Chapter 10 Studying Adaptation

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Chapter 10 Studying Adaptation

• Evolutionary Analysis of Form and Function

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Adaptation

• An adaptive trait or suite of traits that
  increases an organisms fitness
• Clayton et al., 2005

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Testing adaptive significance

• Demonstrate the function of the trait
• Show that having the trait increases fitness
• Contributes more genes to the population
• BEWARE
• Conventional wisdom
• Being seduced by plausibility and charm

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Reconsider the Oxpecker
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Oxpecker effects on tick load
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Oxpeckers and maintenance of open wounds
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Oxpeckers and hosts earwax
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Conclusion?

• Oxpeckers are vampires
• Oxpeckers eat earwax
• When oxpeckers eat ticks they prefer female ticks
  engorged with blood
• On the oxen, the oxpeckers appear to be parasites

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Hypotheses must be tested

• Differences among populations or species are not
  always adaptive
• Not every trait is an adaptation
• Not every adaptation is perfect

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Methods for testing hypotheses

• Experiments
• Observations
• Comparative

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What is the function of the wing markings and
wing-waving display of the tephritid fly
Zonosemata?
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Starting question

• Do the wing markings and wing movements
  convincingly mimic the jumping spider territorial
  display so that it helps the flies to escape
  predation?

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Competing hypotheses

• The flies do not mimic jumping spiders
• The flies mimic jumping spiders to deter
  predators that fear jumping spiders
• The flies mimic jumping spiders to deter
  predation by jumping spiders

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Control and experimental groups
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Experimental design, cont

• What to measure? Number of responses
• Retreat
• Stalk and attack
• Kill
• How to induce the jumping spiders to act like
  predators?
• Starve them for 2 days

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Results
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Experimental design

• Define and test appropriate control groups
• Controls and experimentals must be treated
  exactly the same
• Randomization can control for miscellaneous
  effects
• Replications are important
• Reduce distortion by outliers
• Gives evidence of precision of experiment
• Allows use of statistical tests

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Precision and bias
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Observational studies
The effects of behavioral thermoregulation on
desert iguana physiology
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One way to test behavioral thermoregulation
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Thermoregulatory behavior in garter snakes

• Do garter snakes make adaptive choices when
  looking for a nighttime retreat?
• Ray Huey and colleagues (1989b) implanted
  miniature radio transmitters that reported
  location and temperature.
• Preferred temperature was 28-32 C
• Thermoregulated by staying under rocks and moving
  up and down burrows.

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Body temperatures of garter snakes in nature
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Temperatures under a rock
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Temperatures in a burrow
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Distribution of rocks at Eagle Lake, CA
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The comparative method

• Comparisons can be used to examine the evolution
  of form and function
• Why do some bats from the group Megachiroptera
  have bigger testes than other bats in that group?
• Hosken and colleagues (1998) hypothesized that
  testes size is an adaptation in sperm
  competition.
• Under what conditions would you have sperm
  competition?

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Variation in testis size vs. social group size
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Plot sister species
Hypothetical phylogeny
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Felsensteins method for evaluating
phylogenetically independent contrasts
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Correlated evolution of group size and testes
size in fruit bats and flying foxes
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Phenotypic plasticity

• Not all phenotypes have genetic origins
• The environment can affect phenotypes
• Are phenotypic plasticity effects adaptive?

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Daphnia
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Variation in phototactic behavior in D. magna
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Evolution of phototactic behavior in D. magna
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Dobzhansky

• Selection deals not with the genotype as such,
  but with its dynamic properties, its reaction
  norm, which is the sole criterion of fitness in
  the struggle for existence.

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Trade-offs flower size in begonias
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How do bees select on female flower size?

• Hypothesis 1 The closer a female mimics male
  flower characteristics the more bees will be
  attracted.
• Favors stabilizing selection
• Hypothesis 2 The closer a female mimics the most
  rewarding male characteristics (flower size), in
  the bees perspective, then the more bees will be
  attracted (to larger flowers).
• Favors directional selection

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Hypotheses
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Bee preference for flower size
Visit artificial flowers
Approach artificial flowers
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The trade off Number of female flowers per
inflorescence
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A constraint flower color change
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Fuchsia anatomy
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Fuschia physiology
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Why maintain red flowers?

• Red flowers attract pollinators to the tree.
• The red flowers represent a physiological
  constraint

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Fuschia physiology
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Flying pigs
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Host shifts
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Host shifts hypotheses

• All host shifts are genetically possible.
• Predators and competitors limit host selection
• Most host shifts are genetically impossible
• Host shifts are determined by what is genetically
  possible.
• Most species lack genetic variation in feeding
  mechanisms and detoxifying compounds to move to
  any host.

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Constraint by dispersal ability
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The parasitic hippoboscid fly
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Selection operates on different levels

• Selection can act at the level of organelles.
• Selection can act at the level of the cell
  despite strong selection against the allele at
  the individual level.

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Selection in yeast

• Mitochodria are used for respiration
• When mitochondria lose the ability respire they
  are considered parasites
• When yeast have parasitic mitochondria, they
  produce energy through fermentation

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Taylor and colleagues (2002)

• Established yeast populations with both normal
  and parasitic mitochondria
• Mitochondrial genomes that replicate rapidly will
  outcompete those that replicate more slowly.
• Parasitic genomes replicate more quickly
• Yeast cells favor respiration
• Selection at the level of the mitochondria
  opposes selection at the level of the yeast cell.

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Selection and yeast cells
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Mutations in human sperm
Apert syndrome
Crouzon syndrome
Nonsense mutation
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Strategies

• Study natural history. Learn about an organism
  in detail
• Question conventional wisdom
• Question assumptions
• Draw analogies. Questions explored in one taxon
  may apply to different taxons
• Examine trade-offs and constraints
• Question whether selection may be happening at a
  different level.