Speciation Flashcards
What are the types of reproductive isolation?
Geographic isolation
Behavioural isolation
Temporal isolation
What does the formation of a new species depend on?
Reproductive isolation
What are the three types of selection?
Stabilising selection - the mean phenotype is favoured
Directional selection - evolutionary change with a shift in the mean population phenotype
Disruptive/diverging/diversifying selection - two or more phenotypes are favoured and the mean phenotype is selected against
Which type of selection is speciation associated with?
Disruptive selection - causes divergence in phenotypes
It drives two or more peaks in fitness and when peaks have separated you may consider a new species formed
What can counter disruptive selection?
Gene flow
What is gene flow?
Exchange of genes between populations as a result of movement and interbreeding of individuals
What type of selection holds a species together? What other factor works with selection to ensure this?
Directional or stabilising selection
Work with gene flow
What are the two changes during speciation?
Divergence - species adapting to different selection pressures
Reproductive isolation - populations can no longer interbreed
What are the two main theories of speciation?
Allopatric speciation - geographic isolation and reproductive isoaltion FIRST, then divergence
Sympatric speciation - divergence FIRST, then reproductive isolation
What is phenotypic divergence from long-term isolation due to? (In allopatric speciation)
Different climatic or ecological conditions and so different selection pressures
Random genetic drift
When do we know speciation has occured?
If the geographical barrier between species has been removed they do not interbreed
Name an example of a possible current speciation?
Chaffinches
What does geographical isolation depend on?
Existence of physical barriers
An organisms dispersal ability
What type of selcetion causes allopatric speciation?
Disruptive
When does sympatric speciation happen?
When species are in contact with one another and can potentially interbreed and exchange genes
