Download Allopatric speciation

Module 1: Evolution
Month Day Topic
Sept
8
Mechanisms of evolution I
11
Mechanisms of evolution II
13
Speciation
15
Macroevolution
18
Biodiversity
20
The history of plants
22
Molecular evolution
25
27
Exam review
First mid-term exam
Microevolution
Change in the frequencies of genotypes
in a population
Macroevolution
The formation of new species
Species A
Species B
Time
Species A
Species B
Species A
Species A
Species B
Species C
Time
A species is...
a group of actually or potentially
interbreeding natural populations
that are reproductively isolated from
other such groups.
A species is...
a group of actually or potentially
interbreeding natural populations
that are reproductively isolated from
other such groups.
A species is...
a group of actually or potentially
interbreeding natural populations
that are reproductively isolated from
other such groups.
A species is...
a group of actually or potentially
interbreeding natural populations
that are reproductively isolated from
other such groups.
But what about asexual
organisms?
How do new species form?
When gene flow ends between natural
populations
and
their gene pool changes
Once a barrier to gene flow is
established...
populations diverge because of
microevolution
How do new species form?
1. Allopatric speciation
2. Sympatric speciation
3. Parapatric speciation
1. Allopatric speciation
•
Literally “other country”
1. Allopatric speciation
•
Literally “other country”
•
Geographic barrier divides population
or
Part of population crosses barrier and
“founds” new population
1. Allopatric speciation
•
Literally “other country”
•
Geographic barrier divides population
or
Part of population crosses barrier and
“founds” new population
•
Most prevalent form of speciation
Allopatric speciation
• Geographic barrier
divides population
• Gene flow is cut off
• Microevolution takes over
• Populations differentiate
Fig. 19-1, p.300
Housefinch (Carpodacus)
Fig. 19-7d13, p.305
Iiwi (Vestiaria coccinea)
Fig. 19-7d12, p.305
2. Sympatric speciation
• Literally “same country”
2. Sympatric speciation
• Literally “same country”
• Species arise from a connected population
2. Sympatric speciation
• Literally “same country”
• Species arise from a connected population
• Most common in plants
2. Sympatric speciation
• Literally “same country”
• Species arise from a connected population
• Most common in plants
• Occasionally seen in animals
Speciation by polyploidy
(plants)
• Mistake during cell division
Speciation by polyploidy
(plants)
• Mistake during cell division
• New individual is viable but genetically
isolated
Speciation by polyploidy
(plants)
• Mistake during cell division
• New individual is viable but genetically
isolated
• In plants, individual with new ploidylevel can often self-fertilize
Speciation by polyploidy
T. aestivum (one of the
common bread wheats)
Triticum monococcum
(einkorn)
T. tauschii
(a wild relative)
Unknown species
of wild wheat
14AA
X
14BB
14AB
T. turgidum
(wild emmer)
28AABB
X
cross-fertilization, followed by a
spontaneous chromosome
doubling
14DD
42AABBDD
Speciation by behavioral
change (animals)
• Parents make “mistake”
Speciation by behavioral
change (animals)
• Parents make “mistake”
• Young pattern on a new place
Speciation by behavioral
change (animals)
• Parents make “mistake”
• Young pattern on a new place
• Young return to place to mate
Speciation by behavioral
change (animals)
• Parents make “mistake”
• Young pattern on a new place
• Young return to place to mate
• No gene flow with original population
3. Parapatric speciation
•
Like allopatric speciation, except
boundary is not physical
3. Parapatric speciation
•
Like allopatric speciation, except
boundary is not physical
•
Parts of a population experience
different conditions
3. Parapatric speciation
•
Like allopatric speciation, except
boundary is not physical
•
Parts of a population experience
different conditions
•
Natural selection is stronger than gene
flow
Parapatric speciation
Bullock’s oriole
Baltimore oriole
hybrid zone
Can species interbreed if they
get back together?
Species of European and American sycamores have been
separated for 20 million years, yet they can still interbreed
Reproductive barriers
between species
• Prezygotic barriers
– barriers that prevent mating
Reproductive barriers
between species
• Prezygotic barriers
– barriers that prevent mating
• Postzygotic barriers
– Barriers that operate after mating occurs
Prezygotic barriers
•
•
•
•
•
Behaviorial isolation
Ecological isolation
Temporal isolation
Mechanical isolation
Gametic isolation
Fig. 19-4c, p.302
Fig. 19-4d, p.302
Fig. 19-4e, p.302
Fig. 19-4b, p.302
Fig. 19-4a, p.302
Fig. 18-20, p.299
Postzygotic barriers
•
•
•
•
Hybrid abnormality
Hybrid infertility
Low hybrid viability
Absence or sterility of one sex
Fig. 19-21, p.317
What controls the rate at
which new species form?
What controls the rate at
which new species form?
• Species richness
What controls the rate at
which new species form?
• Species richness
• Range size and mobility
What controls the rate at
which new species form?
• Species richness
• Range size and mobility
• Behavior, especially mate choice
What controls the rate at
which new species form?
•
•
•
•
Species richness
Range size and mobility
Behavior, especially mate choice
Environmental change
What controls the rate at
which new species form?
•
•
•
•
•
Species richness
Range size and mobility
Behavior
Environmental change
Life history
What controls the rate at
which new species form?
•
•
•
•
•
•
Species richness
Range size and mobility
Behavior
Environmental change
Life history
“Empty space”
Hawaiian silverswords
4th mass extinction 210 mya: ~65% of species
5th mass extinction 65 mya: ~76% of species
Extraterrestrial impact or volcanism?
What controls the rate at
which new species form?
•
•
•
•
•
•
•
Species richness
Range size
Behavior
Environmental change
Generation time
“Empty space”
Innovation
Proportional Changes in Skull
Chimpanzee
Human
Figure 19.14b
Page 315