Speciation in animals Allopatric speciation: vicariance Biogeography Colonisation of Surtsey 1963-2003 Sympatric speciation Rhagoletis pomonella Parapatric speciation 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 Pleiotropy: Lets say that there is a gene controlling bird beak size. Selection on bird beak size due to efficiency of feeding (different food preferences) and also due to sexual choice. Therefore, an allele favoured due to an ecological adaptation (food preference) will also cause reproductive isolation due to sexual choice. Hitch-hiking: a gene at one locus is selected by natural selection, an allele at a linked locus simply rides along.

Sympatric speciation Speciation in the absence of spatial isolation Polymorphism established  selection favouring prezygotic isolation Genetic causes: pleiotropy & hitch-hiking Pleiotropy: Lets say that there is a gene controlling bird beak size. Selection on bird beak size due to efficiency of feeding (different food preferences) and also due to sexual choice. Therefore, an allele favoured due to an ecological adaptation (food preference) will also cause reproductive isolation due to sexual choice. Hitch-hiking: a gene at one locus is selected by natural selection, an allele at a linked locus simply rides along.

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 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?

The hybrid zone of the hooded and carrion crows (Corvus corone & C 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