Post on 18-Dec-2015
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
rcen
tage
of P
opu l
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
ber o
f Bird
sin
Pop
ulati
on
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
ber o
f Bird
sin
Pop
ulati
on
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
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!