Evolution Lecture 4: Natural Selection

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Evolution Lecture 4 Natural Selection
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Pattern and Process

• Living things appear related, modified, and
  obviously not independently created. How did
  this happen?
• Process Natural Selection

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Artificial Selection

• Darwin became a pigeon breeder and selected for
  desirable traits
• Cauliflower and broccoli are all varieties of
  cabbage. All the same species, artificially
  selected. Variation in the inflorescence
• Cauliflower gene encodes 254 aa that binds to DNA
  and activates the transcription of other genes.
• Apetala1 gene does the same thing as the
  CAULIFLOWER gene. There are there are two
  CAULIFLOWER alleles (Kent-2 and CAULIFLOWER).
• Lets examine the phenotypes

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CAULIFLOWER gene and artificial selection

• CAULIFLOWER gene has mutation aa 151, GAG to TAG.
  What happens?
• This loss of function causes bizarre
  inflorescence development
• It is hypothesized that farmers selected for
  individuals with these inflorescences (and the
  loss-of-function genes) over the years
• 2/11 alleles in cabbage
• 3/7 alleles in kale
• 8/9 alleles in broccoli
• 10/10 alleles in cauliflower

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Evolution by Natural Selection

• Variability within individuals
• Variation is heritable
• Some individuals are more successful at survival
• Survival and reproduction are not random.
  Individuals with the most favorable variations,
  those that are better at surviving and
  reproducing, are naturally selected.

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Fitness

• How well individuals survive and reproduce
• This term is relative. Fitness can only be
  compared to other individuals

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Adaptation

• Characteristic that increases the fitness of an
  individual compared to individuals without that
  trait.
• Behavioral or morphological adaptationsexploiting
  new resources or access to mates or higher
  reproduction.

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All four tenants of Natural Selection are testable

• Example The evolution of flower color in an
  experimental snapdragon population
• Jones and Reithal (2001) wanted to see if
  selection by bumblebees could influence the
  evolution of floral traits controlled by two
  alleles of a single gene.

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1)Variation in Population?2) Is it Heritable?
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3) Do individuals vary in their success at
surviving and reproduction?
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4) Is reproduction non-random?

• White plants with yellow spots appear as landing
  guides for bees. Therefore, those with more bee
  visitations produced more offspring. Also, white
  plants produce more seeds (fecundity).
• Did these populations evolve?

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Evolution
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Evolution in Natural Populations

• Evolution of Finches in the Galapagos14 species
  with huge variation in beak size
• Lets look at one species, the medium ground
  finch (Geospiza fortis), on the small island of
  Daphne Major.
• The finches do not migrate off of the island and
  virtually 100 of the population can be marked
  and studied
• It is known that the size of the beak is
  correlated with the size of the seeds harvested.
  Bigger birds eat bigger seeds and vice versa.
• Grant and Grant wanted to study the evolution of
  beak size in this population

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1) Variation?
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2) Heritability?
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Measuring heritability?

• Proportion of the variation observed in a
  population that is due to variation in genes.
• HVg/VgVe
• Therefore heritability ranges from 0-1
• Problems with measuring
• Misidentified paternity
• Conspecific nest parasitism
• Shared environments
• Maternal effects

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3) Variability in Success at Surviving and
Reproduction
Drought!
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84 of birds died
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4) Survival and reproduction non-random?
1. Only birds with large beaks could open the
large nuts 2. Large beaks and bodies are
correlated
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Did the population evolve?
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Over 30 years
Smaller beaks are Better in non-drought
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Must Remember

• Evolution is a statistical process of changing
  frequencies
• Natural Selection acts on individuals, but the
  consequence is on population
• Natural selection acts on phenotypes, but
  evolution consists of changes in allele
  frequencies
• Natural selection is not forward thinking