
o Mechanical isolation
o Gamete isolation
Prezygotic BARRIERS
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Geographical Isolation
Prezygotic Barriers
Habitat
Individuals
of different
species
Temporal
Behavioral
Mechanical
ATTEMPT
MATING
Gametic
FERTILIZATION
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Habitat Isolation
Sciurus aberti kaibabensis
Sciurus aberti
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Habitat Isolation
Water-dwellinggarter snake Thamnophis
Terrestrial Thamnophis
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Temporal Isolation
Breeds Jan - March
Temporal Isolation
Breeds late March - May
Bufo americanus
Eastern spotted skunk
(Spilogale putorius)
Western spotted skunk
(Spilogale gracilis)
mates in late summer
mates in late winter
Bufo fowleri
• • • •
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Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Behavioral isolation
Courtship Ritual
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Vocalization
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Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Mechanical Isolation
Genital openings
are not in
alignment
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Mechanical Isolation
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Marine
invertebrates and
other organisms
that lack mating
behavior: species
recognition occurs
between egg and
sperm
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Bindin
egg
surface
❚ Bindin is an adhesive protein
that binds sperm to the egg
surface. Without this,
fertilization does not occur.
❚ Rapid change of bindin
proteins creates barriers to
fertilization between species.
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Chromosome evolution in animals
Postzygotic BARRIERS
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Postzygotic
Barriers
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Reproductive Isolating Mechanisms
VIABLE,
FERTILE
OFFSPRING
Postzygotic barriers
o Reduced Hybrid Viability
o Reduced Hybrid Fertility
o Hybrid Breakdown
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Reduced Hybrid Viability
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Reduced Hybrid Fertility
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Hybrid Breakdown
• Speciation modes and tempo •
Modes of speciation
Speciation modes have been also classified
historically by the geographical arrangement of
populations undergoing the process, a classification
that focuses on the inhibitory effects of gene flow on
the evolution of reproductive isolation.
Modes of SPECIATION
Allopatry and sympatry
• Speciation modes and tempo •
• Speciation modes and tempo •
Evidence for two types of speciation
❚ It is thought that most speciation has been allopatric
❚ Sympatric speciation is thought to occur often among
flowering plants (2-4% of species formed through this
process)
The classic scenario of an ecological speciation
event, from beginning to end.
Reproductive isolation builds in allopatry
(green) as an incidental byproduct of
adaptation to alternative environments
(by-product mechanism). Reinforcement of
pre-mating isolation, driven by reduced hybrid
fitness, completes the speciation process
during the sympatric phase (blue). The timing
of secondary contact is flexible (indicated by
arrows at the boundary between the allopatric
and sympatric phases).
Schluter 2001. TREE
• Speciation modes and tempo •
How a single species becomes two or more species?
The Process of Speciation
One species
(set of
interbreeding
organisms)
Genetic variant spreads through
part of the species; bearers of this
variant must mate only with other
bearers of the same variant
Two species. Further
phenotypic, behavioural
and ecological
differences may evolve
• Speciation modes and tempo •
• Speciation modes and tempo •
Speciation is a 2-part process
Initially identical populations must diverge
Reproductive isolation must evolve to
maintain these differences
• Speciation modes and tempo •
Most
species
form when
geographic
barriers
block
genetic
exchange
• Speciation modes and tempo •
Allopatric
Peripatric
Parapatric
Sympatric
(allo = other,
patric = place)
(peri = near,
patric = place)
(para = beside,
patric = place)
(sym = same,
patric = place)
• Speciation modes and tempo •
• Speciation modes and tempo •
Isolated island
population
of kingfishers
Isolated island
population
of kingfishers
Mainland
population
of kingfishers
NEW
GUINEA
PACIFIC
OCEAN
Isolated island
population
of kingfishers
• Speciation modes and tempo •
Mainland
population
of kingfishers
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
Adaptive Radiation
Character Displacement
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• Speciation modes and tempo •
Adaptive Radiation: Character
Displacement:
• “Closely related
• “Natural selection
species that have
favors those
recently evolved
individuals that use
from a common
resources not used
ancestor by
by other species”
adapting to different
parts of the
environment”
ALLOPATRY
Vicariance
Ancestral population
Geographic isolation
Speciation
The geography of speciation
• Speciation modes and tempo •
1.A geographic barrier creates
isolation between two or more
portions of a population
The descendant populations
diverge genetically (due to drift
and selection)
The reproductive isolation is
completed
2.
