-11.3 - 11.5 - 11.6 -Mechanisms of Evolution

Speciation Through IsolationPatterns of Evolution

1776 United States Became Independent◦ Where were the original settlers from?

Was there an abundance of variation in this population?

How has immigration had an effect on genetic variation in the US?◦ Leads to increased genetic variation in the

population by adding new alleles to the gene pool.

Think About It:

Defined:◦ The movement of alleles from

one population to another. Break it Down:

◦ New Alleles to new population, loss of alleles in another.

Increases genetic variation. How does it affect nearby

populations? What does a lack of gene

flow lead to?

Gene Flow

Small populations more likely to be affected by random chance.

Allele frequency changes due to chance is called genetic drift.

Two processes cause pop. to become small enough for this phenomenon:◦ Bottleneck effect◦ Founder Effect

Genetic Drift

Defined:◦ Genetic drift that occurs after an event greatly

reduces the size of a population.

Bottleneck Effect

Genetic drift due to a small number of individuals of a population colonizing a new area.

Founder Effect

Loss of genetic variation.◦ Less likely to be able to adapt to changes

Lethal alleles can become more common in gene pool.

Effects of Genetic Drift

Males:◦ Sperm production is constant, .: they are less

selective in the mate they choose.◦ More chances = less selective

Females:◦ Production is limited in every reproductive cycle.◦ Less chances = more selective.

Sexual selection:◦ Certain traits increase mating success.

Effect of Mating

Intrasexual:◦ Competition among

males. Intersexual:

◦ Males display traits that attract female.

◦ http://dsc.discovery.com/videos/planet-earth-jungles-birds-of-paradise.html

◦ Some traits are not adapted for survival.

Intra/Intersexual Selection

The sun’s surface is approx: 5505 degrees Celsius. Keep this in mind.

If you are standing next to a hot stove you can feel the heat.

As you get farther away you should feel less heat. That is basic science, the farther you are from a

heat source the less it affects you. The Solar Corona (an area not to far from the sun)

has a temperature of 1.5 million degrees Celsius. How is this possible?

Brain Break #1

How do we know that a miniature poodle and a great dane are the same species?

At what point would the two breeds become separate species?

11.5 Speciation Through Isolation

If gene flow stops, populations are isolated. Adaptation is never ending

◦ Leads to gene pool changes. Over time, changes add up & isolated

populations become more and more genetically different

Behavior and phenotypes may change as well.

Isolation of Populations:

Defined:◦ When members of different populations can no

longer mate successfully with one another. Analyze:

◦ The final step in becoming separate species. Discuss:

◦ Talk with your neighbor for 1 minute and come up with an example of Isolation in nature. Be prepared to share!

Reproductive Isolation

60 Seconds starts NOW!

Defined:◦ The rise of two or more species

from one existing species BUT Mr. Wilson…..!

◦ How does isolation occur so that new species can be formed?!

◦ Great Question!

Speciation

There are three ways that populations can become isolated!

Behavioral Barriers

Geographic Barriers

Temporal Barriers

Socially Awkward Penguin

Behavior changes can prevent mating between populations.

Defined:◦ Isolation caused by

differences in courtship or mating behaviors.

Examples:◦ Fireflies flash patterns◦ Chemical scents◦ Courtship songs/dances with

birds

Behavioral Isolation

Defined:◦ Physical barriers that divid a

population into two or more groups.

What kind of barriers you ask?◦ Rivers, mountains, rivers,

anything! Examples:

◦ Pacific/Atlantic species separated by the Panama Isthmus Shrimp

◦ Grand Canyon & Squirrels

Geographic Isolation

Just pretend they’re shrimp OK?!

Defined:◦ When timing prevents reproduction between

populations. Courtship period

◦ Time of Day◦ Time of Year◦ Based on competition

Example:

Temporal Isolation

Temporal Isolation

American ToadMates Early Summer

Fowlers ToadMates Late Summer

No Guarantees & You Have to Be Good at Math!

Pick a Number between 1 and 10. Multiply it by 9 Add the two Digits of the resulting number

together (if you picked 1 just deal with it) Now Subtract 5 From it…. You should have a number now…think of

the corresponding letter in the alphabet (A=1, B=2, etc.)

Brain Break #2 : I Will Try to Read Your Mind!

Pick a country that starts with that letter. Any Country… So if you had F, Finland would work.

Once you have your country use the last letter of that country and think of an animal. Finland = D = Dog

Once you have your animal take the last letter of that animals name and think of a color. Dog = G = Green!

You Have it?....ok here I go…

Brain Break #2 : I Will Try to Read Your Mind!

Mutation and Genetic Drift cannot be predicted.◦ Random Events

Natural Selection is NOT random.◦ Beneficial traits increase survival

Natural Selection has direction◦ But this direction is controlled by the environment

NOT the population

11.6 - Patterns of Evolution

Scenario:◦ Zombie Apocalypse◦ Zombies will also eat small rats◦ Humans or Rats with tough

skin pose a challenge to zombie rotted teeth.

◦ Both species begin to develop similar characteristics in their skin making it tougher.

◦ Convergent Evolution Shark/fish tails, bird / butterfly

feathers (analogous structures).

Convergent Evolution

Defined:◦ When closely related species evolve in different

directions.

Divergent Evolution

Sometimes a change in one species can result in a change in another.

Coevolution:◦ The process by which two or more species evolve

in response to changes in each other. Example:

◦ Stinging Ants & The Bull-thorn acacia

Coevolution

Competitive species can also coevolve:◦ Plants developing defense chemicals to avoid

consumption by herbivores.◦ Crabs eat snails snails develop bigger spiked

shells crabs develop more powerful claws … etc

Coevolution in competition

Defined:◦ The elimination of a species from earth.

How?◦ Failure to adapt, hunting, fishing, etc.

Extinction

Punctuated Equillibrium◦ Episodes of speciation occur suddenly◦ Followed by long periods of little evolutionary

change. Adaptive Radiation

◦ Diversification of an ancestor into many descendant species.

Speciation follows a Pattern

End of Notes