Transcript Beach Plants

EVOLUTION
Part 2
Evolution

Changes in gene pool over time
Evolution

Includes populations diverging from one
another over time
 may lead to new species
Mechanisms of Evolution

Genetic Drift
Population Bottlenecks
 Founder Effect


Gene Flow
Immigration
 Emigration



Mutations
Natural Selection
Genetic Drift

Changes in gene pool of populations due to
random chance
Genetic Drift
Genetic Drift
Image Credit: UC Museum of Paleontology's Understanding Evolution www.evolution.berkeley.edu
Genetic Drift

Genetic drift has a bigger effect on small
populations.
Bottleneck Effect

Changes in gene pool of populations due to
some event
 drastically reduces population
Bottleneck Effect


Survival is random
Whether an organism survives does not
depend on any characteristic (allele)
Example of Bottleneck Effect


Population of plants on
a mountain side
An avalanche wipes out
all but a patch of plants
behind the shelter of a
large outcrop.
Example of Bottleneck Effect


Plants behind the outcrop survived only
because they were out of the path of the
avalanche.
There was nothing about the plants’ genes that
influenced survival.
Example of Bottleneck Effect

Surviving population has an allele frequency
different from the original population.
Bottleneck Effect
Bottleneck Effect: Cheetahs



10,000 years ago,
cheetah populations
worldwide crashed
Due to climate
change
Photo Credit: Courtesy of Smithsonian National
Zoo @ nationalzoo.si.edu
Cheetahs



Only cheetahs
in Africa &
Eurasia
survived
Location, not
genes 
Survival
Photo Credit: Kevin Walsh, 2006,
Wikimedia Commons
Cheetahs

Cheetahs today: Genetically identical

Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons
Bottleneck Effect:
Northern Elephant Seals



Once numerous in
the northern Pacific.
1800s: Hunted
extensively for
blubber
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals


Only 100-1000
animals in a
Mexican colony
survived
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals
Today:
>100,000
individuals
 Very little
genetic
diversity


Photo Credit: Mila Zinkova, 2008,
courtesy of Wikimedia Commons
Founder Effect


New population established by very small
number of individuals (“founders”)
By chance, founder group has a different allele
mix than original population
Example of Founder Effect

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200 German
immigrants
founded the Old
Order Amish of
Pennsylvania
Photo credit: : Matthew Trump, 2004,
Wikimedia Commons
Old Order Amish


One couple
brought allele
polydactyly 
Six fingers and
toes
Photo credit: G. Baujat and M
LeMerrer, 2007, Wikimedia
Commons
Old Order Amish


Inbreeding has 
frequency of
polydactyly
Click on this link:
http://www.pbs.org/wgbh/evolution/library/
06/3/l_063_03.html

Photo credit: gadjoboy, 2006, Wikimedia
Commons
Gene Flow



Movement of alleles between populations
Immigration: movement of alleles into a
population
Emigration: movement of alleles out of
population
Example of Gene Flow


Transfer of pollen from
one population of
sunflowers into another
population of sunflowers
Photo Credit: Sunflower Pollen, Courtesy of
Wikimedia Commons
Example of Gene Flow

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
Male juvenile Belding’s
ground squirrels
emigrate from their
birthing population to
new populations.
40-70% emigrate as
juveniles. Remaining
males leave by the end
of their first year.
Photo Credit: Courtesy of Yathin at FlickR,
http://www.flickr.com/photos/yathin/807378578/in
/set-72157600812861150/
Mutations

Mutations can
add new alleles
to a population

Photo Credit for black Eastern Fox Squirrel: Jeffrey
Pippen, Duke University

Photo Credit for wild-type Eastern Fox Squirrel:
Calibas, 2007, Wikimedia Commons
Asexual Populations


Mutations are
primary source
of genetic
variation in
asexual
populations
Photo Credit for E. coli 0157 colonies: Centers
for Disease Control, 2005, Wikimedia
Commons
Natural Selection


Environment determines which genes are
passed onto the next generation
Based on which individuals successfully
survive and reproduce
Natural Selection

Requires:
 Genetic
Variation
 Overproduction of Offspring
 Struggle for Existence
 Differential Survival and Reproduction
View video at: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Photo credit: Dean E. Briggins, U.S. Fish and Wildlife Service, http://www.nsf.gov/news/news_images.jsp?cntn_id=104263&org=LPA
Genetic Variation


Organisms in the population vary in their
characteristics
Variations are heritable  Passed from parents
to offspring
Variation in Snail Shells
Flower Variations
Natural
Selection
Flow
Chart
How
Natural
Selection
Works
View “Pocket Mouse and Predation” at
http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: Cheryl S. Brehme, USGS at http://soundwaves.usgs.gov/2006/02/pubs.html
View “Pocket Mouse Evolution” at
http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: J. Harris, American Society of Mammalogy, at: http://www.mammalogy.org/mil_images/images/mid/752.jpgl
Artificial Selection


Humans select which genes are passed onto
the next generation
Based on characteristics that humans find
valuable or desirable
View “Dog Breeding” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: papillon.cz, courtesy of Wikimedia Commons (http://commons.wikimedia.org/wiki/Image:%21flowers.jpg)
View “Breeding Teosinte” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: USDA, 2005, courtesy of Wikimedia Commons
Another Example of Artificial Selection
Sexual Selection

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Some
characteristics
influence
individual’s
chance of
mating
Photo Credit: Ian Sewell, 2006,
Wikimedia Commons
Sexual Selection


Individual may
have shorter life
but will have
better chances
of mating and
producing
offspring
Photo Credit: David Dennis, 2007,
Wikimedia Commons
Types of Sexual Selection

Mate Competition
 One
sex competes for access to the other sex
 Other sex always “chooses” winner

Mate Choice
 One
sex chooses mate based on
characteristics of other sex
Example of Mate Competition


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Male bighorn
sheep fight for
mates
Male with largest
horns usually wins
Photo Credit: Alan D. Wilson,
naturespicsonline.com,
courtesy of Wikimedia
Commons
Video of Bighorn Sheep Fighting:
http://www.youtube.com/watch?v=WKmGiSm3-2U
Photo Credit: Jon Sullivan, Wikimedia Commons
Example of Mate Choice
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
Peacocks display
their tails
Females choose
male with
showiest tail
Photo credit: Aaron Logan,
www.lightmatter.net, courtesy of Wikimedia
Commons
Example of Mate Choice


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Large tails
decrease survival
of peacocks
Natural selection
favors small tails
Photo credit: Jörg Hempel, courtesy of
Wikimedia Commons
Example of Mate Choice


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Peacocks with
small tails do
not mate
Mate choice
favors large
tails
Photo credit: Jyshah, 2007, courtesy
of Wikimedia Commons
View the video at:
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
Photo credit: Myukii, courtesy of Wikimedia Commons
THE END
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.