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Part I
Macroevolution
Macroevolution- is the process of speciation
or making a new 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.
If a new species evolves, then for some reason
it can no longer interbreed with the species it
was once a part of. This is due to changes in
the gene pool and microevolution.
Macroevolution- is the process of
speciation or making a new 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.
If a new species evolves, then for some
reason it can no longer interbreed with
the species it was once a part of. This is
due to changes in the gene pool and
microevolution.
These closely related animals are in the genus
Canis but do not interbreed with one another in
nature. They are separate species.
Speciation-2 types
I. Anagenesis- is the accumulation of changes in
one species that leads to another species. The
changes that accumulated from the
Hyacotherium-> Equus (modern horse) is an
example of anagenesis.
Speciation-2 types
I. Anagenesis- is the accumulation of
changes in one species that leads to
another species. The changes that
accumulated from the Hyacotherium->
Equus (modern horse) is an example of
anagenesis.
II. Cladogenesis- is the budding of a one or more new species
from a species that continues to exists. This results in biological
diversity.
a. Allopatric speciation-Speciation occurs because a group has
been separated from the parent group.
b. Sympatric speciation-speciation occurs even though the two
groups are still living in the same area.
Sympatric-Living in the same geographic area
Allopatric-Groups living in 2 different geographic areas
II. Cladogenesis- is the budding of a one or more new
species from a species that continues to exists. This
results in biological diversity.
a. Allopatric speciation-Speciation occurs because a
group has been separated from the parent group.
b. Sympatric speciation-speciation occurs even though
the two groups are still living in the same area.
Sympatric-Living in the same geographic area
Allopatric-Groups living in 2 different geographic areas
A. Allopatric Speciation- First step
1. Geographic Isolation-(extrinsic isolating
mechanism). Two populations must become
geographically isolated from one another. If the groups
become sympatric again one of two things resultA. They have become separate species, and they can no
longer interbreed
B. They have not changed enough and still can
interbreed They remain the same species.
Islands produce some of the most profound examples
of speciation due to geographic isolation.
A. Allopatric Speciation- First step
1. Geographic Isolation-(extrinsic isolating mechanism).
Two populations must become geographically isolated
from one another. If the groups become sympatric again
one of two things resulta. They have become separate species, and they can no
longer interbreed
b. They have not changed enough and still can interbreed
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. Founder effect- The population that left the original
group will have different allelic make-up from the
original group
2. The 2 groups will now experience different mutations
3. The 2 groups will now experience different selection
pressures being in different environments.
i.e.The classic example are the finches of the Galapagos
Islands. There are 14 different species of finches and 25
islands. 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 going to a new area and
evolving into several new species is called adaptive
radiation.
Why does speciation occur after geographic isolation
1. Founder effect- The population that left the original
group will have different allelic make-up from the original
group
2. The 2 groups will now experience different mutations
3. The 2 groups will now experience different selection
pressures being in different environments.
i.e.The classic example are the finches of the Galapagos
Islands. There are 14 different species of finches and 25
islands. 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 going to a new area and
evolving into several new species is called adaptive
radiation.
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 group 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.
Darwin found 14 different species of finches in
these islands. He also saw adaptive radiation in
tortoises and the mocking bird on the
Galapagos Islands.
How it happens-Changes occur so that 1. interbreeding
does not occur or 2. no viable offspring or 3. no fertile
offspring in nature
1. Ecogeographic isolation- The two populations have
become so specialized for different environments, that
once the barrier is removed the 2 species will never
become sympatric.
Species A can not live where species B lives. Their
genetic differences prevents gene flow
Ex.Plantus occidentalis (sycamore) found in the eastern
United States and.
Plantus orientalis (oriental plane tree) found in the
Mediterranean area can form fertile hybrids but these
areas are so different from one another that they can
survive in one another's habitat
How it happens-Changes occur so that 1.
interbreeding does not occur or 2. no viable
offspring or 3. no fertile offspring in nature
1. Ecogeographic isolation- The two populations
have become so specialized for different
environments, that once the barrier is removed the
2 species will never become sympatric. Species A
can not live where species B lives.
