Hybrid Zone Dynamics

1
Hybrid Zone Dynamics
2
Geography of Speciation

• Allopatric Speciation populations geographically
  isolated
• split one population into two
• Sympatric Speciation evolution of reproductive
  barriers within a population
• no geographic isolation

3
Allopatric Speciation
Allopatric Speciation

• Biological barriers evolve between geographically
  isolated populations
• any physical barrier
• Depends on
• impermeability of barrier
• length of time barrier in place
• Gene flow sufficiently disrupted for genetic
  differences to accumulate

4
Sexual Selection

• Lead to phenotypic differences within species
• Can it lead to evolution of reproductive
  isolation between species?

5
Ecological Selection

• Can ecological differences cause reproductive
  isolation?
• Laboratory-isolated Drosophila and house flies
  selected for ecological differences
• Evolved prezygotic and postzygotic barriers
• Mimulus reproductively isolated by selection for
  different pollinators

bee pollinated
hummingbird pollinated
6
Reinforcement

• Reproductive isolation evolves as a direct
  adaption to reduce or eliminate less fit hybrids
• Reinforcement enhancement of prezygotic barriers
  due to selection against less fit hybrids
• May lead to evolution of character displacement

Hyla gratiosa
Hyla cinerea
7
Allopatric Speciation Evidence

• Sister species separated geographically
• barrier not always evident
• not necessarily isolated reproductively
• Many studies support evolution of reproductive
  isolation in allopatry

8
Sympatric Speciation
apple tree
hawthorne tree
Rhagoletis pomonella apple maggot fly