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

2. Individuals are selected
Populations evolve

3. REZNICK & ENGLER- (1980’s) Guppy experiments
IMAGE FROM Campbell and Reece AP BIOLOGY
Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field
Changes in populations happened within 11 years
Age and size at sexual maturity change
depending on predators

4. IMAGE FROM Campbell and Reece AP BIOLOGY
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

5. 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

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

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

8. 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

9. 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)

10. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

11. 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.

12. A diverse gene pool is important for the survival of a species in a changing environment
Environments can more stable, less stable or fluctuating
This affects evolutionary rate and direction
Different genetic variations can be selected in each different generation

13. 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

14. 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?

15. 3. Non-random mating
Sexual selection

16. 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

17. 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 others is in danger of being eaten, but does it anyway.

18. 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

19. Reduction of genetic variation within a given population can increase the differences between populations of the same species.

20. 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!)

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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.

28. 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.

29. 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

30. 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.

31. 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

32. 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.