1. MECHANISMS OF EVOLUTION What changes populations?

2. Write this in the top margin of your paper: Microevolution
A change in allele frequencies in a population over generations.
Population = Organisms of the
Same species,
Living in Same place,
At the Same time.

3. I.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

4. Populations evolve, individuals don’t.
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

5. 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

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

7. II.What is “fitness”?
Describes the capability of an individual of certain genotype to reproduce
Usually is equal to the proportion of the individual's genes in all the genes of the next generation
The capacity of an organism to survive and transmit its genotype to reproductive offspring as compared to competing organisms

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

9. III. 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.

10. What are the causes of variations?
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)

11. 5 Causes of variation in a population 5 Agents of evolutionary change
Changes in DNA/chromosomes
Gene Flow
Non-random mating
Genetic Drift
Selection

12. A. Variation from changes in DNA/ chromosomes
New mutations are constantly appearing
Mutation changes DNA in some way
Changes in amino acid sequence leads to:
Changes in 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.

13. Not every mutation has a visible effect.
Random changes to DNA can be
caused by:
errors in mitosis
errors in meiosis
environmental damage
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.

14. Variation in chromosomes from sexual reproduction:
Meiosis
1. Crossing over produces new genetic
combinations
2. Independent assortment of
chromosomes along metaphase plate
Random fertilization
1. Egg with unique DNA is fertilized
by sperm with unique DNA.

15. Mean beak depth of parents (mm)
Sexual reproduction results in:
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)

16. B. Gene Flow Movement of individuals & alleles in & out of populations
due to movement of
fertile individuals or
their gametes

17. Examples: seed & pollen distribution by wind & insects
migration of animals
sub-populations may have different allele frequencies
causes genetic mixing across regions
reduce differences between populations

18. 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?

19. C. Non-random mating
Sexual selection

20. How sexual selection affects populations:
Intrasexual selection: Selection within the same sex
Ex. = Males competing for opportunity
to mate with females by challenging other
males

21. Intersexual selection: Individuals of
one sex select mates of opposite
sex based on appearance or behavior.
Ex. = Female peahens choose to
mate with male peacocks with the largest and most colorful feather display

22. Show peacock video from “Evolution“
series on PBS.

23. D. 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

24. Genetic Drift
Chance events changing frequency of traits in a population
not adaptation to environmental conditions
not selection

25. 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: Settlement of East TN by
Scot and Irish immigrants
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!)

26. 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

27. 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

28. 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

29. E. 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

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

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

32. Physiological Selection
Acting on body functions
disease resistance
physiology efficiency (using oxygen, food, water)
biochemical versatility
protection from injury
5.5 mya The Antarctic Ocean freezes over

33. 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!

34. The lion’s mane…
Females are attracted to males with larger, dark manes
Correlation with higher testosterone levels
better nutrition & health
more muscle & aggression
better sperm count / fertility
longer life
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.

35. Sexual selection Acts in all sexually reproducing species
the traits that get you mates
sexual dimorphism
influences both morphology & behavior
can act in opposition to natural selection

36. How does natural selection work?
Organisms produce far more offspring than could ever survive.
Results in higher demand for water, space, nutrients, sunlight, etc.
Competition for resources results in a “struggle for survival”.
Organisms with certain variations in behavior or physical traits are more easily able to survive.
Survivors pass on their unique traits.

37. Over generations, the accumulation of changes in the heritable characteristics of a population results in evolution – the gene pool has changed.