Ex. Plantus occidentalis (sycamore) found in the
eastern United States and.
Plantus orientalis (oriental plane tree) found in the
Mediterranean area can form fertile hybrids but
these areas are so different from one another that
they can survive in one another's habitat
2. Habitat isolation- the two species have
developed a preference for 2 different
habitats. Even if the species become
sympatric, the probability that they will meet
and mate is low.
Ex-Bufo woodhousei and Bufo americanus are
2 closely related toads. B. woodhousei likes
to reproduce in quiet water of stream whereas
B. americanus likes to reproduce in shallow
rain-pools. They remain separate species.
2. Habitat isolation- the two species have
developed a preference for 2 different
habitats. Even if the species become
sympatric, the probability that they will
meet and mate is low.
Ex-Bufo woodhousei and Bufo
americanus are 2 closely related toads.
B. woodhousei likes to reproduce in
quiet water of stream whereas
B. americanus likes to reproduce in
shallow rain-pools. They remain
separate species.
3. Seasonal isolation- the two species have
developed different times of the year to mate *if
the species become sympatric they will seldom
mate.
There are four species of frogs from the genus,
Rana, each of these frogs mates at different times
of the year.
3. Seasonal isolation- the two species have
developed different times of the year to mate
*if the species become sympatric they will
seldom mate.
There are four species of frogs from the
genus, Rana, each of these frogs mates at
different times of the year so they do not
mate with one another.
4. Behavioral Isolation- Behavior during mating is
important. If courtship behavior has changed during
separation, and now when the groups are sympatric mating
will not occur, two new species are formed.
i.e.There are 12 fiddler crabs (Uca) species found on a
beach in Panama.
The male for each species has a distinctive display which
includes waving its claw, elevating the body, and moving
around the burrow.
4. Behavioral Isolation- Behavior during mating is
important. If courtship behavior has changed during
separation, and now when the groups are sympatric
mating will not occur, two new species are formed.
i.e.There are 12 fiddler crabs (Uca) species found on
a beach in Panama.
The male for each species has a distinctive display
which includes waving its claw, elevating the body,
and moving around the burrow.
5. Mechanical isolation- There is a physical,
biological structure that prevents mating
i.e. size, fit of genitalia organs (lock and key) found
in snails, insects and plants.
6. Gametic isolation- Even if mating occurs; a
biolgical mechanism will prevent the sperm or pollen
from reaching the eggs
i.e. When Drosophila virilis and Drosophila
americanus mate, the sperm a immobilized so that
they never reach the eggs.
5. Mechanical isolation- There is a
physical, biological structure that
prevents mating
Ex. size, fit of genitalia organs (lock and
key) found in snails, insects and plants.
6. Gametic isolation- Even if mating
occurs; a biolgical mechanism will
prevent the sperm or pollen from
reaching the eggs
Ex. When Drosophila virilis and
Drosophila americanus mate, the sperm a
immobilized so that they never reach the
eggs.
The next isolating mechanisms result in an embryo
and are called a post-zygotic isolating mechanism.
This exacts significant cost from the individual.
7. Developmental isolation- If fertilization occurs,
the development of the embryo can be irregular and
the embryo dies be irregular and the embryo
aborted. When goats and sheep mate, they produce
embryos that die before birth.
8. Hybrid inviability- Even if a hybrid is produced,
it may not make it to a reproductive age because it is
weak, and irregular, etc.
i.e.When tobacco hybrids are successful, they often
result in - tumors in their vegetative parts. Usually
no flowering occurs and no reproduction occurs.
The next isolating mechanisms result in an embryo and
are called a post-zygotic isolating mechanism. This
exacts significant cost from the individual.
