Review: a change in genes (allele freq)

that produces a phenotype that is favorable (increases fitness) in a particular environment leads to

natural selection (survive or not in that env) and thus Evolution!

• Have out your Microevolution HW. • If you did not complete it: leave your group and

go complete it. You can go through what you miss on your own after I post this power point.

• If you did your HW good job! I would like you to review your answers. Pay particular attention to #5 and the scenarios/graphs you came up with.

• This should take 10 minutes or less. Watch your time!

Types of Natural Selection

A.) Most traits are polygenic: controlled by many genes.

1.) These traits therefore have a normal distribution and a characteristic shape when phenotypes are graphed.

Ex: Height in Humans

B.) Natural Selection can change this normal distribution in 3 ways. Your challenge was to figure this out. I know it was probably pretty difficult but thinking is good for you!

1.) Directional Selection: individuals at one end of the curve have higher fitness than individuals at the middle or other end.

Directional Selection

Food becomes scarce.

KeyLow mortality, high fitness

High mortality, low fitness

Ex: Beak Size of finches

So, The population curve shifts towards one extreme of the curve. This is pretty common.

2.) Stabilizing Selection: individuals at the center of the curve have higher fitness.

So, The population curve favors the middle of the curve and you lose the extremes.

KeyPe

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of P

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ation

Birth Weight

Selection against both extremes

keep curve narrow and in same place.

Ex: Normal weight human babies vs. high or low birth weight.

Low mortality, high fitness

High mortality, low fitness

Stabilizing Selection

Human baby birth weight is the classic example.Babies that are small don’t survive as well and babies that are too big can’t get out (until C-section was developed… we could be selecting for bigger babies!)

3.) Disruptive Selection: individuals at both ends of the curve have higher fitness than individuals in the middle.

Disruptive Selection

Largest and smallest seeds become more common.

Num

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Pop

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Beak Size

Population splits into two subgroups specializing in different seeds.

Beak Size

Ex: Food goes from medium size seeds to large and small seeds. Birds with small & large beaks are now favored.

Num

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f Bird

sin

Pop

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KeyLow mortality, high fitness

High mortality, low fitness

So, The population curve increases towards two extremes. This is not as common. You should watch the Crash Course at home that I have posted at the end they have an example of a daphnia that seems to be in disruptive selection.

• http://wps.prenhall.com/wps/media/objects/1110/1136802/17_3.html this is pretty slow but it does review the 3 types of selection. Watch it now.

• Crash course discusses it too but that’s you tube so you’ll have to do that at home.

• http://www.youtube.com/watch?v=aTftyFboC_M 8:18-12:33 c.c. types of selection

Optional Review at home:

• http://www.youtube.com/watch?v=WhFKPaRnTdQ effects on allele frequency. This is also crash course. You may like a review of microevolution. Stop around 6:40 when he starts using the H-W equation.

In broader terms, these changes from generation to generation can result in speciation: the formation of new species. a. This can be thought of as descent with

modification.b. Through change from generation to generation,

one species may separate into two.c. This idea implies that ALL life originated from a

common ancestor with speciation occurring over and over again!

Remember: Two Ways to Look At Evolution

Microevolution• Changes in a gene

pool of a population

• E.g. a population accumulating longer neck genes, darker fur genes

Macroevolution• The formation of

new species or taxonomic groups

• How did animals evolve, how did mammals evolve etc.

We just finished this Moving on to this!

Macroevolution

Big Changes

Macroevolution

• Is concerned with how new taxonomic groups or species came to be

• E.g. how did mammals evolve from ancestral reptiles (taxonomic group)

Speculative, but not a leap of Faith

Phylogenic web quest!

• Go get a copy of the web quest for you and your partner (or just you if you are working alone)

• Answer all of the questions then continue this power point. Keep your web quest b/c you will be checking some of your answers. When you are done staple you and your partner’s (if you had a partner) copy together and put them in the bin.

• It should take 30 minutes or less! Watch your time.

We use Phylogenetic Trees to sort organisms

• A phylogenic tree is an evolutionary family tree.• Uses physical

traits and/or DNA

Note

Thus the answer for web quest # 4 is that it does not matter. Either order means the same thing.

This DOES NOT say Salamanders and Humans are closely related

Phylogenic tree of Vertebrates

Tips for Making Trees

• Use your brain!• Try and think, don’t just ask• Trial and error, then double

check – does your tree make sense?

• There are a LOT of species

• Phylogenetic trees get really, really complicated and extremely detailed

• So…

The Taxonomic Groups is how we organize all the organisms on the Earth!

• Domain• Kingdom• Phylum• Class• Order• Family• Genus• Species

Ex: Cat Taxonomy

• Domain–Kingdom• Phylum–Class»Order• Family• Genus• species

• Eukarya–Animalia• Chordata–Mammalia»Carnivora• Felidae• Felis• catus

ExampleFelis Catus

Felis

Pneumonic Device

• Dude–Kings• Play–Chess»On• Fancy• Gold• Sets

Or make your own!!!

Scientific Names are based on Taxonomy

• Genus species of taxonomy put together.• Ex: humans are Homo sapiens/H. sapiens• Ex: Domestic cat is Felis catus (also called Felis

domesticus, Felis silvestrus)

• So, phylogenetic trees give us the evolutionary history (the order/relationship) and taxonomy allows us to categorize the history (like the Dewey decimal system of all organisms).

• Macroevolution comes down to new species…

• OK stop here!• Now you need to pick up the Speciation Web Quest

from the front of the room. You should work through this with your partner.

