Download These animals will interbreed with one another

Macroevolution Part II Allopatric Speciation TEACHER NOTES
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Macroevolution Part II:
Allopatric Speciation
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in
gene frequency, change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential
knowledge 1.C.2]
Looks Can Be Deceiving!
• These meadowlarks look
very similar yet they are not
the same species.
• By contrast, these brittle
stars look very different from
one another, but they are
the same species.
Definition of Species
• A species is a group of interbreeding organisms
that produce viable, fertile offspring in nature.
• Members of a species will interbreed with one
another but not other organisms outside of the
species. (At least most of the time!)
One of the outcomes of evolution is the
formation of new species. What is a species?
Allow the students come up with a definition
and debate its merit. Several definitions of
macroevolution also exist depending on the
textbook you use.
• Evolving complex structures such as an eye.
• Speciation
• Evolution of whole communities.
Note the italics on “viable”! Hybrid animals
exist which also makes the information in the
second bullet need some qualifiers! Now is a
good a time as any to see if students know
about hybrids at all and/or can list any. This
site has photos of the “Top Twenty” most
popular animal hybrids:
http://www.buzzfeed.com/toyota/the-20coolest-hybrid-animals-3d8x A zebroid (zebra
and equine) and donkra (donkey and zebra) are
pictured. Hybrids will be revisited later as well.
Macroevolution vs. Microevolution
• Macroevolution is evolution on a scale of
separated gene pools.
• Macroevolutionary studies focus on change that
occurs at or above the level of species, in
contrast with microevolution, which refers to
smaller evolutionary changes (typically
described as changes in allele frequencies)
within a species or population.
Asexual Species
If there is no interbreeding, how can this be a
species? Even though asexual groups do not
exchange genes, they do form recognizable
Most have evolved from a sexual
species. Only those whose phenotyp
is best adapted to the environment, groups. Most have evolved from a sexual
will continue to survive. However, it
species. Only those whose phenotype is best
makes them less adapted to
environmental change.
adapted.
Dandelions are asexual. The pollen
Asexual Species
Even though asexual groups do not
exchange genes, they do form
recognizable groups.
sterile and the egg is diploid.
Macroevolution Part II Allopatric Speciation TEACHER NOTES
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene
frequency, change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge
1.C.2]
Ring Species
• A ring species is a connected series of neighboring
populations, each of which can interbreed with closely
sited related populations, but for which there exist at
least two "end" populations in the series.
• These end populations are too distantly related to
interbreed, though there is a potential gene flow betwe
each "linked" species.
• Such non-breeding, though genetically connected, "en
populations may coexist in the same region thus closin
a "ring".
Examples forthcoming…
Ring Species
• Ensatina escholtzi is a
salamander ring species
that has a range along the
coast and inside range of
California.
• All along this range, the
salamanders interbreed, but
the salamanders on the
ends of the ring do not
interbreed.
• Their groupings are called
subspecies.
Ring Species
• The blue zones represent
where interbreeding is
occurring.
• So are there is gene flow
all along the salamander’s
range, yet the ends of the
rings do not interbreed.
Are they the same
species?
If the ends of the rings, cannot interbreed how
can this be the same species? (See next slide…)
Ring Species
They become a subspecies.
http://www.flickr.com/photos/davemedia/62430
40930/lightbox/
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene
frequency, change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Macroevolution Part II Allopatric Speciation TEACHER NOTES
Limited Interbreeding
• Each Canis species will
interbreed with the
domestic dog but not
readily with one another.
• This is true, even when
given the opportunity to do
so. Thus, they are not the
same species since they do
not interbreed in nature.
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These animals will interbreed with one another
but on a limited basis. So are they the same
species? No
Why not? They do not produce VIABLE
offspring.
Why not? Often it has to do with meiosis,
specifically, the chromosomes do not pair
evenly during meiosis, or gamete
formation. There is a stage during meiosis that
has to occur called homolog pairing and
crossing over, which can not occur if
chromosomes are not the same size or shape.
