1. Evolution & Speciation

2. Evolution
Evolution is the change in living things over long periods of time.
It may occur through the processes of natural selection and genetic drift.

3. Natural Selection
Natural selection explains why organisms are adapted to their environment.
This theory describes a natural process that can produce new adaptations and new species.

4. Natural Selection 4 conditions: Reproduction
Variation in traits between individuals
Heredity  some of this variation must be heritable (genetic)
Individuals differ in fitness (the number of offspring they produce)  some individuals are more likely to reproduce than others

5. Natural Selection
If these 4 conditions are met, then natural selection will result.
Let’s look at an example…

6. Natural Selection A cryptic moth: These moths reproduce
There is variation in their wing color pattern
This color pattern variation is heritable (offspring resemble their parents)

7. Natural Selection
4. Because they use their color pattern as camouflage from bird predators, if individuals do not match their background they will get eaten  only moths that look cryptic will survive and reproduce

8. Natural Selection Other examples: Pesticide resistant insects:
- only those that can tolerate the pesticide will survive and reproduce
- if this pesticide tolerance is heritable, then their offspring will also be tolerant to the pesticide
e.g. DDT used to be a very effective pesticide and initially wiped out ~90% of mosquitoes in India.
After about 10years, mosquitoes evolved resistance to DDT and now only ~20% of mosquitoes are wiped out by DDT.
pesticide
Surviving insects
Pesticide resistant insects

9. Natural Selection Other examples: Antibiotic resistant bacteria:
- only those that can tolerate the antibiotic will survive and reproduce
- if this antibiotic tolerance is heritable, then their offspring will also be tolerant to the antibiotic
- have become increasingly prevalent as the use of antibiotics has become widespread
e.g. About 70% of bacteria that cause infections in hospitals are resistant to at least one of the drugs most commonly used to treat infections.
Add antibiotic
Surviving bacteria
Antibiotic resistant strains

10. Natural Selection Types of selection: Directional selection
Favors one extreme and shifts the population mean
Stabilizing selection
Favors the mean and decreases variation around the mean
Disruptive selection
Favors the extremes and selects against the mean

11. Responses to Selection
# of individuals
Coloration
light dark
Directional selection
# of individuals
Coloration
light dark

12. Responses to Selection
# of individuals
Directional selection
Stabilizing selection
# of individuals
Coloration
light dark

13. Responses to Selection
# of individuals
Directional selection
Stabilizing selection
Disruptive selection
# of individuals
Coloration
light dark

14. Genetic Drift
Genetic drift is the fluctuation of genotypes in the population due to chance.
In small populations, genetic drift can result in non-adaptive evolution.

15. Genetic Drift
Genotype A
Genotype B
Population 2
6:1
Population 4
1:6
Population 1
1:1
For the population as a whole, the frequency of the 2 genotypes is 1:1
Population 3
1:1

16. Genetic Drift
Genotype A
Genotype B
Population 2
6:1
Population 4
1:6
Population 1
1:1
For the population as a whole, the frequency of the 2 genotypes is 6:1
 the frequency of genotype A has increased due to chance
Population 3
1:1

17. Genetic Drift
Genotype A
Genotype B
Population 2
6:1
Population 4
1:6
Population 1
1:1
For the population as a whole, the frequency of the 2 genotypes is 1:1
 the frequency of the 2 genotypes has remained the same due to chance
Population 3
1:1

18. Genetic Drift
Endangered species are often reduced to dangerously small numbers and restricted to small, isolated habitats.
In small populations, genetic drift erodes genetic variation which limits a species ability to adapt to environmental change (e.g. disease, global warming, etc) and increases its probability of going extinct due to chance events.

19. Speciation What is a species?
A group of interbreeding individuals of common ancestry that are reproductively isolated from other groups

20. Speciation How might speciation (formation of new species) occur?
Allopatric speciation
A barrier divides a continuous population into 2 parts
Parapatric speciation
A hybrid zone divides a continuous population into 2 connected parts
Sympatric speciation
A population splits in 2 without any geographic separation

21. Speciation Allopatric speciation Ancestral population
A physical barrier divides the ancestral population. Over time, each isolated population diverges due to natural selection or drift
Allopatric
speciation

22. Speciation Parapatric Allopatric speciation speciation
Ancestral population
A physical barrier divides the ancestral population. Over time, each isolated population diverges due to natural selection or drift
There is some kind of habitat gradient that results in locally adapted individuals.
hybrid zone
Parapatric
speciation
Allopatric
speciation

23. Speciation Parapatric speciation Sympatric speciation Allopatric
Ancestral population
The extremes in the population are selected for and there is assortative mating.
A physical barrier divides the ancestral population. Over time, each isolated population diverges due to natural selection or drift
There is some kind of habitat gradient that results in locally adapted individuals.
hybrid zone
Parapatric
speciation
Sympatric
speciation
Allopatric
speciation

24. Allopatric Speciation
Blue-headed wrasse
Isthmus of
Panama
Cortez rainbow wrasse

25. Parapatric Speciation

26. Sympatric Speciation
Is thought to have occurred in Cichlids in a lake in Central America (also in Africa).

27. The diversity of the animals we see today is the result of processes such as natural selection and genetic drift that lead to speciation over time.
Hawaiian honey-creepers