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Biology IB HL - 10.3 Speciation Part 3

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This deck covers key concepts of speciation, including prezygotic and postzygotic isolation, allopatric and sympatric speciation, and examples of reproductive barriers.

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What is postzygotic isolation?

Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
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Key Terms

Term
Definition
What is postzygotic isolation?
Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
How can prezygotic isolation barriers differ?
Prezygotic isolation barriers can be temporal, behavioural, geographic / ecological or mechanical
How can postzygotic isolation barriers differ?
whereas postzygotic isolation barriers include the inviability, infertility or breakdown of hybrid organisms
When does temporal isolation occur?
Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles
What is an example of temporal isolation?
Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed
When does behavioural isolation occur?
Behavioural isolation occurs when two populations exhibit different specific courtship patterns
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Biology IB HL - 10.3 Speciation Part 3
TermDefinition
What is postzygotic isolation?
Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
How can prezygotic isolation barriers differ?
Prezygotic isolation barriers can be temporal, behavioural, geographic / ecological or mechanical
How can postzygotic isolation barriers differ?
whereas postzygotic isolation barriers include the inviability, infertility or breakdown of hybrid organisms
When does temporal isolation occur?
Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles
What is an example of temporal isolation?
Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed
When does behavioural isolation occur?
Behavioural isolation occurs when two populations exhibit different specific courtship patterns
What is an example of behavioural isolation?
Certain populations of crickets may be morphologically identical but only respond to specific mating songs
When does geographical isolation occur?
Geographic isolation occurs when two populations occupy different habitats or separate niches within a common region
What is an example of geographic isolation?
Lions and tigers occupy different habitats and do not interbreed (usually)
What is hybrid inviability?
hybrids are produced but fail to develop to reproductive maturity
What is hybrid infertility?
hybrid fails to produce functional gametes (sterility)
What is hybrid breakdown?
F1 hybrids are fertile but F2 generation fails to develop properly
What is speciation?
Speciation is an evolutionary process that results in the formation of a new species from a pre-existing species
When does speciation occur?
It occurs when reproductive isolating mechanisms prevent two breeding organisms from producing fertile, viable offspring
What are the two basic mechanisms by which speciation can occur?
allopatric / sympatric speciation
What is allopatric speciation?
Allopatric speciation occurs when a geographical barrier physically isolates populations of an ancestral species
How do the two populations begin to separate in allopatric speciation?
The two populations begin to evolve separately as a result of cumulative mutation, genetic drift and natural selection
At what point does speciation occur in allopatric speciation?
Eventually the two populations reach a degree of genetic divergence whereby they can no longer interbreed (speciation)
What is sympatric speciation?
Sympatric speciation is divergence of species within the same geographical location (i.e. without a physical barrier)
What may sympatric speciation result from?
Sympatric speciation may result from the reproductive isolation of two populations as a result of genetic abnormalities
What is a typical error that causes sympatric speciation?
Typically, a chromosomal error may arise which prevents successful reproduction with any organism lacking the same error
What failure may cause sympatric speciation?
Sympatric speciation is most commonly caused as the result of a meiotic failure during gamete formation
What happens when meiotic cells fail to undergo cytokinesis (sympatric)?
If meiotic cells fail to undergo cytokinesis, chromosomal number will double in the gamete (e.g. diploid instead of haploid)
What will the offspring exhibit when cells do not undergo cytokinesis? (sympatric)
This will result in offspring that have additional sets of chromosomes (polyploidy)
When will speciation occur? (sympatric and meiosis)
Speciation will result if the polyploid offspring are viable and fertile but cannot interbreed with the original parent population