Limited Interbreeding
• Tigers and lions will interbreed in captivity, but they
do not interbreed in nature.
• Lions form groups or prides and live in the grasslands
• Tigers are more solitary and live in the forests.
• Tiglon are products of male tigers and female lions.
• Ligers are the opposite cross.
These animals will interbreed with one another
but on a limited basis. So are they the same
species? No. How do we know? The offspring
are not viable.
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Cladogenesis vs. Anagenesis
I.
Anagenesis- is the accumulation
of changes in one species that
leads to another species. It is the
lineage of a species. Over time a
species may accumulate enough
changes that it is considered a
species that differs from the
ancestral species.
II. Cladogenesis- is the budding of
one or more new species from an
ancesteral species that continues to
exists. This results in biological
diversity.
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Allopatric vs. Sympatric Speciation
Allopatric speciationSpeciation occurs because a
given group has been separated
from the parent group, usually
because of a geographic
separation as time goes by.
Sympatric speciationspeciation occurs even though
the two groups are still living in
the same area.
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Graphic-Campbell
From Latin: Allo = “different” and Patric =
Father (meaning “fatherland” in this case), so
Allopatric translates as “different fatherland”
meaning the varieties evolved in different
geographical locations.
Sym = “same” so Sympatric translates as
“same fatherland”
Macroevolution Part II Allopatric Speciation TEACHER NOTES
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LO 1.26 The student is able to evaluate given data sets
that illustrate evolution as an ongoing process. [See
SP 5.3; Essential knowledge 1.C.3]
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LO 1.24 The student is able to describe speciation in an isolated population and
connect it to change in gene frequency, change in environment, natural selection
and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Allopatric Speciation
• First, geographic isolation occurs. This is an extrinsic isolating
mechanism.
• The two populations must become isolated geographically from
one another.
• If the groups become sympatric again one of two things result
Graphic-Campbell
An extrinsic is a property is one that is not
dependent on the organism in question. It is an
external factor.
Allopatric Speciation
1. They become separate species, as evidenced by the fact they c
no longer interbreed.
2. They can still interbreed, thus they remain the same species.
Islands produce some of the most profound examples
of speciation due to geographic isolation.
Why does speciation occur after geographic isolation
1. The population that left the original group will hav
a different allelic make-up than the original species
thus experiencing the “founder effect”.
2. The two groups will continue to experience
different mutations.
3. The two groups will now experience genetic drift
and different selection pressures due to living in
separate and perhaps different environments.
Adaptive Radiation
• The classic adaptive radiation example involves the
finches of the Galapagos Islands.
• There are 14 different species of finches and 13 main
islands, 3 smaller islands, and 107 rocks and islets.
These finch populations are often referred to as
“Darwin’s Finches”. Also, you can find
varying numbers of the different species
throughout the literature. Note that only 10 of
the species are pictured here.
Adaptive Radiation
These finch populations are often referred to as
“Darwin’s Finches”. This slide shows a
common South American ancestor and 14 other
species that “radiate” from the original
immigrant finch.
Macroevolution Part II Allopatric Speciation TEACHER NOTES
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LO 1.26 The student is able to evaluate given data sets that illustrate evolution as an ongoing process. [See SP 5.3; Essential knowledge
1.C.3]
Adaptive Radiation
• One would expect that each
island would have only one
species, however, each island
has more than one species of
finch and larger islands may
have as many as ten.
• The process one species
inhabiting a new area and
evolving into several new
species is called adaptive
radiation.
The Amazing Galapagos Islands
One would expect one species of finches on
each island but that is not true. Each island has
at least three species of finches and some
islands as many as 10 species.
Adaptive Radiation
• Lets suppose that finch species A, from South
America migrates to an island .
• Finch species A would undergo speciation into finch
species B due to one or more of the following:
– The Founder effect
– Varying selection pressures
– Varying mutations
Explain that there are the three most common
“reasons” speciation occurs.
