Speciation in animals Crucial event:Reproductive isolation 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
Today: hawthorn vs. apple associated R. pomonella populations genetically distinct Rhagoletis pomonella: sympatric speciation via host shift
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?
Interbreeding occurs in hybrid zone speciation incomplete? A hybrid zone is also a tension zone if the hybrids are selectively disadvantageous The hybrid zone of the hooded and carrion crows (Corvus corone & C. corax) in Europe