8/7/2019 Selection (KFogler)

1/21

AP Biology 2007-2008

Evolutionary Forces

What changes populations?

8/7/2019 Selection (KFogler)

2/21

AP Biology

Forces of evolutionary change

Natural selection

traits that improve survival

or reproduction will accumulate

in the population adaptive change

Genetic drift

frequency of traits can change

in a population due to

chance events

random change

8/7/2019 Selection (KFogler)

3/21

AP Biology

Natural Selection

Selection acts on any trait that affectssurvival or reproduction

predation selection

physiological selection

sexual selection

8/7/2019 Selection (KFogler)

4/21

AP Biology

Predation Selection

Predation selection act on both predator & prey

behaviors

camouflage & mimicry

speed

defenses (physical & chemical)

8/7/2019 Selection (KFogler)

5/21

AP Biology

Physiological Selection

Acting on body functions

disease resistance

physiology efficiency (using oxygen, food, water)

biochemical versatility protection from injury

HOT STUFF!Some fish had the

variation of producinganti-freeze protein

5.5 mya5.5 mya

The Antarctic OceanThe Antarctic Ocean

freezes overfreezes over

8/7/2019 Selection (KFogler)

6/21

8/7/2019 Selection (KFogler)

7/21

8/7/2019 Selection (KFogler)

8/21

AP Biology

QuickTime and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Sexual selection

Its FEMALE CHOICE, baby!

8/7/2019 Selection (KFogler)

9/21

AP Biology

The lions mane

Females are attracted to

males with larger, darkmanes

Correlation with highertestosterone levels

better nutrition & health

more muscle & aggression

better sperm count / fertility

longer life

But imposes a cost to male HOT! Is it worth it??

8/7/2019 Selection (KFogler)

10/21

AP Biology

Sexy = fitness markers

8/7/2019 Selection (KFogler)

11/21

AP Biology

Sexual selection

Acts in all sexuallyreproducing species

the traits that get you mates

sexual dimorphism

influences both morphology &

behavior

can act in opposition to natural

selection

Jacanas

Is there a testable

hypothesis in there?

8/7/2019 Selection (KFogler)

12/21

AP Biology

Coevolution

Two or more species reciprocallyaffect each others evolution

predator-prey

disease & host

competitive species

mutualism

pollinators & flowers

8/7/2019 Selection (KFogler)

13/21

AP Biology

Effects of Selection

Changes in the average trait of a populationDIRECTIONAL

SELECTION

STABILIZING

SELECTION

DISRUPTIVE

SELECTION

giraffe neckhorse size human birth weight rock pocket mice

8/7/2019 Selection (KFogler)

14/21

8/7/2019 Selection (KFogler)

15/21

AP Biology

Founder effect

When a new population is startedby only a small group of individuals

just by chance some rare alleles may

be at high frequency;others may be missing

skew the gene pool of

new population

human populations thatstarted from small group

of colonists

example:

colonization of New Worldalbino deer Seneca Army Depot

8/7/2019 Selection (KFogler)

16/21

AP Biology

Distribution of blood types Distribution of the O type blood allele in native

populations of the world reflects original settlement

8/7/2019 Selection (KFogler)

17/21

8/7/2019 Selection (KFogler)

18/21

AP Biology

Out of AfricaLikely migration paths of humans out of AfricaLikely migration paths of humans out of Africa

Many patterns of human traits reflect this migrationMany patterns of human traits reflect this migration

50,000ya

10-20,000ya

10-20,000ya

8/7/2019 Selection (KFogler)

19/21

AP Biology

Bottleneck effect

When large population is drasticallyreduced 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

8/7/2019 Selection (KFogler)

20/21

AP Biology

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

8/7/2019 Selection (KFogler)

21/21

AP Biology

Any Questions??