Adaptive Radiation
• Now let’s suppose that some of the new finch species
B migrate over to a second island.  (speciation) &
 (migration)
• The finches in this new environment are
geographically isolated from the other island and now
will evolve into finch species C for the same three
basic reasons. (Founder effect, varying selection pressures,
or varying mutations.)
Adaptive Radiation
• Now some of the newly evolved finch species C  make their
way to yet another new island. 
• Guess what? Yep! Once again finch species C will evolve into
finch species D (not shown yet) for the same three reasons.
(Founder effect, varying selection pressures, or varying
mutations.)
• But suppose some of species C make it back to the first island
 (The plot thickens…)
Graphic Campbell
Macroevolution Part II Allopatric Speciation TEACHER NOTES
Adaptive Radiation
• Obviously, species C is different from finch species B thus
they can no longer interbreed back on the original island.
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LO 1.26 The student is able to evaluate given data sets that illustrate evolution as an ongoing process. [See SP 5.3; Essential
knowledge 1.C.3]
• Finch species C may or may not evolve into another speci
• If there is a niche similar to that of the second island, the
selection pressure may also be similar and species C may
slow to change.
• So, both first and second islands will have species C. The
third island will have a new species D.
Adaptive Radiation
• Now lastly, lets suppose that finch species D from the
third island returns to the first and second islands. (
& )
• On the second island finch species D does not
change because it finds a niche similar to the third
island so no selection pressure is exerted upon it.
Adaptive Radiation
• Alas, the first island has no such niche. Now, there
exists a selection pressure on finch species D causing
to evolve (character displacement) into species E. 
• As a result, the first island now has three different
species of finches. Two of which are not found on
other islands (B & E). Each species has a distinct
habitat with different food sources. This process is
called adaptive radiation and most commonly involve
islands.
The Amazing Galapagos Islands
So, NOW we understand how it is possible that each island has mor
than one finch species. Some islands actually have as many as 10
species. Examine the map once more.
Character displacement refers to the
phenomenon where differences among similar
species whose distributions overlap
geographically are accentuated in regions
where the species co-occur but are minimized
or lost where the species’ distributions do not
overlap. This pattern results from evolutionary
change driven by competition among species
for a limited resource (e.g. food). The rationale
for character displacement stems from the
competitive exclusion principle, also called
Gause's Law, which contends that to coexist in
a stable environment two competing species
must differ in their respective ecological niche;
without differentiation, one species will
eliminate or exclude the other through
competition.
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LO 1.26 The student is able to evaluate given data sets that illustrate evolution as an ongoing process. [See SP 5.3; Essential knowledge
1.C.3]
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene frequency, change in
environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Macroevolution Part II Allopatric Speciation TEACHER NOTES
The Amazing Finches From the Galapagos Islands
Differences are found among
beaks and feathers of the finch
Darwin found 14 different spe
of finches inhabiting these isla
which are a result of adaptive
radiation.
There are finches that eat seed
cacti, insects and other interes
foods.
He also observed adaptive
radiation among the tortoises
mocking birds.
The Amazing Finches From the Galapagos Island
1.Vegetarian Finch
8. Cactus ground finch
2. Warbler finch
9. Cocos finch
3. Large insectivorous tree finch
10. Woodpecker finch
4. Medium insectivorous tree finch
11. Large ground finch
5. Mangrove finch
12. Sharp-beaked ground finch
6. Small insectivorous tree finch
13. Medium ground finch
7. Large cactus ground finch
14. Small ground finch
Example of Natural Selection
• During droughts in the Galapagos Islands, larger seeds are mor
abundant. Finches with slightly larger beaks have an advantag
since they are able to crack larger seeds.
• Thus, natural selection favors finches with larger beaks. These
finches are more likely to survive and pass those genes on to th
next generation. A study conducted by Peter and Rosemary Gr
over a 20 year period confirmed these assertions.
