Download Cacti are adapted to their environment Polar bears are adapted to

Nothing in biology makes sense except in light of evolution.
– Theodosius Dobzhansky (1973)
Cacti are adapted to
their environment
Polar bears are adapted to their environment
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Wild orchids mimic female wasps
When we say that organisms are adapted to their environment...
what does this really mean?
A worthy definition of adaptation
Any heritable morphological, behavioral, or physiological trait that evolved th
through natural selection and increases h t l l ti
di
an organism's fitness under a given set of prevailing environmental conditions.
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Natural selection is the primary mechanism of evolution
Differential survival and reproduction of individuals (genotypes) in a population
individuals (genotypes) in a population
eliminates maladaptive alleles
(via individuals)
Darwin developed four postulates that if true would necessarily result in natural selection
If organisms vary;
If some of this variability is heritable;
If organisms produce more offspring than survive and;
If some survivors are better suited to the environment than others;
Individuals in a population vary and much of this variation is heritable
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What causes variation among individuals in a population?
Phenotypic variation
Genes
Environment
Genotypic variation
Phenotypic plasticity
Variation in the stature of coyote brush is due to phenotypic plasticity
Maritime
Inland
environment
not genetic
prostrate
upright
Krummholz growth
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Organisms produce more offspring than survive
...some survivors are better suited to the environment than others
Then…
Favorable traits will become more common in a population over successive generations
This is evolution by natural selection!
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Under “constant” conditions, stabilizing selection removes extreme alleles
Frequency of phe
enotype
in the population
Under changing conditions, directional selection is toward a new optimum
The peppered moth: directional selection in the field
Pre‐industrial era trees with lichens
Industrial era trees without lichens & covered in soot
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In disruptive selection, extreme traits are selected for
Frequency of phe
enotype
in the population
Black‐bellied seedcrackers
Case Study: phenotypic variation in Yarrow
Yarrow varies across a broad elevation gradient: what is the source of this variation?
Clausen, Keck and Hiesey (1940)
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To test this, CKH conducted a reciprocal transplant experiment
Ramets (genetic clones) from each location used to control for genotypic variation
Each set of ramets grown at each location
g
Stanford
(100 ft)
Mather
(4,550 ft)
Timberline
(9,900 ft)
Based on their results, what was the source of variation in the CKH study?
Phenotypic variation
Lo
ocations
Both genetic and environmental
Found ecotypes
Stanford
Mather
Timberline
Plant origin
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