Blue edged slides taken from slide shows by: Kim Foglia http://www.explorebiology.com
Chapter 23- Evolution of populations
Chapter 24- Origin of species
AP Biology 2007-2008
Populations evolveIndividuals are selected
REZNICK & ENGLER- (1980’s)Guppy experiments
Changes in populations happened within 11 years
Age and size at sexual maturity change depending on predators
IMAGE FROM Campbell and Reece AP BIOLOGY
Small killifish eat juvenile guppies Large pike-cichlids eat adult guppies
Guppies in populations with pike-cichlid predatorsbegin reproducing at a younger age and are
smallerat maturity than guppies in populations preyed
on bykillifish
IMAGE FROM Campbell and Reece AP BIOLOGY
Moving guppies to pools with different predators changes size and age of maturity in population
Changes are heritable
IMAGE FROM Campbell and Reece AP BIOLOGY
AP Biology 2005-2006
Changes in populationsPesticidemolecule
Insect cellmembrane
Target site
Resistanttarget site
Insecticide resistance
Target site
Decreased number of target sites
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Fitness Survival & Reproductive
success individuals with one
phenotype leave more surviving offspring
Body size & egg laying in water striders
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Variation & natural selection Variation is the raw material for natural
selection there have to be differences within population some individuals must be more fit than others
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Mean beak depth of parents (mm)
Medium ground finch8
8 9 10 11
9
10
11
1977 1980 1982 1984
Dry yearDry year
Dry year
Wet year
Bea
k d
epth
Bea
k d
epth
of
off
spri
ng
(m
m)
Where does Variation come from? Mutation
random changes to DNA errors in mitosis & meiosis environmental damage
Sex mixing of alleles
recombination of alleles new arrangements in every offspring
new combinations = new phenotypes spreads variation
offspring inherit traits from parent
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5 Agents of evolutionary changeMutation Gene Flow
Genetic Drift Selection
Non-random mating
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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?
changes structure? changes function?
changes in protein may change phenotype & therefore change fitness
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2. Gene Flow Movement of individuals &
alleles in & out of populations seed & pollen distribution by
wind & insect migration of animals
sub-populations may have different allele frequencies
causes genetic mixing across regions
reduce differences between populations
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Human evolution today Gene flow in human
populations is increasing today transferring alleles
between populations
Are we moving towards a blended world?Are we moving towards a blended world?
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3. Non-random mating Sexual selection
SEXUAL SELECTIONFavors 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.JPGhttp://www.distinctivecruises.com/AfricanSafaris/MaleFemaleLion.jpghttp://espanol.wunderground.com/data/wximagenew/i/icmoore/1013.jpg
KIN SELECTIONNatural 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.
Image from: http://www.kittens-lair.net/store/en/articles/sylvester4.jpg
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Warbler
finch
Tree
finc
hes
Ground finches
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
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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
started from small group of colonists
example: colonization of New World
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Bottleneck effect When large population is drastically
reduced by a disaster famine, natural disaster, loss of habitat… loss of variation by chance event
alleles lost from gene pool not due to fitness
narrows the gene pool
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Cheetahs All cheetahs share a small number of alleles
less than 1% diversity as if all cheetahs are
identical twins
2 bottlenecks 10,000 years ago
Ice Age last 100 years
poaching & loss of habitat
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Conservation issues Bottlenecking is an important
concept in conservation biology of endangered species loss of alleles from gene pool reduces variation reduces adaptability
Breeding programs must consciously outcrossBreeding programs must consciously outcross
Peregrine Falcon
Golden Lion Tamarin
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5. Natural selection Differential survival & reproduction due
to changing environmental conditions climate change food source availability predators, parasites, diseases toxins
combinations of alleles that provide “fitness” increase in the population adaptive evolutionary change
POLYGENIC traits are controlled by two or more genes.
A bell shaped curve is typical of polygenic traits
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
DIRECTIONAL SELECTIONGraph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
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
Low mortality, high fitness
High mortality, low fitness
KEY
Food becomes scarce.
Beak size varies in a population
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.
EXAMPLE OF DIRECTIONAL SELECTION
http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg
STABILIZING SELECTIONGraph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
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.
Key
Per
cen
tag
e o
f P
op
ula
tio
n
Brightness of
Feather Color
Selection against both
extremes keep curve narrow and in same
place.
Section 16-2
Low mortality, high fitness
High mortality, low fitness
Stabilizing SelectionMale 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.
Male birds withshowier, brightlycolored plumagealso attractpredators, and are less likely to live long enough tofind a mate.
The mostfit is malebird in the middle--showy, but not too showy.
STABILIZING SELECTION
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
Human babies born with low birth weight are less likely to survive.
Babies born too large have difficultybeing born.
Average size babies are selected for.
EXAMPLE OF STABILIZING SELECTION
DISRUPTIVE SELECTIONGraph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
Individuals at extremes of the curve have higher fitness than individuals in middle.
Can cause graph to split into two. Selection creates two DIFFERENT PHENOTYPES
A bird population lives in area where climate change causes medium size seeds become scarce while large and small seeds are still plentiful.
Birds with bigger or smaller beaks would have greater fitness and thepopulation may split into TWO GROUPS. One that eats small seeds and one that eats large seeds.
EXAMPLE OF DISRUPTIVE SELECTION
http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg
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
In the wild lions and tigers don’t interbreedbut in zoos… can get hybrids
LIGER - Male lion X female tigerTIGON- Male tiger X female lion
Largest cat in world . . . but male ligers are sterile
http://www.readthesmiths.com/articles/Images/Humor/Liger.jpghttp://laweekly.blogs.com/joshuah_bearman/images/tigon.jpg
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Blue Footed Booby dance
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Hybrid
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(DIVERGENT EVOLUTION)
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CURRENT DEBATENOT 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 longPeriods of time
CHARLES DARWINCHARLES LYELL
PUNCTUATED EQUILIBRIUM
Niles Eldredge- Curator American Museum of Natural History
Rate of speciation is NOT CONSTANT
Rapid change when 1st split from parent population
Unchanging for long periods
Stephen Jay Gould (1941-2002) Paleontologist/evolutionary biologist
TIME
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