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1.3 Barriers to gene flow - Coggle Diagram
1.3 Barriers to gene flow
Geographical
Are extrinsic
Could be mountain ranges, rivers or any feature of the environment
Physically separate 2 populations
Example! North American Elk (
Cervus canadensis
) and European Red Deer (
Cervus elaphus
) can interbreed but are separated by sea/ocean/great distance.
A. K. A. Allopatric speciation
In a sense is just a 'first step' towards speciation as reproductive isolation must subsequently occur
Reproductive
in species that have not been separated is called sympatric separation
Premating
Ecological
Temporal isolation
Species don't mate because mating occurs at different times for them
Flowers
Pollinator isolation
Flowering plants that do not cross because they attract different pollinators
Monkeyflowers
Habitat isolation
Species don't physically interact because they mate in different locales
Fruit flies (drosophila)
Behavioural
Species don't mate because they don't recognise heterospecifics as mates
Frogs and fireflies
Post-mating-prezygotic
Mechanical isolation
Physical differences between species make mating or successful copulation impossible or dangerous
Carabus beetles
Gametic isolation
Fertilisation of the egg by the sperm fails. These could be due to being out-competed by conspecific mates, or due to incompatible surface proteins in the case off coral eggs.
North American field crickets (Allonemobius)
Post-zygotic
Hybrid inviability
The embryo fails to develop or the hybrid dies before reaching sexual maturity
Platyfish (Xiphophorus)
Theorised to be caused by 'speciation genes': population-specific alleles of genes common to both species that nevertheless are incompatible
Tend to be very rare
Hybrid sterility
The hybrid survives to sexual maturity, but is infertile
Mules and hinnies
Genetic incompatibility
Chromosomal incompatibility
Organelle incompstibility
Extrinsic inviability
The hybrid survives and is reproductively viable, but is at a competitive disadvantage in its environment.
Sticklebacks (Gasterosteus)
A. K. A. Isolating barriers/isolating mechanisns
Reinforcement
This is when geographically separate species are reunited but nevertheless continue to progress toward speciation
This is because natural selection renders hybrid populations 'unfit', and so they die out
Speciation:
Evolutionary mechanisms
Evolutionary change
Reproductive isolation
Speciation
Reproductive isolating barriers
Changes in genotypes and phenotypes
Natural/sexual selection
Mutation
Random genetic drift