1. Evolution of Populations
Raven Ch. 21
Doonesbury - Sunday February 8, 2004

2. Populations evolve Natural selection acts on individuals
Variation results in:
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
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

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

4. 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
Fitness- Survival & Reproductive success
individuals with one phenotype leave more surviving offspring

5. Where does Variation come from?
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)
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

6. 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 (even three in 1000). These will give rise to tolerant offspring when intercrossed (Walley et al 1974).
Guppies
When evolutionary biologist John Endler began studying Trinidad's wild guppies in the 1970s, he was struck by the wide variation among guppies from different streams, even among guppies living in different parts of the same stream. Males from one pool sported vivid blue and orange splotches along their sides, while those further downstream carried only modest dots of color near their tails. Endler also observed differences in the distribution of guppy predators, and in the color and size of gravel in different stream locations.
In the wild, where predators are plentiful, male guppies become increasingly drab over generations, pushed by predation pressure toward greater camouflage.
However, the "flashier" a male guppy is, the more likely a female guppy will choose him as a mate, giving him the opportunity to pass his genes along to the next generation. This is sexual selection at work, and it is the force that pushes guppy coloration toward conspicuousness just as hard as predation pushes coloration toward drabness.
It is clear from the research of Endler and other evolutionary biologists that male guppies live in the crossfire between their enemies and their would-be mates, with the opposing forces of predation and sexual selection forever pushing the guppy coloration in opposite directions.
Target site
Decreased number of target sites
Insecticide resistance

7. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

8. Not every mutation has a visible effect.
1. Mutation & Variation
Mutation creates variation
Mutation rates in individuals are low (1 in 100,000 division)
But are constantly appearing in populations
Mutation changes DNA sequence.
As a result, may change:
Protein amino acid sequence
may change protein structure?
may change protein 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.

9. 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

10. 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?

11. 3. Non-random mating
Sexual selection

12. 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

13. 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

14. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

15. Any Questions??