Finches 1-9 are all tree finches. Finch #1 is
vegetarian and the others insects but they differ
in the types of insects they each eat which is
also reflected in the size of their beaks. On
islands where two or more of these finches
exists, the differences in the beak size is even
more pronounced. Finch #2 is in a genera all
its own as its characteristics are more warbler
like. Finch #8 has its own genera as it is the
only finch found on the Cocos island 700 km
from the Galapagos Islands. The second large
groups of finches are ground finches 10-14.
Some live on seeds and the others on cactus
flowers. Smaller beaks are specialized for
small seeds and larger beaks for large seeds.
Why would larger seeds be more abundant
during a drought? They can store more water!
Peter and Rosemary Grant conducted a study of
finches for over 20 years on an islet Daphne
Major. They studied the medium ground finch,
which is a seed eater. Its medium beak is very
good a cracking small seeds which are
produced in abundance during wet years.
During droughts, larger seeds remain. Those
finches with slightly larger beaks are at a
advantage to crack larger seeds. Their study
concluded that natural selection selects for
those larger beaks during droughts. Those birds
with larger beak are more likely to survive and
pass those genes on to the next generation.
How Does Speciation Occur
• So, two populations of
organisms are not the same
species unless they can
interbreed, and produce viab
fertile offspring in nature.
• Each Prezygotic and
Postzygotic barrier listed lef
explains HOW speciation
occurs.
Emphasize to students that these are the
mechanisms of speciation. They explain HOW
speciation occurs. Revisit the “why’s” of
speciation addressed in the first few slides of
this presentation.
Macroevolution Part II Allopatric Speciation TEACHER NOTES
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene frequency, change in
environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Prezygotic isolations (do not result in a zygote)
are intrinsic isolating mechanisms.
Prezygotic: Ecogeographic Isolation
• Ecogeographic Isolation – Two populations have become so
specialized for survival in different environments, that once
the geographical barrier is removed the two species will neve
again interbreed as one species. The adaptations for survival i
their geographic locations prevent gene flow.
Graphic
http://www.google.com/imgres?q=Plantus+occi
dentalis+(sycamore)&hl=en&noj=1&tbm=isch
&tbnid=qbC7HYS29yBgOM:&imgrefurl=http:
//www.fcps.edu/islandcreekes/ecology/america
n_sycamore.htm&docid=7iiMHTDkfpwtTM&i
mgurl=http://www.fcps.edu/islandcreekes/ecolo
gy/Plants/sycamore/platanus_occidentalis2.jpg
&w=239&h=360&ei=xABrUJeaEsHUqgHPno
HQDg&zoom=1&iact=rc&dur=324&sig=1151
59201469248240313&page=1&tbnh=157&tbn
w=104&start=0&ndsp=18&ved=1t:429,r:12,s:
0,i:111&tx=42&ty=88&biw=1350&bih=719
Prezygotic: Ecogeographic Isolation
• The Plantus occidentalis (sycamore tree) is found in
the eastern United States and the Plantus orientalis
(oriental plane tree) is found in the Mediterranean are
• They can form fertile hybrids when artificially crossed
but are so different from one another that neither tree
can survive in the other's habitat.
Another example: The dragonflies Progomphus
obscurus and Progumphus alachuensis are
Habitat isolation- tw
species have develop closely related. In places where their range
a preference for two
different habitats. Ev overlaps, P. obscurus reproduces in streams
if the species become
sympatric, the
whereas P. alachuensis reproduces in lakes.
Prezygotic: Habitat Isolation
probability that they
will meet and mate is
low.
Example: Bufo woodhousei and Bufo americanus are two closely
related toads. B. woodhousei prefers to reproduce in the quiet wate
of a stream whereas B. americanus prefers to reproduce in shallow
rain-pools. As a result, they remain separate species.
Prezygotic: Seasonal Isolation
Seasonal isolation- the two species have developed different times
the year to mate.
Example: There are four species of frogs from the genus, Rana, eac
of these frogs mates at different times of the year so that if they are
sympatric, no interbreeding occurs.
