Cross-Dressing Salmon

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Cross-Dressing Salmon

• By Tom Horvath (adapted with changes by Julie
  Korb)
• SUNY College at Oneonta

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CQ1 Which statement best describes natural
selection?

1. Survival of the fittest.
2. The strongest individuals get to reproduce.
3. The best adapted individuals survive and
   reproduce.
4. Survival and reproduction is a matter of luck.

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http//www.youtube.com/watch?v5DqjsWsY8-g
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CQ2 Out of all the eggs a female lays, how many
hatchlings (or smolts) do you think will survive
to spawn?

1. 50 (50 out of 100)
2. 10 (10 out of 100)
3. 1 (1 out of 100)
4. 0.1 (1 out of 1000)
5. Less than 0.1

Mass of fertilized salmon eggs
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About 0.03 survive reproduce themselves
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Which are the lucky few who make it to reproduce?
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Charles Darwins Theory of Natural Selection
It is not just random luck. Some individuals
have a better chance of surviving and reproducing
than others.
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CQ3 Are all these smolts ABSOLUTELY
identical? A Yes B No
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Variation in salmon translates into variations in
survival and reproductive success.
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Theory of Evolutionby Natural Selection

• More offspring produced than survive to adulthood
  (OVERPRODUCTION).
• Variation among individuals of a species.

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What good is variation? Talk to your neighbor and
list as many characteristics a salmon may possess
that helps it survive.
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ADAPTATION

• Any characteristic that improves the survival or
  reproductive success of an organism.
• Often the result of natural selection.
• Organisms match closely with their environment.

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Survival is only half the story you have to
reproduce to pass on those good traits that aided
survival to this point.
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Theory of Evolutionby Natural Selection

• More offspring produced than survive to adulthood
  (OVERPRODUCTION).
• Inheritable variation among individuals of a
  species.
• Best adapted individuals survive and reproduce
  (UNEQUAL REPRODUCTIVE SUCCESS).

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Typical Dominant Male Phenotype
http//www.arkive.org/atlantic-salmon/salmo-salar/
video-09a.html?offset0pt
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• The most dominant males (usually largest and
  most aggressive) successfully defend their redds
  and inseminate the eggs. Smaller males that also
  have the kype lose out in head-to-head
  competition with larger males.
• CQ4 Are we seeing survival of the fittest in
  action here?
• A. Yes
• B. No

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A Different Type of Male Female Mimic

• Lack dominant male characteristics (e.g., no
  kype).
• Appear more female-like.
• Disadvantage They cant compete head-to-head
  with dominant males either, but.

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Why dont female mimics get weeded out through
natural selection if they are not fit?
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CQ5 Why are female mimics still found in each
generation?

• Some outcompete the dominant males in the redds.
• They appear from mutations randomly each
  generation.
• They have a different reproductive strategy from
  dominant males and it works.
• Some females change into males under stressful
  environmental conditions.

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Cross-Dressing Salmon
Female mimics can stay near the redds because
dominant males dont see them as competition
they think they are females. These fish get a
brief chance to inseminate a few eggs before
being ultimately bumped out by dominant males.
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• CQ6 Even though female mimics are not
  dominant, are they fit?
• A. Yes
• B. No

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Survival of the Fittest?
Darwinian fitness contribution an individual
makes to the gene pool of the next generation
relative to the contribution of others.
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Fitness can be compared with relative values
(values from 1 to 0)

• A fitness value of 1 is assigned to the phenotype
  with the highest representation.
• All other phenotypes are assigned based on their
  reproductive success relative to the dominant
  type.

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Fitness Value Example

• Dominant male phenotype produces 300 male
  offspring in the next generation.
• Female mimic phenotype produces 50 male offspring
  in the next generation.
• Small male phenotype produce only 5 male
  offspring.

Dominant Male Phenotype Fitness 300/300
1.0 Female Mimic Phenotype Fitness 50/300
0.17 Small Male Phenotype Fitness 5/300 0.02
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Natural Selection

• Analyzing change in frequency of traits in a
  population
• Three patterns emerge
• Directional selection
• Stabilizing selection
• Diversifying selection

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Natural Selection

• Directional Selection -Individuals of one
  extreme phenotype favored.

• Stabilizing Selection - Individuals with
  intermediate phenotype favored
• Extreme phenotypes selected against.

• Diversifying Selection - Both extreme phenotypes
  favored intermediate phenotypes selected
  against.

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Directional Selection
Individuals of one extreme phenotype favored
Population under directional selection
Population with no natural selection
Frequency
Body Size of Salmon
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Stabilizing Selection
Individuals with intermediate phenotype favored
extreme phenotypes selected against
Population under stabilizing selection
Population with no natural selection
Frequency
Body Size of Salmon
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Diversifying Selection
Both extreme phenotypes favored intermediate
phenotypes selected against
Population with no natural selection
Population under disruptive selection
Frequency
Body Size of Salmon
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CQ7 Given our fitness value from the example,
which pattern of selection would we expect in the
salmon population?

1. Directional selection
2. Stabilizing selection
3. Diversifying selection
4. Unnatural selection

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CQ8 Do individuals have to be the strongest
to be fit?

1. Yes
2. No

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CQ9 Which of these traits might confer fitness
upon an individual?

1. Being sneaky and tricking the dominant males into
   letting you hang around the spawning females.
2. Having an awesome hook on your jaw and large body
   size.
3. Having sperm that are extra good at finding and
   fertilizing eggs.
4. Being extra good at storing fat, which will fuel
   all that waterfall jumping while migrating
   upstream.
5. Any of the above will increase fitness.