1. Chapter 23- Evolution of populations
Blue edged slides taken from slide shows by: Kim Foglia

2. Presence of lactate dehydrogenase
Populations evolve
Natural selection acts on individuals
differential survival
“survival of the fittest”
differential reproductive success
who bears more offspring
Populations evolve
genetic makeup of population changes over time
favorable traits (greater fitness) become more common
Presence of lactate dehydrogenase
The Mummichog (Fundulus heteroclitus heteroclitus) is a small killifish found in the eastern United States. It is capable of tolerating highly variable salinity and temperatures, and is found in estuaries and saltmarshes as well as less salty waters.
A year-round resident of tidal creeks and wetlands, this brownish-green saltwater minnow may reach a maximum length of 5 inches. Its Indian name means "they go in great numbers." It is also known as the common killifish.
A hardy fish, the mummichog is an important food source for larger fish and is often used as bait. The mummichog also has been used as a natural method of mosquito control in marsh ponds and ditches. It has been reported that one mummichog can eat as many as 2,000 mosquito larvae ("wrigglers") a day. The mummichog also feeds on other insects, small fish, crustaceans, and plant material.
Because of the extreme hardiness of the species, it is sometimes the only species found in severely polluted and oxygen-deprived streams, such as the Hackensack River and the Arthur Kill in New Jersey during the height of the water pollution problem in the United States. In 1973 the Mummichog became the first fish in space when carried on Skylab 3 as part of the biological experiments package later space missions by the U.S., such as Bion 3, have also carried Mummichog.
Mummichog

3. Changes in populations
Bent Grass on toxic mine site
Pocket Mice in desert lava flows
Pesticide molecule
Insect cell membrane
Target site
Resistant target site
Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field
Target site
Decreased number of target sites
Insecticide resistance

4. Individuals DON’T evolve…
Individuals survive or don’t survive…
Individuals DON’T evolve…
Individuals are selected
Populations evolve
Individuals reproduce or don’t…

5. Fitness Survival & Reproductive success
Body size & egg laying in water striders
Fitness
Survival & Reproductive success
individuals with one phenotype leave more surviving offspring

6. 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

7. 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
Mean beak depth of parents (mm)
Medium ground finch 8 9 10 11
1977
1980
1982
1984
Dry year
Wet year
Beak depth
Beak depth of
offspring (mm)

8. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

9. Not every mutation has a visible effect.
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
Every individual has hundreds of mutations
1 in 100,000 bases copied
3 billion bases in human genome
But most happen in introns, spacers, junk of various kind
Not every mutation has a visible effect.
Some effects on subtle.
May just affect rate of expression of a gene.

10. 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

11. Are we moving towards a blended world?
Human evolution today
Gene flow in human populations is increasing today
transferring alleles between populations
Are we moving towards a blended world?

12. 3. Non-random mating
Sexual selection

13. 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

14. Image from: http://www. kittens-lair. net/store/en/articles/sylvester4
KIN SELECTION
Natural selection that favors altruistic behavior by enhancing reproductive success of relatives
Bird that calls to warn when others is in danger of
being eaten,

15. 4. Genetic drift Effect of chance events founder effect bottleneck
small group splinters off & starts a new colony
bottleneck
some factor (disaster) reduces population to small number & then population recovers & expands again
1 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families
Genghis Khan tracked through Y chromosome.
Warbler
finch
Tree finches
Ground finches

16. 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
Small founder group, less genetic diversity than Africans
All white people around the world are descended from a small group of ancestors
100,000 years ago
(Chinese are white people!)

17. 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

18. Cheetahs All cheetahs share a small number of alleles 2 bottlenecks
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

19. Peregrine Falcon
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 outcross
Golden Lion Tamarin

20. 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

21. typical of polygenic traits
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

22. DIRECTIONAL SELECTION
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
DIRECTIONAL SELECTION
KEY
Low mortality,
high fitness
High mortality,
low fitness
Food becomes scarce.
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

23. EXAMPLE OF DIRECTIONAL SELECTION
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.

24. STABILIZING SELECTION
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
STABILIZING SELECTION
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.

25. STABILIZING SELECTION
Section 16-2
Male birds with
showier, brightly
colored plumage
also attract
predators, and are less likely to live long enough to
find a mate.
The most
fit is male
bird in the middle--
showy, but not too showy.
Stabilizing Selection
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.
Key
Low mortality, high fitness
High mortality, low fitness
Selection against both extremes keep curve narrow and in same place.
Percentage of Population
Brightness of
Feather Color
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006

26. 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.

27. DISRUPTIVE SELECTION Individuals at extremes of the curve
Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
DISRUPTIVE SELECTION
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

28. 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.
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.