Natural Selection and Speciation

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Natural Selection and Speciation
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Another way to look at it

• Directional Selection

Fitness
Trait
Trait
Negative Directional Selection
Positive Directional Selection
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• Stabilizing selection

Fitness
average trait value
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Egg laying wasp that eventually kills the cactus
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• Disruptive Selection

Fitness
average trait value
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Black-bellied seed cracker (Pyrenestes ostrinus)
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• Smith, T. B. 1990. Evolution. 44(4)832
• Black-bellied seed crackers (Pyrenestes) in
  Cameroon

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Same birds different studyOpen portion of bar
Number hatchedBlack portion of bar Number
survived
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Two more types of selection

• Correlational working on combinations of traits
  at once.

(body size)
(Wing length)
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• Frequency Dependent Selection Level of
  selection dependent upon most common phenotype
  (at the time)

Genyochromis Scale eater
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Scalebiters frequency dependent selection
Right mouthedness
Left mouthedness
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Frequency of left mouthedness
Frequency of right mouthedness
Time
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• Selection can lead to speciation
• Speciation
• Splitting of one species into two or more species
• Transformation of one species into a new species
  over time

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Anagenetic (gradual) versus Cladistic
(punctuated) Speciation
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Species

• Many, many definitions
• Biological species definition A group of
  actually or potentially breeding individuals
  which are reproductively isolated from all other
  groups.
• Doesnt work in all situations
• Fossils
• Asexual organisms

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Isolating mechanisms

• Prezygotic
• Postzygotic -

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• Pre-zygotic barriers include
• Temporal isolation
• Behavioral
• Mechanical
• Gametic

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Prezygotic I.M.s

• Habitat isolation
• Dendroica warblers in Eastern US

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Modes of speciation

• Allopatric allo different, patri fatherland
• Sympatric sym together
• Has to do with location or habitat

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Speciation only occurs with reproductive
isolation
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Sympatric speciation

• Polyploidy in plants
• Hybrids

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Adaptive Radiation

• Evolution of ecological ( morphological)
  diversity within a rapidly speciating lineage.

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• Hawaiian honeycreepers

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