Download Sympatric speciation

Speciation in animals
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Allopatric speciation: vicariance
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Biogeography
 Colonisation
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Sympatric speciation
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of Surtsey 1963-2003
Rhagoletis pomonella
Parapatric speciation
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Carrion crow & hooded crow
Speciation in animals
Crucial event: Reproductive isolation (barrier to
gene flow)
•Prezygotic isolation
•Habitat, seasonal, sexual, mechanical, gamete
viability
•Postzygotic isolation
•Inviability or sterility of hybrids
Sympatric speciation
•Speciation in the absence of spatial isolation
•Polymorphism established  selection favouring
prezygotic isolation
•Genetic causes: pleiotropy & hitch-hiking
Rhagoletis pomonella:
sympatric speciation via host shift
•N. American R. pomonella lays
eggs in hawthorn fruit
•In 1864: R. pomonella first found
on apples in New York State
•Hawthorn  Apple host shift
Rhagoletis pomonella:
sympatric speciation via host shift
•Today: hawthorn vs. apple associated R. pomonella
populations genetically distinct
Parapatric speciation
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Adjacent but non-overlapping distributions
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–
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Reproductive barriers? – sub species,
hybrids
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Allopatric minus the geographical barrier
Clines
Hybrid zone
Rapid speciation in the face of
environmental change?
The hybrid zone of the hooded and carrion crows (Corvus corone &
C. corax) in Europe
•Interbreeding occurs in hybrid zone  speciation incomplete?
•A hybrid zone is also a tension zone if the hybrids are
selectively disadvantageous