Another example: Two species of buckthorn
shrubs, Ceanothus thysifbrus and Canothus
denatus have ranges that overlap in California
but C. thysifbrus is found in moist hills with
good soil and C. denatus is found in drier, poor,
and shallow soil.
Another examplePinus radiata and Pinus muricana-are 2 closely
related pine trees in California. While capable
of cross breeding, they seldom do but because
P. radiata sheds its pollen February and P.
muricana shed its pollen in April.
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene
frequency, change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Macroevolution Part II Allopatric Speciation TEACHER NOTES
Prezygotic: Behavioral Isolation
Behavioral isolation- If courtship behavior changes during
separation, then sympatric mating will not occur and two new speci
are formed.
Another example: There are four species of
leopard frogs (Rana). These frogs look very
much alike, but they have different mating
calls. When they hybridize, the embryos are
deformed.
Example: Twelve fiddler crab species inhabit a certain beach in
Panama. Males of each species have distinctive mating displays wh
include waving claws, elevating the body, and moving around the
burrow.
Prezygotic: Mechanical Isolation
Mechanical isolation- There is a physical or biological structure tha
prevents mating. For example differences in the size or fit of genita
may not allow mating. This can be found in certain snails, insects a
plants.
Example: The Bradybaena shown are two different species of snail
because the shells spiral in opposite directions, thus they are unable
mate with one another.
Prezygotic: Gametic Isolation
Gametic Isolation: The gametes are shed
simultaneously but something physical or
chemical prevents the sperm from
fertilizing the egg.
Example: Many sea urchin species shed
their gametes at the same time, but remain
evolutionarily distinct.
The formation of hybrid zygotes is
prevented because the surface proteins of
the ovule (the "lock") and sperm, or male
gametes (the "keys") of different species do
not fit together.
Graphic Campbell
Another example- When Drosophila virilis and
Drosophila americanus mate, the sperm are
immobilized so that they never reach the eggs.
In other cross mating of Drosophila the walls of
the vagina swell and kill the sperm before they
reach the eggs. Point out to the students that
this is a waste of gametes. Also, in the case of
tobacco plants there are 66 species, cross
pollination results in no fertilization since the
sperm nucleus never reaches the egg in the
female gametophyte.
Postzygotic: Developmental Isolatio
The next isolating mechanisms a
postzygotic meaning the zygote
indeed formed.
Energy and resources are wasted
in producing gametes and
subsequent zygote production, y
no offspring.
Another example-The eggs of fish can be
fertilized by other fish species sperm due to
Developmental isolation- If fertilization occurs, the development o external fertilization.
the embryo can be irregular and is thus spontaneously aborted.
Example: Sheep belong to the genus Ovis and have 54
chromosomes, while goats belong to the genus Capra and have 60
chromosomes. When goats and sheep mate, they produce embryos
that die prior to birth.
This results in malformed embryos.
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene frequency,
change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Macroevolution Part II Allopatric Speciation TEACHER NOTES
Postzygotic: Hybrid Inviability
Hybrid inviability- A hybrid is produced, but often does not
make it to reproductive age because it is weak, irregular, etc.
Example: When tobacco hybrids are successful, they often form
tumors. These tumors are located in their vegetative parts. Often
no flowering occurs, thus no reproduction occurs.
Postzygotic- Hybrid Sterility
occurs after mating species overcome prezygotic barriers (behavioral, mechanical, etc.)
to produce a zygote. The barrier emerges from
the cumulative effect of parental genes; these
conflicting genes interfere with the embryo’s
development and prevent its maturation. Most
often, The hybrid embryo often dies before
birth. However, sometimes, the offspring
develops fully with mixed traits, forming a
frail, often infertile adult. This hybrid displays
reduced fitness, marked by decreased rates of
survival and reproduction relative to the parent
species. The offspring fails to compete with
purebred individuals, limiting genes flow
between species.
