Allopatric speciation: vicariance

1
Speciation in animals

• Allopatric speciation vicariance
• Biogeography
• Colonisation of Surtsey 1963-2003
• Sympatric speciation
• Rhagoletis pomonella
• Parapatric speciation
• Carrion crow hooded crow

2
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

3
Sympatric speciation

• Speciation in the absence of spatial isolation
• Polymorphism established ? selection favouring
  prezygotic isolation
• Genetic causes pleiotropy hitch-hiking

4
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

5
Rhagoletis pomonella sympatric speciation via
host shift

• Today hawthorn vs. apple associated R. pomonella
  populations genetically distinct

6
Parapatric speciation

• Adjacent but non-overlapping distributions
• Allopatric minus the geographical barrier
• Clines
• Reproductive barriers? sub species, hybrids
• Hybrid zone
• Rapid speciation in the face of environmental
  change?

7
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