7. Developmental isolation- If fertilization occurs, the
development of the embryo can be irregular and the
embryo dies be irregular and the embryo aborted. When
goats and sheep mate, they produce embryos that die
before birth.
8. Hybrid inviability- Even if a hybrid is produced, it may
not make it to a reproductive age because it is weak,
and irregular, etc.
i.e.When tobacco hybrids are successful, they often
result in - tumors in their vegetative parts. Usually no
flowering occurs and no reproduction occurs.
9. Hybrid sterility- some hybrids produce superior offspring
but the offspring are sterile
A mule is the result of female horse crossed with a male
donkey. Mules are sterile- (Hinny is the offspring of a female
donkey and a male horse) *no gene flow
Horse is on the left, donkey is in the center and the mule is on
the right.
9. Hybrid sterility- some hybrids produce superior
offspring but the offspring are sterile
A mule is the result of female horse crossed with a
male donkey. Mules are sterile- (Hinny is the offspring
of a female donkey and a male horse) *no gene flow
Horse is on the left, donkey is in the center and the mule
is on the right.
II.Sympatric Speciation-no geographic isolation is
necessary.
Polyploidy-instant speciation and occurs in plants.
1. Autopolyploidy- the number of chromosomes double
in the offspring due to total nondisjunction during
meiosis
i.e. Primrose- 2N=14 chromosomes. Nondisjunction
occurrs and there are now primroses that are
teteraploid. 4N=28 discovered by Hugo deVries.
II.Sympatric Speciation-no geographic isolation
is necessary.
Polyploidy-instant speciation and occurs in
plants.
1. Autopolyploidy- the number of chromosomes
double in the offspring due to total
nondisjunction during meiosis
i.e. Primrose 2N=14 chromosomes.
Nondisjunction occurrs and there are now
primroses that are tetraploid. 4N=28 discovered
by Hugo deVries.
2. Allopolyploidy- involves the multiplication(doubling)
of the number of chromosomes in a hybrid between 2
species due to nondisjunction.
Ex-Plant A has 12 chromosomes and plant B has 8
chromosomes. Nondisjunction occurs and the egg has
12 chromosomes instead of 6. The pollen has 8
chromosomes instead of four. When plant A pollinates
plant B the resulting new seed and then plant will have
a total of 20 chromosomes.
Alloploidy plants are usually more vigorous than the
parents. Examples are oats, potatoes, bananas, barley,
plums, apples, sugar cane, coffee and wheat.
2. Allopolyploidy- involves the
multiplication(doubling) of the number of
chromosomes in a hybrid between 2 species due to
nondisjunction.
Ex-Plant A has 12 chromosomes and plant B has 8
chromosomes. Nondisjunction occurs and the egg
has 12 chromosomes instead of 6. The pollen has 8
chromosomes instead of four. When plant A
pollinates plant B the resulting new seed and then
plant will have a total of 20 chromosomes.
Allopolyploidy plants are usually more vigorous than
the parents. Examples are oats, potatoes, bananas,
barley, plums, apples, sugar cane, coffee and wheat.
The tempo of evolution
1. Gradualism- (Darwin) evolution works on
large populations over a large expanse of time.
The populations slowly accumulate changes
and evolve.
2. Punctuated equilibrium-(Gould) evolution is
often rapid. This change occurs after some
crises in the environment. This may reduce the
population size. Once natural selection occurs
and populations evolve, then the population
may stay static or not change for long periods
of time.
The tempo of evolution
1. Gradualism-(Darwin) evolution
works on large populations over
a large expanse of time. The
populations slowly accumulate
changes and evolve.
2. Punctuated equilibrium(Gould) evolution is often rapid.
This change occurs after some
crises in the environment. This
may reduce the population size.
Once natural selection occurs
and populations evolve, then the
population may stay static or not
change for long periods of time.
The fossil record supports both
tempos.
Let’s see what we know
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