Evolution Lecture 20: Adaptation

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Evolution Lecture 20 Adaptation
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What is adaptation?

• A trait or suite of traits that increases fitness
  of its possessor is called an adaptation
• A trait may be considered adaptive
• Individuals in past generations had variable
  traits, those traits that increased fitness were
  passed on in the highest number, thus adaptations
  evolve
• Demonstrating that certain traits are adaptive
  have dominated much of evolutionary literature
  over the past 140 years

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The adaptationist program

• Determining the function of a trait and then
  determining that individuals that posses the
  trait contribute more genes to future generations
  is the crux of the research for the adaptationist
• However, is it easy to determine that a trait is
  adaptive?
• No explanation for the adaptive value for a trait
  should be accepted b/c it is plausible and
  charming (Gould and Lewontin, 1979)

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Function of the neck in the Giraffe?
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Adaptive value of neck in giraffes?

• They tend not to feed at their maximum height,
  but rather in shrubs and bushes at the height of
  their shoulders
• Simmons and Scheepers suggest that males use
  their necks and heads as clubs during
  fightssometimes killing one another
• Their necks are 30-40cm longer 1.7x heavier than
  females, additionally the heads are more heavily
  armored
• Three classes of male giraffe sizes from large to
  small A, B and C
• Wins competitions AgtBgtC
• Number of successful mating attempts AgtBgtC

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Need to keep the following in mind when studying
adaptation

• Differences among populations or species may not
  be adaptive. Differences may be due to drift and
  have no function
• Not every trait or every use of a trait is an
  adaptation
• Not every adaptation is perfect. Long necks may
  confer an advantage in terms of mating success,
  but also make it difficult to get a drink!!

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Three methods for studying adaptation

• Experimental
• Observational
• Comparative

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Experimental

• Most powerful tool for testing hypotheses
• A good experiment restricts differences between
  study groups to one variable
• The tephritid fly has an unusual banding pattern
  on its wings. When threatened, they hold the
  wings perpendicular to their body
• This looks very similar to a fierce predatorthe
  jumping spider
• It was thought that they use this display to
  deter all types of predators
• However, they could be deterring only the jumping
  spider (one of their main predators) with this
  look-alike threat!

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Three hypotheses to test

• Hyp 1 The wings and display do not mimic
  spiders, perhaps they are only used as courtship
  displays?
• Hyp 2 They deter all types of predators that
  would fear the bite of a jumping spiderall types
  of insects, lizards etc.
• Hyp 3. They specifically deter jumping spiders
  by mimicking their threat!

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How to test?
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Predicted results
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Results
See considerations for quality experiments p.
338-339
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Observational studies

• Used when experimentation cannot be done cannot
  surgically alter the necks of giraffes
• May not be valid to bring species in an unnatural
  experimental setting when you want to determine
  how they behave in nature
• Behavioral regulation in ectothermic
  vertebratessnakes
• Garter snakes prefer a temperature between 28-32C
  in the lab
• How do they maintain this temperature in the
  wild, when the temperature constantly change
• Do they behaviorally thermoregulate? If so, how?

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Iguana thermoregulatory activity
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Garter snakes
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Hypotheses

• They can stay under rocks, however thick rocks
  never get warm, and thin rocks get too warm and
  could kill the snake
• They could remain on the surface and shuttle
  between temperatures, but would get dangerously
  cold at night
• They could remain in burrows, but may also get
  too cold as well

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Most found here
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Comparative method

• Compare among characters and predictions
• Why do some bats have larger testes than others?
• Sperm competition
• Usually occurs in large social groups

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Problem with previous graph, it does not account
for phylogenetic effect
Six species, however, what if many are related,
would that mean that they simply inherited large
group sizes and didnt evolve it independently?

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Not a valuable graph
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Must correct for this phylogenetic effect using
independent contrasts
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Independent contrasts for bats