Speciation

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Speciation

• How do new species arise?

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What is a species?

• Species - a group of interbreeding individuals
  that share a gene pool and are reproductively
  isolated from other species.

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What is speciation?

• Speciation - the mechanism by which a new species
  is formed.
• Two types of speciation are
• Allopatric speciation
• Sympatric speciation

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Allopatric speciation

• Occurs when two populations are geographically
  isolated from one another. They are separated by
  distance or an impassable barrier.
• Allopatric
• (allo other, patric place)

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Allopatric speciation

• Occurs when a physical barrier cuts a breeding
  population in two.
• Example Grand Canyon squirrels

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2. Sympatric speciation

• New species develops when members of a population
  develop a genetic difference that prevents them
  from reproducing with members of the original
  species.
• Sympatric
• (sym same, patric place)

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Example Apple maggot flies.
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Sympatric Speciation

• Occurs due to reproductive isolation.
• Reproductive isolation may be caused by
• A) Pre-mating isolating mechanisms
• Example - Behavioural rituals
• - Differing mating seasons
• B) Post-mating isolating mechanisms
• Example - prevention of insemination
• - offspring may be sterile

C) Polyploidy
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C) Polyploidy

• An increase in the of chromosomes beyond the
  diploid number.
• Results from non-disjunction of chromosomes
  during meiosis or mitosis. May also result if
  cytokinesis doesnt occur.

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Adaptive Radiation

• All of these mechanisms to speciation can lead to
  adaptive radiation.
• Adaptive radiation is the emergence of numerous
  species from a common ancestor that spreads to
  new environments.
• Example - Darwins finches.