Testing adaptive hypotheses: a case study

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Testing adaptive hypotheses a case study
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...the wild guppy
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Poecilia reticulata
Lives in gravel-bottomed forest streams
headwaters to lowlands
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Poecilia reticulata
Lives in gravel-bottomed forest streams
headwaters to lowlands
Great variation in coloration from population to
population, even within the same stream
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Poecilia reticulata
Lives in gravel-bottomed forest streams
headwaters to lowlands
Great variation in coloration from population to
population, even within the same stream
Lots of natural predators generally more and the
most ferocious are at lower elevations
(downstream)
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Poecilia reticulata
Lives in gravel-bottomed forest streams
headwaters to lowlands
Great variation in coloration from population to
population, even within the same stream
Up to 7 natural predators generally more and the
most ferocious are at lower elevations
(downstream)
Brightest guppy populations tend to live
upstream populations downstream are duller in
color
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Poecilia reticulata
Lives in gravel-bottomed forest streams
headwaters to lowlands
Great variation in coloration from population to
population, even within the same stream
Up to 7 natural predators generally more and the
most ferocious are at lower elevations
(downstream)
Brightest guppy populations tend to live
upstream populations downstream are duller in
color
Females are dull gray (and blend in with the
stream bed) in all populations
Females (always look like this)
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Forming an adaptive hypothesis about wild guppies
What are the necessary conditions for evolution
by natural selection?
1. variation
2. heritability offspring resemble parents
3. survival and reproduction are not random
consistent relationship between phenotype and
fitness
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Forming an adaptive hypothesis about wild guppies
What are the necessary conditions for evolution
by natural selection?
1. variation
2. heritability offspring resemble parents
3. SELECTION consistent relationship between
phenotype and survival and reproduction
What is an adaptation?
The phenotypic variant that results in the
highest fitness in a given environment
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You can
Move and remove guppies and predators from
streams Maintain and breed guppies in a
laboratory Cross guppies from different
populations Determine paternity/maternity of
individual guppies Genetically engineer and clone
guppies Spend years of your life on this project
(i.e. allow many, many guppy generations to
pass Anything else (within reason)
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Endlers experiments
The phenotype of each population is adapted, and
is the result of the local balance of sexual and
predator selection
If the balance of sexual and predator selection
is changed, the phenotype should evolve in
response
Environment-dependent
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Endlers experiments
Greenhouse pool experiment
Set up guppy populations in pools in a greenhouse
Foundation population highly variable
Sexual selection constant (always)
Vary predation pressure
Vary environment
Track phenotypes through time number, size,
location, color variation of spots
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Endlers results
innocuous predator
Ponds with no predators (K) showed a steady
increase in the of spots
control
voracious predator
Little change in spot (compared to the control)
after addition of the innocuous predator (R)
Pools that received a voracious predator
treatment (C) showed a marked decrease in the
of spots
Foundation population
Treatments applied
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Summary of greenhouse experiment
Phenotypes evolved in response to changes in the
balance of sexual and predation selection
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Endlers experiments 2. Field transplant in
Trinidad
Each population has an adapted phenotype,
reflecting the local balance of sexual and
predation selection.
If evolution was replayed, the same adapted
phenotype would evolve.
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Endlers experiments 2. Field transplant in
Trinidad
Each population has an adapted phenotype,
reflecting the local balance of sexual and
predation selection.
Trinidad stream 3 sites...
No guppies innocuous predator present
Transplanted 200 guppies from site 3 to site 1,
measured phenotypes 10 months later.
Population 1 should evolve the same phenotypes as
population 2 (site 1 site 2).
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Endlers field experiment results
In site 1 (x)....
Spot size, number and color diversity increased
Color pattern converged on that of fish in site 2
(r)
c site 3 (source pop), x site 1 (transplant
site), r site 2
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Endlers work Conclusions
Demonstration of natural selection in action
Evolutionary hypotheses are experimentally
testable