Origin of Species

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Origin of Species
Galapagos Tortoise
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Origin of Speciespatterns of speciation

• Anagenesis
• A single population is transformed enough to be
  designated a new species
• Cladogenesis
• Branching evolution. A new species arises from a
  small population that Buds from a parent
  species.
• Most species probably evolved this way. The
  branching evolution is the basis of biological
  diversity

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Two patterns of speciation
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Origin of SpeciesSpecies definitions

• Biological species a population whose members
  have the potential to interbreed with one another
  and produce viable, fertile offspring, but who
  cannot produce viable, fertile offspring with
  members of another species. (Reproductive
  Isolation)
• The biological species concept cannot be applied
  to asexually reproducing organisms
• Morphospecies species defined by their
  anatomical features

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The biological species concept is based on
interfertility rather than physical similarity
Eastern Meadowlark
Western Meadowlark
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Reproductive barriers

• Any factor that impedes two species from
  producing fertile hybrids
• Prevents interbreeding between closely related
  species
• Prezygotic barriers (impedes mating or hinders
  ova fertilization)
• Postzygotic barriers (after fertilization)

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Origin of SpeciesPrezygotic barriers

1. Habitat isolation
2. Temporal isolation
3. Behavioral isolation
4. Mechanical isolation
5. Gametic isolation

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Habitat Isolation
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Temporal Isolation
Late-winter mating season
Summer mating season
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Blue-footed boobies Courtship ritual as a
behavioral barrier between species.
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Mechanical Isolation
You cant fit a square peg in a round hole
Gametic Isolation
gamete recognition
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Origin of SpeciesPostzygotic barriers

1. Reduced hybrid viability (vigor)
2. Reduced hybrid fertility
3. Hybrid breakdown

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Origin of SpeciesIntrogression

• The transplantation of alleles between species.
• Alleles occasionally seep through all
  reproductive barriers and pass between gene pools
  of closely related species. May occur when a
  fertile hybrid mates successfully with one of the
  parent species.

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Liger
Hercules the liger

• Female Ligers are fertile and can reproduce. If a
  Female liger mated with a male tiger the
  offspring would have some lion genes. If that
  offspring could then mate with a tiger the lion
  genes would continue on within the Tiger Gene
  Pool, an example of introgression.

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A summary of reproductive barriers between
closely related species
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Origin of SpeciesModes of speciation

• Allopatric speciation
• A population forms a new species while
  geographically isolated from its parent
  population
• Sympatric speciation
• Species formation occurs in geographically
  overlapping populations

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Two modes of speciation
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Origin of Species Allopatric speciation

• occurs when the initial block to gene flow is a
  geographical barrier that physically isolates the
  population.
• The genetically isolated group can then follow
  its own evolutionary course as changes in allele
  frequencies occur and are undiluted by gene flow
  from other populations

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Has speciation occurred during geographic
isolation?
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Allopatric speciation of squirrels in the Grand
Canyon
White-tailed antelope squirrel (north rim)
Harriss antelope squirrel (south rim)
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Speciation in Galapagos Finches
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Speciation in Cichlids
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Origin of Species Allopatric speciation

• Adaptive Radiation emergence of numerous
  species from a common ancestor introduced into an
  environment.
• Example Darwins finches on the Galapagos island
  chain

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Adaptive Radiation of Galapagos Finches
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A model for adaptive radiation on island chains
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Adaptive Radiation in Cichlids(Specialization in
feeding)
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Origin of Species Sympatric speciation

• Formation of a new species within the
  geographical range of the parent population (no
  geographical isolation)
• Can occur quickly (in one generation) if a
  genetic change results in a reproductive barrier
  between mutants and the parent population

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Origin of Species Sympatric speciation
Iris

• Polyploid speciation
• Many plant species have originated from improper
  cell division that resulted in polypoidy
• Autopolyploidy an organism that has more than
  two chromosome sets, all derived from the same
  species
• Allopolyploidy a polyploid hybrid resulting
  from contributions by two different species. More
  common than autopolyploidy. Hybrids are usually
  sterile but may be very vigorous and propagate
  asexually.

Daylily
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Sympatric speciation by autopolyploidy in plants
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One mechanism for allopolyploid speciation in
plants
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Punctuated Equilibrium vs. Gradualism

• Punctuated equilibrium model suggests evolution
  occurring in spurts of relatively rapid change
  instead of gradual divergence

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Two models for the tempo of speciation