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Division Ave. High School
Ms. Foglia
AP Biology
Individuals are selected
Populations evolve
Chapter 23- Evolution of populations
Chapter 24Origin of species
Blue edged slides taken from slide shows by: Kim Foglia
http://www.explorebiology.com
REZNICK & ENGLER- (1980’s)
Guppy experiments
IMAGE FROM Campbell and Reece AP BIOLOGY
AP Biology
2007-2008
Small killifish eat juvenile guppies
Large pike-cichlids eat adult guppies
Guppies in populations with pike-cichlid predators
begin reproducing at a younger age and are smaller
at maturity than guppies in populations preyed on by
killifish
IMAGE FROM Campbell and Reece AP BIOLOGY
Changes in populations happened within 11 years
Age and size at sexual maturity change
depending on predators
Moving guppies to pools with different
predators changes size and age of maturity
in population
IMAGE FROM Campbell and Reece AP BIOLOGY
Changes in populations
Pesticide
molecule
Resistant
target site
Target site
Insect cell
membrane
Target site
Decreased number of target sites
Changes are heritable
Insecticide resistance
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2005-2006
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Division Ave. High School
Ms. Foglia
AP Biology
Body size & egg laying in water striders
Fitness
Variation & natural selection
Variation is the raw material for natural
Survival & Reproductive
selection
success
individuals with one
phenotype leave more
surviving offspring
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Where does Variation come from?
5 Agents of evolutionary change
Mutation
1977
Sex
Gene Flow
Non-random mating
Dry year
Dry year
environmental damage
Dry year
1980
1982
1984
mixing of alleles
Beak depth of
offspring (mm)
11
recombination of alleles
new arrangements in every offspring
new combinations = new phenotypes
some individuals must be more fit than others
Wet year
Beak depth
random changes to DNA
errors in mitosis & meiosis
there have to be differences within population
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Mutation
10
9
Genetic Drift
Medium ground finch
8
Selection
8
9
10
11
Mean beak depth of parents (mm)
spreads variation
offspring inherit traits from parent
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1. Mutation & Variation
Mutation creates variation
new mutations are constantly appearing
Mutation changes DNA sequence
changes amino acid sequence?
changes protein?
2. Gene Flow
Movement of individuals &
alleles in & out of populations
seed & pollen distribution by
wind & insect
migration of animals
sub-populations may have
changes structure?
different allele frequencies
changes function?
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causes genetic mixing
changes in protein may
change phenotype &
therefore change fitness
across regions
reduce differences
between populations
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Division Ave. High School
Ms. Foglia
AP Biology
Human evolution today
Gene flow in human
3. Non-random mating
Sexual selection
populations is
increasing today
transferring alleles
between populations
Are we moving towards a blended world?
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Image from: http://www.kittens-lair.net/store/en/articles/sylvester4.jpg
SEXUAL SELECTION
Favors traits with no advantage for survival
other than fact that males/females prefer them
Leads to pronounced differences between sexes
=SEXUAL DIMORPHISM
http://informalfotos.com/Fauna/Male%20Peacock%20displaying.JPG
http://www.distinctivecruises.com/AfricanSafaris/MaleFemaleLion.jpg
http://espanol.wunderground.com/data/wximagenew/i/icmoore/1013.jpg
4. Genetic drift
Effect of chance events
founder effect
small group splinters off & starts a new colony
bottleneck
some factor (disaster) reduces population to
small number & then population recovers &
expands again
KIN SELECTION
Natural selection that favors altruistic
behavior by enhancing reproductive
success of relatives
Bird that calls to warn others is in danger of being eaten,
but does it anyway.
Founder effect
When a new population is started
by only a few individuals
some rare alleles may be at high
frequency; others may
be missing
skew the gene pool of
new population
human populations that
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started from small group
of colonists
example:
colonization of New World
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Division Ave. High School
Ms. Foglia
AP Biology
Bottleneck effect
When large population is drastically
Cheetahs
All cheetahs share a small number of alleles
reduced by a disaster
famine, natural disaster, loss of habitat…
loss of variation by chance event
less than 1% diversity
as if all cheetahs are
identical twins
2 bottlenecks
alleles lost from gene pool
not due to fitness
narrows the gene pool
10,000 years ago
last 100 years
Ice Age
poaching & loss of habitat
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Conservation issues
Bottlenecking is an important
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Peregrine Falcon
concept in conservation
biology of endangered
species
5. Natural selection
Differential survival & reproduction due
to changing environmental conditions
climate change
food source availability
predators, parasites, diseases
loss of alleles from gene pool
reduces variation
reduces adaptability
toxins
combinations of alleles
that provide “fitness”
increase in the population
adaptive evolutionary change
Breeding programs must
consciously
outcross
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Golden Lion
Tamarin
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Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
POLYGENIC traits are controlled by
two or more genes.
