Evolution

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Evolution Speciation
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Evolution

• Evolution is the change in living things over
  long periods of time.
• It may occur through the processes of natural
  selection and genetic drift.

3
Natural Selection

• Natural selection explains why organisms are
  adapted to their environment.
• This theory describes a natural process that can
  produce new adaptations and new species.

4
Natural Selection

• 4 conditions
• Reproduction
• Variation in traits between individuals
• Heredity ? some of this variation must be
  heritable (genetic)
• Individuals differ in fitness (the number of
  offspring they produce) ? some individuals are
  more likely to reproduce than others

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Natural Selection

• If these 4 conditions are met, then natural
  selection will result.
• Lets look at an example

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Natural Selection

• A cryptic moth
• These moths reproduce
• There is variation in their wing color pattern
• This color pattern variation is heritable
  (offspring resemble their parents)

http//www.bio.umass.edu/biology/kunkel/catocala.h
tml
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Natural Selection

• 4. Because they use their color pattern as
  camouflage from bird predators, if individuals do
  not match their background they will get eaten ?
  only moths that look cryptic will survive and
  reproduce

http//www.bio.umass.edu/biology/kunkel/catocala.h
tml
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Natural Selection

• Other examples
• Pesticide resistant insects
• - only those that can tolerate the pesticide
  will survive and reproduce
• - if this pesticide tolerance is heritable, then
  their offspring will also be tolerant to the
  pesticide
• e.g. DDT used to be a very effective pesticide
  and initially wiped out 90 of mosquitoes in
  India.
• After about 10years, mosquitoes evolved
  resistance to DDT and now only 20 of
  mosquitoes are wiped out by DDT.

pesticide
Pesticide resistant insects
Surviving insects
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Natural Selection

• Other examples
• Antibiotic resistant bacteria
• - only those that can tolerate the antibiotic
  will survive and reproduce
• - if this antibiotic tolerance is heritable,
  then their offspring will also be tolerant to the
  antibiotic
• - have become increasingly prevalent as the use
  of antibiotics has become widespread
• e.g. About 70 of bacteria that cause infections
  in hospitals are resistant to at least one of the
  drugs most commonly used to treat infections.

Add antibiotic
Surviving bacteria
Antibiotic resistant strains
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Natural Selection

• Types of selection
• Directional selection
• Favors one extreme and shifts the population mean
• Stabilizing selection
• Favors the mean and decreases variation around
  the mean
• Disruptive selection
• Favors the extremes and selects against the mean

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Responses to Selection
of individuals
Coloration light dark
Directional selection
of individuals
Coloration light dark
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Responses to Selection
of individuals
Directional selection
Stabilizing selection
of individuals
Coloration light dark
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Responses to Selection
of individuals
Directional selection
Stabilizing selection
Disruptive selection
of individuals
Coloration light dark
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Genetic Drift

• Genetic drift is the fluctuation of genotypes in
  the population due to chance.
• In small populations, genetic drift can result in
  non-adaptive evolution.

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Genetic Drift
Genotype A
Genotype B
Population 2 61
Population 4 16
Population 1 11
For the population as a whole, the frequency of
the 2 genotypes is 11
Population 3 11
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Genetic Drift
Genotype A
Genotype B
Population 2 61
Population 4 16
Population 1 11
For the population as a whole, the frequency of
the 2 genotypes is 61 ? the frequency of
genotype A has increased due to chance
Population 3 11
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Genetic Drift
Genotype A
Genotype B
Population 2 61
Population 4 16
Population 1 11
For the population as a whole, the frequency of
the 2 genotypes is 11 ? the frequency of the 2
genotypes has remained the same due to chance
Population 3 11
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Genetic Drift

• Endangered species are often reduced to
  dangerously small numbers and restricted to
  small, isolated habitats.
• In small populations, genetic drift erodes
  genetic variation which limits a species ability
  to adapt to environmental change (e.g. disease,
  global warming, etc) and increases its
  probability of going extinct due to chance
  events.

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Speciation

• What is a species?
• A group of interbreeding individuals of common
  ancestry that are reproductively isolated from
  other groups

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Speciation

• How might speciation (formation of new species)
  occur?
• Allopatric speciation
• A barrier divides a continuous population into 2
  parts
• Parapatric speciation
• A hybrid zone divides a continuous population
  into 2 connected parts
• Sympatric speciation
• A population splits in 2 without any geographic
  separation

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Speciation
Ancestral population
A physical barrier divides the ancestral
population. Over time, each isolated population
diverges due to natural selection or drift
Allopatric speciation
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Speciation
Ancestral population
A physical barrier divides the ancestral
population. Over time, each isolated population
diverges due to natural selection or drift
There is some kind of habitat gradient that
results in locally adapted individuals.
hybrid zone
Parapatric speciation
Allopatric speciation
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Speciation
Ancestral population
The extremes in the population are selected for
and there is assortative mating.
A physical barrier divides the ancestral
population. Over time, each isolated population
diverges due to natural selection or drift
There is some kind of habitat gradient that
results in locally adapted individuals.
hybrid zone
Parapatric speciation
Sympatric speciation
Allopatric speciation
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Allopatric Speciation
Blue-headed wrasse
Isthmus of Panama
Cortez rainbow wrasse
http//cas.bellarmine.edu/tietjen/images/speciatio
n.htm
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Parapatric Speciation
http//cas.bellarmine.edu/tietjen/images/speciatio
n.htm
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Sympatric Speciation
Is thought to have occurred in Cichlids in a lake
in Central America (also in Africa).
http//www.cichlidnewsmagazine.com/issues/2001apr/
nicaragua.html
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The diversity of the animals we see today is the
result of processes such as natural selection and
genetic drift that lead to speciation over time.
Hawaiian honey-creepers