1. What changes populations?
Evolutionary Forces
What changes populations?
(Ch. 23)

2. Forces of evolutionary change
Natural selection
traits that improve survival or reproduction accumulate in the population
ADAPTIVE change
Genetic drift
frequency of traits changes in a population due to chance events
RANDOM change

3. Natural Selection
Selection acts on any trait that affects survival or reproduction
predation selection
physiological selection
sexual selection

4. Predation Selection Predation selection act on both predator & prey
behaviors
camouflage & mimicry
speed
defenses (physical & chemical)

5. 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 producing anti-freeze protein
5.5 mya The Antarctic Ocean freezes over

6. Physiological selection
Dogs pee on trees…Why don’t trees pee on dogs?
NH3
plant nutrient
animal waste
One critter’s trash is another critter’s treasure!

7. Okay, but how to
explain this?!?!?

8. Survival doesn’t matter if you don’t reproduce!
Sexual Selection
Acting on reproductive success
attractiveness to potential mate
fertility of gametes
successful rearing of offspring
Survival doesn’t matter if you don’t reproduce!

9. It’s FEMALE CHOICE, baby!
Sexual selection
It’s FEMALE CHOICE, baby!

10. The lion’s mane…
Females are attracted to males with larger, dark manes
Correlation with higher testosterone levels
Better health
more muscle
Better fertility
longer life
But imposes a cost to male
HOT! Is it worth it??
Even though it’s very hot to have a large mane the benefit of attracting mates and successfully producing & rearing young since you have that large mane outweighs the costs.
Females who chose these males were more “successful” (more, healthier young) and therefore had a greater opportunity to pass on the trait of being attracted to longer darker manes to their daughters and the trait of having longer, darker manes to their sons.

11. Sexual dimorphism and sexual selection

12. Say About Fiddlers With
You Know What They
Say About Fiddlers With
Big Claws...
They Need Big Gloves!

13. Sexy = fitness markers

14. Is there a testable hypothesis in there?
Sexual selection
Acts in all sexually reproducing species
the traits that get you mates
influences both morphology & behavior
Can seem maladaptive
Jacanas
Is there a testable hypothesis in there?

15. Coevolution
Two or more species reciprocally affect each other’s evolution
predator-prey
competitive species
mutualism

16. DIRECTIONAL SELECTION STABILIZING SELECTION
Effects of Selection
Changes in the average trait of a population
DIRECTIONAL SELECTION
STABILIZING SELECTION
DISRUPTIVE SELECTION
giraffe neck
horse size
human birth weight
rock pocket mice

17. Genetic Drift
Chance events changing frequency of traits in a population
not adaptation to environmental conditions
founder effect
Bottleneck

18. Genetic drift Generation 1 Generation 2 Generation 3
CRCR
CRCW
CWCW
Only 5 of
10 plants
leave
offspring
Only 2 of
Generation 2
p = 0.5
q = 0.5
Generation 3
p = 1.0
q = 0.0
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW) = 0.3

19. albino deer Seneca Army Depot
Founder effect
A new population is started by a small group of individuals
just by chance some rare traitsmay be at high frequency; others may be missing
skews the gene pool of new population
example: colonization of New World
ISLANDS!!!
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!)
albino deer Seneca Army Depot

20. Distribution of blood types
Distribution of the O type blood allele in native populations of the world reflects original settlement
South & Central American Indians were nearly 100% type O for the ABO blood system. Since nothing in nature seems to strongly select for or against this trait, it is likely that most of these people are descendants of a small band of closely related "founders" who also shared this blood type

21. Distribution of blood types
Distribution of the B type blood allele in native populations of the world reflects original migration
The global frequency patterns of the type B blood allele: Note that it is highest in central Asia and lowest in the Americas and Australia. However, there are relatively high frequency pockets in Africa as well. Overall in the world, B is the rarest ABO blood allele.

22. Out of Africa Likely migration paths of humans out of Africa
According to the "Out of Africa" theory, modern humans appeared as a single African species nearly 100,000 years ago, then spread throughout the world (K.Wong, Is Out of Africa Going Out the Door?, Scientific American 281(2), August 1999).
Many patterns of human traits reflect this migration

23. Bottleneck effect
When large population is drastically reduced by a disaster
famine, natural disaster, loss of habitat…
loss of variation by chance event
narrows the gene pool

24. 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

25. Any Questions??

26. Review Questions

27. The following question refers to this information: In the year 2500, five male space colonists and five female space colonists from Earth settle on an uninhabited Earthlike planet in the Andromeda galaxy. The colonists and their offspring randomly mate for generations

28. 1. After many generations, the population on this planet has an unusually high frequency for the incidence of retinitis pigmentosa, relative to Earth's population. This is most likely due to
the founder effect.
sexual selection.
the inheritance of acquired characteristics.
mutations.
the bottleneck effect.
Answer: 1
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #16

29. 2. A balanced polymorphism exists through diversifying selection in seedcracker finches from Cameroon in which small- and large-billed birds specialize in cracking soft and hard seeds, respectively. If long-term climatic change resulted in all seeds becoming hard, what type of selection would then operate on the finch population?
diversifying selection.
directional selection
stabilizing selection
sexual selection
No selection would operate because the population is in Hardy-Weinberg equilibrium.
Answer: 2
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #58

30. In a very large population, a quantitative trait has the following distribution pattern:

31. 3. What is true of the trait whose frequency distribution in a large population appears above? It is undergoing *
directional selection.
stabilizing selection.
diversifying selection.
sexual selection.
It is not possible to say, solely from the information above.
Answer: 5
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #60
Discussion Notes for the Instructor
This would be a good question to begin the discussion of types of selection. Once the question has been answered the follow-up questions might include: What information would the students need to be able to answer the question? Would this information be different for the different answer choices?
Remind the students that evolution involves a change and without some reference point it is impossible to say.

32. The bottleneck effect
Eliminates traits whether they are beneficial or not.
Increases the overall variability in the population.
Amplifies the presence of traits that will eventually lead to extinction
Increases the adaptability of a population
Decreases the number weak organisms in the population.

33. Which of the following statements accurately describes genetic drift?
It occurs when individuals in a population drift out due to emmigration
It occurs when individuals drift in to a population due to immigration
It refers to random changes in the gene frequencies in a population due to a drop in population size
Mutations are the cause of genetic drift
Natural selection is the cause of genetic drift.