3.
Allopatric speciation through
“dispersal and colonization”
• Speciation modes and tempo •
Isthmus of Panama
closed ~ 3.1 MYA
Split ~150
“geminate” (twin)
species
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
A. formosus
• Speciation modes and tempo •
A. nuttingi
P6
Knowlton et al.(1993) created a
phylogeny of Pacific (P) and Caribean
(C) species pairs of Alpheus
P6
C6
P3
In 6 out of 7 cases, the closest
relative of a species was on the other
side of the Isthmus
Atlantic Ocean
C3
C3
P5
C5
Isthmus of Panama
P4
C4
Pacific Ocean
P1
C1
P2
C2
Allopatric speciation
in snapping shrimp
Alpheus –
sibling species
P7
P7
A. panamensis
A. millsae
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• Speciation modes and tempo •
ALLOPATRY
A model for
adaptive
radiation on
island chains
Vicariance
Ancestral population
Geographic isolation
Speciation
Testing hypothesis in biogeography
ALLOPATRY
Dispersal
Species A’
Ancestral population
Geographic isolation
Testing hypothesis in biogeography
Species B
Speciation
Testing hypothesis in biogeography
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
Examples
Frequency of
alternative alleles
Diagnosing Models of
Speciation from Clinal
Variation
• Speciation modes and tempo •
• Speciation modes and tempo •
The descendant populations diverge
genetically due to:
D. heteroneura
D. silvestris
• Speciation modes and tempo •
drift and selection (unrelated to
interbreeding)
selection against hybridization
(reinforcement)
• Speciation modes and tempo •
How much isolation and for how long is needed for
allopatric speciation?
The reproductive isolation is completed
this occurs after “secondary contact” between allopatric
populations
a crucial step, why?
secondary contact is common
without complete reproductive barriers, species
will re-fuse
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Secondary contact and reinforcement
Secondary contact - contact between two populations that
have been isolated from each other and have been
diverging genetically for a while.
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Secondary contact and reinforcement
Secondary contact - contact between two populations that
have been isolated from each other and have been
diverging genetically for a while.
What happens after secondary contact depends on whether
reproductive isolating mechanisms have developed or not.
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Secondary contact and reinforcement
Secondary contact - contact between two populations that
have been isolated from each other and have been
diverging genetically for a while.
What happens after secondary contact depends on whether
reproductive isolating mechanisms have developed or not.
Reinforcement - the ways in which distinctness between
populations is maintained so as to prevent hybridization.
eg. lowered fitness of hybrid phenotypes.
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
• Speciation modes and tempo •
• Speciation modes and tempo •
Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids
Reinforcement example
• Speciation modes and tempo •
Populations
become sympatric
again and
interbreed.
Populations
become sympatric
again but do not
interbreed.
Speciation has not
occurred.
Speciation has
occurred.
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• Speciation modes and tempo •
Sympatric speciation
no geographic barrier
much rarer
shows how ecology can drive
speciation by selecting for assortative
mating
• Speciation modes and tempo •
• Speciation modes and tempo •
• Speciation modes and tempo •
Variation in Lake Malawi and
Lake Tanganyika Cichlids
New species - through sexual selection?
color polymorphism
fixation of color genes
through assortative mating
interruption of gene flow
population differentiation
⇓
species
• Speciation modes and tempo •
Peripatric Speciation
Peri and
Parapatry
An example of this is the London Underground mosquito, a variant of the mosquito
Culex pipiens, which entered in the London Undgerground in 19th century.
Evidence for its speciation includes genetic divergence, behavioural differences,
and difficulty in mating.
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• Speciation modes and tempo •
Examples
Parapatric Speciation
Although continuously distributed, different flowering times have begun to reduce
gene flow between metal-tolerant plants and metal-intolerant plants.
Human
Human
Human
Human
Human
Human