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Macroevolution Part III Sympatric Speciation TEACHER NOTES
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Macroevolution:
Part III Sympatric Speciation
Debated almost since the beginning of popular
evolutionary thought, sympatric speciation is still
a highly contentious issue. By 1980 the theory
was largely unfavorable given the void of
empirical evidence available, and more critically
the conditions scientists expect to be required.
Ernst Mayr, one of the foremost thinkers on
evolution, completely rejected sympatry outright,
ushering in a climate of hostility towards the
theory. While still debatable, well documented
empirical evidence now exists, and the
development of sophisticated theories
incorporating multilocus genetics has followed.
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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]
http://en.wikipedia.org/wiki/Sympatric_speciatio
n
Types of Speciation: A Review
• Allopatric speciation is the evolution of geographically isolate
populations into distinct species. There is no gene flow, which
tends to keep populations genetically similar.
• Parapatric speciation is the evolution of geographically adjace
populations into distinct species. Divergence occurs despite
limited interbreeding where the two diverging groups come in
contact.
• Sympatric speciation has no geographic constraint to
interbreeding.
• These categories are special cases of a continuum from zero
(sympatric) to complete (allopatric) spatial or geographic
segregation of diverging groups.
Sympatric Speciation
• Sympatric Speciation occurs
without geographic isolation,
thus it occurs at a local level.
• There is something within
the environment that keeps a
single species separated into
two or more distinct groups.
• The end result is that the two
groups evolve into separate
species.
Sympatric speciation is the process through
which new species evolve from a single ancestral
species while inhabiting the same geographic
region. In evolutionary biology and
biogeography, sympatric and sympatry are terms
referring to organisms whose ranges overlap or
are even identical, so that they occur together at
least in some places.
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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 III Sympatric Speciation TEACHER NOTES
Sympatric Speciation & Habitat Differentiatio
• Suppose that a certain
species feeds on a
particular host and only
that host.
• Next, suppose a mutation
occurs that allows it to
feed upon a different
• host.
Eventually, the species is divided into
two groups that are separated from one another.
Given enough time, speciation can occur.
• The species of treehoppers pictured above are host specific.
The first lives on bittersweet while the second lives on butternu
Treehopper ecology: Treehoppers pierce plant
stems with their beaks, and feed upon sap. The
immatures can frequently be found on
herbaceous shrubs and grasses, whereas the
adults more often frequent hardwood tree
species. Excess sap becomes concentrated as
honeydew, which often attracts ants. Some
species have a well-developed ant mutualism,
and these species are normally gregarious, as
well, which attracts more ants. The ants provide
protection from predators. Treehoppers mimic
thorns to prevent predators from spotting them.
Another example is the North American apple
maggot fly (Rhagoletis pomenella) originally it
lived in native hawthorn trees but about 200
years ago some of these flies colonized apple
trees. Because apples mature more quickly than
hawthorn fruit, natural selection favored those
apple feeding flies. These two populations are
classifies as subspecies but it is predicted in the
future they will become separate species.
Students often think the primary colors of
pigment and light are the same. They are not!
You’ve probably seen the “RGB 1, RGB 2”
designations as an LCD projector searches for a
projection source.
The Physics of Light & Speciation
• There are three primary colors of light: red, green and
blue (sorted by frequency which corresponds to energy).
• Water molecules tend to absorb reddish light, leaving
the blue light to travel towards the depths of large
bodies of water.
• Because of this, deep ocean waters look blue.
Graphichttp://evolution.berkeley.edu/evolibrary/news/09
0301_cichlidspeciation
Boughman, J. W. (2002). How sensory drive can
promote speciation. Trends in Ecology and
Evolution 17(12):571-577.
Genner, M. J., Seehausen, O., Lunt, D. H., Joyce,
D. A., Shaw, P. W., Carvalho, G. R., and Turner,
G. F. (2007). Age of cichlids: new dates for
ancient lake fish radiations. Molecular Biology
and Evolution 24(5):1269-1282.
Maan, M. E., Seehausen, O., and Van Alphen, J.
J. M. (2010). Female preferences and male
coloration covary with water transparency in a
Lake Victoria cichlid fish. Biological Journal of
the Linnean Society. 99: 398-406.
Seehausen, O., van Alphen, J. J. M., and Witte, F.