• When you are done staple you and your partner’s (if you had a partner) copy together and put them in the bin.

• Then come back to this power point• If for some reason you are running low on time you

can go through the rest of this power point at home. Remember to pick up your HW.

Post web quest!

• So, hopefully you have a pretty clear picture of speciation but the following slides are for your review

What is a species?– a group of interbreeding populations that are

reproductively isolated from other groups

• Appearance can be misleading in determining a species.

Members of Different Species May Be Similar in Appearance

Fig. 16-1

Members of SAME Species May Differ in Appearance

Fig. 16-2

How Do New Species Form? • Speciation is the process by which new species

form – Speciation depends on two factors • The isolation of populations must prevent

gene flow and thus keep them similar • Genetic divergence must occur, driven by

genetic drift or natural selection

– the different pathways to speciation fall into two broad categories • allopatric speciation, the isolating

mechanism is a physical barrier • sympatric speciation, isolation occurs

without geographical separation

• Geographical separation of a population can lead to allopatric speciation (as in the web quest example of island fruit flies)– Separation can be caused by:• Geological changes such as:

– Volcanoes– Earthquakes– continental drift– change of course by rivers

–Allopatric speciation is believed to be the most common type of speciation, especially among animals

Part of a mainlandpopulation reachesto an isolated island

Divergence may eventuallybecome sufficient to causereproductive isolation

The isolated populations beginto diverge due to genetic driftand natural selection

Allopatric Isolation and Divergence

Fig. 16-9

• Isolation without geographical separation can lead to sympatric speciation too!

• Sympatric speciation may occur when a geographical area contains two distinctly different habitats. • Through natural selection, individuals of the

species specialize in one habitat or the other• Ex: apple vs. hawthorn tree

Part of a fly population that lives only on hawthorne trees moves to an apple tree

The flies living on the apple tree do not encounter the flies living on the hawthorne tree, so the populations diverge

Sympatric Isolation and Divergence

Fig. 16-10

•Now that we have defined a species & how they come about…how do we maintain a species?

Types of isolation? • 1) Behavioral Isolation: occurs when two

populations are capable of interbreeding but have differences in courtship rituals or other behaviors.

Birds of Paradise!http://www.youtube.com/watch?v=nS1tEnfkk6M

2) Geographic Isolation: occurs when two populations are separated by geographic barriers.Ex: Canyon, mountain, body of water.

Salamandershttp://video.pbs.org/video/1300397304/Watch this now

http://www.teachersdomain.org/asset/rr10_vid_reproiso/ http://www.teachersdomain.org/asset/rr10_vid_reproiso/

3) Temporal Isolation:• occurs when two populations reproduce at

different times.• Ex: orchids

• Mechanical isolation: structure of reproductive organs is different enough that mating cannot occur.

• Gametic isolation: gametes are incompatible – even if act of mating occurs, sperm cannot fertilize egg.

Hybrids…The Grey area

• This typically happens when a geographical barrier is removed. Animals that are closely related can mate and produce offspring.

• These offspring are typically sterile and/or weak

• A great example that works are mules. Strong and docile it’s a mix of the fragile horse (but easily trainable) and strong willed (but sturdy) donkey

http://en.wikipedia.org/wiki/File:Donkey_1_arp_750px.jpg

The infamous Liger

Fig. 16-8

• There is also observed and experimental evidence of speciation. One example was in your web quest!

• So, Darwin’s BIG IDEA was that natural selection takes place in populations that are isolated from one another and over LONG periods of time, small changes in allele frequencies from generation to generation can add up to BIG changes in species. This leads us again to the idea of a universal common ancestor.

• We can represent this idea with a diagram like these. This only depicts MAJOR living categories of organisms and doesn’t even include extinct organisms and their relationships!

Extinction: Why do species disappear?

• Species have a cycle!• 1. New species• 2. Stable species w/ many sub species• THIS can then lead to 1. new species OR• 3. stable species with few sub species• 4. reduction in range and numbers• 5. extinction!

What Causes Extinction? • Extinction is the death of all members of a species • At least 99.9% of all species that ever existed are

now extinct! WHA!!!• The immediate cause of extinction is probably

environmental change • habitat destruction and increased competition

among species

• Small range• Species inhabiting extremely limited ranges may

become extinct if the area is disturbed • The Devil’s Hole pupfish is found in only

one spring-fed waterhole in the Nevada desert • http://www.youtube.com/watch?v=R_dP4E

NjcL0 (watch at home)

• Wide-ranging species normally do not succumb to local environmental catastrophes

Very Localized Distribution Can Endanger a Species

Fig. 16-13

• Overspecialization– Species that develop adaptations that favor

survival in a specific environment are at risk of becoming extinct • The Karner blue butterfly feeds only on the

blue lupine plant • The habitat of the lupine has been

significantly reduced by development • Loss of the lupine will lead to extinction of

the Karner blue butterfly • Vs. The generalist species…like humans.

We can adapt to many environments!

Extreme Specialization Places Species at Risk

Fig. 16-14

• Other species– Species that are unable to exploit resources

more efficiently and effectively than their competitors may become extinct

• Habitat change and destruction– Extinctions due to prehistoric habitat change

have had a significant effect on the evolution of organisms –Human activities are the primary cause of

present-day habitat destruction • Clearing of tropical rainforests could lead

to loss of up to half of all current species over the next 50 years

HW

• 1. Do a murkie: what you are confused about or what you thought was interesting today.

• 2. Pick up your HW. If there’s time you may start it in class.

• 3. Email me how it went.• 4. Have a great day!