Download Lecture 9-Reproductive Isolating Mechanisms

Speciation
&
Reproductive Isolating
Mechanisms
Speciation
Speciation is the origin of new species.
It can occur in several ways:
1. Allopatric speciation
2. Peripatric speciation
3. Parapatric speciation
4. Sympatric speciation
5. Artificial selection
6. Polyploidy
1. Allopatric speciation
A geographical barrier occurs in the population causing the population
to split. This prevents groups from mating with each other regularly,
eventually causing that lineage to speciation.
2. Peripatric speciation
Barrier
In Peripatric speciation, new species are formed in isolated peripheral
populations; this is similar to allopatric speciation in that populations are
isolated and prevented from exchanging genes.
3. Parapatric speciation
In parapatric speciation there is no specific geographic barrier to gene
flow. The population is continuous, but nonetheless, the population does
not mate randomly. Individuals are more likely to mate with their
geographic neighbors than with individuals in a different part of the
population's range.
4. Sympatric speciation
A new species is formed
from within its parent
population without
geographic separation.
5. Artificial selection
Speciation by polyploidy
More than the usual
number of chromosome
sets i.e. 3n, 4n.
Rare in animals,
causing death
Occurs in plants where
fruits and flowers of
polyploid plants are
healthier and larger than
normal.
Identify the following speciation types?
Allopatric speciation
Sympatric speciation
Diane Dodd’s experiment to show speciation
Diane Dodd’s fruit fly
experiment suggests that
isolating populations in
different environments
(e.g., with different food
sources) can lead to the
beginning of reproductive
isolation.
These results are
consistent with the idea
that geographic isolation
is an important step of
some speciation events.
Reproductive Isolating
Mechanisms
A. Pre-mating reproductive isolation mechanisms
1. Ecogeographic Isolation
2. Habitat Isolation
3. Seasonal Isolation
4. Behavioural Isolation
5. Mechanical Isolation
B. Post-mating reproductive isolation mechanisms
1. Gametic Isolation
2. Developmental Isolation
3. Hybrid inviability
4. Hybrid sterility
5. Selective Hybrid sterility
1. Ecogeographic Isolation
Two closely related species
Platanus occidentalis
Grows in the eastern US
Platanus orientalis
Grows in the eastern
Medeterranian region
2. Habitat Isolation
Two closely related species
Bufo americanus
Lives and breed in shallow
rain water ponds
Bufo fowleri (woodhousii)
Lives and breeds in slow flowing
streams
3. Seasonal Isolation
Two closely related species
Reticulotermes hageni
Mating flights occur in March- May
Reticulotermes virginicus
Mating flights occur in October- February
4. Behavioural Isolation
Normal crabs
Uca lactea - The Fidler crab
5. Mechanical Isolation
Etroplus suratensis and Etroplus maculatus
Post-mating reproductive
isolation mechanisms
1. Gametic Isolation
Drosophila vivilis
Drosophila americana
D. Vivilis males copulate with D. americana females, but the sperms are
killed due to the chemicals in the female reproductive tract
2. Developmental Isolation
Poecilia sp. Goby fishes living in the streams in
Central America, Mating between closely related species
possible. But deformed embroyns are formed.
3. Hybrid inviability
• Hybridization between closely related
species possible.
• But the F1 hybrids can not survive to
reproductive age
4. Hybrid sterility
Hybrid
Horse
Donkey
Mule
5. Selective Hybrid sterility