Graphic
http://www.google.com/imgres?q=tumors+foun
d+on+tobacco+plants&hl=en&sa=X&biw=812
&bih=667&tbm=isch&prmd=imvns&tbnid=5J
A7A8h6BrZqM:&imgrefurl=http://web.williams.ed
u/Biology/Faculty_Staff/lbanta/lbanta.shtml&d
ocid=xeUYYhBnBa_JTM&imgurl=http://web.
williams.edu/Biology/Faculty_Staff/lbanta/Ima
ges/tumor.gif&w=308&h=200&ei=j4lrUOL5B
KLe2AX1v4H4Cw&zoom=1&iact=hc&vpx=5
22&vpy=376&dur=7172&hovh=160&hovw=2
46&tx=125&ty=101&sig=1151592014692482
40313&page=1&tbnh=108&tbnw=166&start=
0&ndsp=12&ved=1t:429,r:11,s:0,i:108
Just for fun: Ever heard “stubborn as a mule”?
Evidently mules are actually smart and
independent or “superior” thinkers!
A male donkey is known as a “jack” and a
female donkey (or ass) is known as a jenny. So,
yes—a “jackass” is indeed a male donkey. A
Hybrid sterility- some hybrids produce superior offspring but th
offspring are sterile.
burrow is a feral donkey. A mule is the
Example: A mule is the result of female horse crossed with a ma
donkey. Mules are sterile, thus there is no potential for gene flow offspring of a male (jack) donkey and a female
In terms of evolution it is a dead end. The horse is on the left, th
horse. A hinny is the offspring of a cross
donkey is in the center and the mule is on the right.
between a female donkey and a male horse and
is rare.
Macroevolution Part II Allopatric Speciation TEACHER NOTES
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LO 1.24 The student is able to describe speciation in an isolated population and connect it to change in gene frequency,
change in environment, natural selection and/or genetic drift. [See SP 7.2; Essential knowledge 1.C.2]
Postzygotic: Selective Hybrid Eliminatio
Selective hybrid elimination or hybrid breakdown occur
if two species are sympatric and can hybridize, and their
offspring can reproduce.
One of the following two things will happen:
1. The hybrids are as viable or as fit as the parents and
gene flow will occur and the two species will becom
one again.
2. The hybrids are weaker or have lower fitness than th
parents and will be selected against.
Postzygotic: Selective Hybrid Eliminatio
• Natural selection will select for
those individuals that will mate with
their own species and the hybrids
will die out. The competition
between the two species will cause
character displacement.
• Example: the offspring of rice
hybrid are not as fit as the parents.
Crosses between the purebred
parents will be favored.
Summary of Prezygotic Barriers
When allopatric speciation occurs, usually more than one isolation
mechanism also occurs and more than one trait will change between
the two populations.
The rationale for character displacement stems
from the competitive exclusion principle, also
called Gause's Law, which contends that to
coexist in a stable environment two competing
species must differ in their respective
ecological niche; without differentiation, one
species will eliminate or exclude the other
through competition.
Be sure to tell the students that some of the
terminology changes from text to text. Seasonal
isolation is also known as temporal isolation.
Clarify that extrinsic mechanisms are external
mechanisms and intrinsic mechanisms directly
affect the organism. Geographic isolation is
extrinsic and the ten prezygotic and postzygotic
mechanisms are intrinsic.
Students should now know WHY speciation
occurs upon geographic isolation and HOW
speciation occurs after geographic isolation.
Summary of Postzygotic Barriers
Graphic Campbell
Hybrid sterility is reduced hybrid fertility.
Hybrid breakdown is selective hybrid
elimination.
Postzygotic barriers keep two populations distinct, thus they are no
longer the same species and can no longer interbreed to produce
viable, fertile, offspring in nature. Again, when two population a
allopatric and changes occur, most likely more than one of the 10
barriers will occur in the population leading to speciation.
Macroevolution Part II Allopatric Speciation TEACHER NOTES
Created by:
46
Carol Leibl
Science Content Director
National Math and Science