DIRECTIONAL SELECTION
KEY
Food becomes scarce.
Low mortality,
high fitness
High mortality,
low fitness
A bell shaped curve is
typical of polygenic traits
Individuals at one end of the curve have higher
fitness than individuals in middle or at other end.
Graph shifts as some individuals fail to survive
at one end and succeed and reproduce at other
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
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Division Ave. High School
Ms. Foglia
AP Biology
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
EXAMPLE OF DIRECTIONAL SELECTION
Beak size varies in a population
STABILIZING SELECTION
Birds with bigger beaks can feed
more easily on harder, thicker
shelled seeds.
A food shortage causes small and
medium size seeds to run low.
Birds with bigger beaks would be
selected for and increase in numbers
in population.
http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg
STABILIZING SELECTION
Section 16-2
Male birds use
their plumage to
attract mates.
Male birds with
less brilliant and
showy plumage
are less likely to
attract a mate
Male birds with
showy plumage
are more likely to
attract a mate.
Stabilizing Selection
Key
Low mortality,
high fitness
High mortality,
low fitness
Selection
against both
extremes keep
curve narrow
and in same
place.
Brightness of
Male birds with
showier, brightly
colored plumage
also attract
predators, and
are less likely to
live long enough to
find a mate.
Individuals in center of the curve have higher
fitness than individuals at either end
Graph stays in same place but narrows as
more organisms in middle are produced.
EXAMPLE OF STABILIZING SELECTION
Human babies born with low birth
weight are less likely to survive.
Babies born too large have difficulty
being born.
Average size babies are selected for.
The most
fit is male
bird in the
middle-showy, but not
too showy.
Feather Color
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
DISRUPTIVE SELECTION
EXAMPLE OF DISRUPTIVE SELECTION
A bird population lives in area
where climate change causes medium
size seeds become scarce while large
and small seeds are still plentiful.
Individuals at extremes of the curve
have higher fitness than individuals in middle.
Birds with bigger or smaller beaks
would have greater fitness and the
population may split into TWO
GROUPS. One that eats small
seeds and one that eats large seeds.
Can cause graph to split into two.
Selection creates two DIFFERENT PHENOTYPES
http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg
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Division Ave. High School
Ms. Foglia
AP Biology
WHAT IS A SPECIES?
• Defined by Ernst Mayr
• Population whose members can interbreed
AND produce viable, fertile offspring
TWO DISTINCT SPECIES
Body and coloration are similar . . .
but their songs and other behaviors are different enough
to prevent interbreeding
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In the wild lions and tigers don’t interbreed
but in zoos… can get hybrids
LIGER - Male lion X female tiger
TIGON- Male tiger X female lion
Largest cat in world
. . . but male ligers are sterile
http://www.readthesmiths.com/articles/Images/Humor/Liger.jpg
http://laweekly.blogs.com/joshuah_bearman/images/tigon.jpg
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Blue Footed Booby dance
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Division Ave. High School
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Hybrid
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(DIVERGENT EVOLUTION)
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CURRENT DEBATE
NOT over whether evolution happens
… overwhelming evidence here!
BUT . . .Does speciation happen gradually
OR rapidly in response to environmental change?
GRADUALISM
Change happens slowly
“Baby steps” over long
Periods of time
CHARLES DARWIN
CHARLES LYELL
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Division Ave. High School
Ms. Foglia
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PUNCTUATED EQUILIBRIUM
Niles Eldredge- Curator
American Museum of Natural History
TIME
Rate of speciation is NOT CONSTANT
Stephen Jay Gould (1941-2002)
Paleontologist/evolutionary biologist
Rapid change when 1st split from parent
population
Unchanging for long periods
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