(1997). Cichlid fish diversity threatened by
Macroevolution Part III Sympatric Speciation TEACHER NOTES
eutrophication that curbs sexual
selection. Science277(5333):1808-1811.
Seehausen, O., Terai, Y., Magalhaes, I. S.,
Carleton, K. L., Mrosso, H. D. J., Miyagi, R.,
van der Sluijs, I., Schneider, M. V., Maan, M. E.,
Tachida, H., Imai, H., and Okada, N. (2008).
Speciation through sensory drive in cichlid
fish. Nature 455:620-626.
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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]
The Physics of Light & Speciation
• However, everything changes when the water is
clouded by particles.
• Just picture a silt-clogged river or lake.
• Such sediment particles are particularly good at
absorbing bluish light — the opposite of water
molecules.
• So when the sun shines on cloudy waters, blue light i
present near the surface, but just a few meters down
most of the blue light will have been absorbed and
mainly red light will penetrate.
The Physics of Light & Speciation
• The physics of light affects not just how blue water
looks to us, but how the animals living in the world's
oceans, lakes, and rivers are able to find food and eac
other — and this, in turn, can impact their evolution.
• Many fish species, for example, have evolved vision
that is specifically tuned to see well in the sort of ligh
available where they live.
• But even beyond simple adaptation, the physics of
light can lead to speciation.
The Physics of Light & Speciation
• In fact, biologists recently demonstrated that the ligh
penetrating to different depths of Africa's Lake Victor
seems to have played a role in promoting a massive
evolutionary radiation.
• More than 500 species of often brightly colored cichl
fish have evolved there in just a few hundred thousan
years!
• WHY??
Ask students to explain refraction, the bending of
light. If you need to give them some hints, ask
what happens when white light passes through a
prism. The white light is refracts white light into
the colors of the visible spectrum (ROY G BIV)
just as water droplets in the atmosphere refract
sunlight into the colors of a rainbow.
Macroevolution Part III Sympatric 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]
The Physics of Light & Speciation
• Picture a lake with slightly cloudy water. Near the surface, blue
light dominates the visual environment, but in deeper waters,
red light does.
• A fish population lives along the lake's shore where it slopes
from very shallow water to deeper water — so some of the fis
spend more of their time in blue light and some spend more o
their time in red light.
Emphasize that the “cloudy” water is due to
human impact on the environment in this
situation.
Graphichttp://evolution.berkeley.edu/evolibrary/news/09
0301_cichlidspeciation
The Physics of Light & Speciation
• Like all populations, the fish have genetic variation,
individual fish have different versions of genes.
• Some of this genetic variation affects the fishes' color
vision.
• Some fish have genes that enable them to see blue
light better, while other fish have a red light advantag
The Physics of Light & Speciation
• Because of the differential penetration of light into th
lake, fish sensitized to blue light have an advantage in
shallower waters because they can better find food
and spot predators there, while fish tuned to red ligh
have an advantage in deeper waters.
• So in different parts of the fishes' habitat, different
color-sensitivity genes are favored by natural selectio
The Physics of Light & Speciation
• By itself, natural selection acting on light sensitivity
can cause something of a rift in the population, but
when sexual selection is considered as well, the
divergence is amplified.
• Male fish have some variation in color.
• Some males have genes for blue coloration, some
have genes for red coloration.
• This matters because female fish are choosy about
their mates and tend to pick brightly colored males to
father their offspring.
Humans have varying light intensity preferences
as well. Some folks are sensitive to bright
sunlight and may even have their eyes water if
they don’t wear tinted lenses.
Over many generations, if the fish don't move
too much within their range, blue sensitivity will
evolve to be more common among fish living
near the surface and red sensitivity will become
more common among fish living further down
the slope. Emphasize to students that these two
groups of fish are essentially separated—even
though the separation does not result from a
geographic barrier.
Macroevolution Part III Sympatric 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]
The Physics of Light & Speciation
In this scenario, blue males
living in deep waters would
have trouble finding mates for
two reasons:
(1) there is little blue light
around, so they look more dull
than red males, and
(2) the females living in deep
waters tend to be less sensitive
to blue light than they are to
red.
Ask students which colored male has the distinct
advantage. Red males living in deep water would
be winners on both counts: their coloration
makes the most of the available red light, and the
females living at those depths tend to carry genes
that make them extra-sensitive to red light.
The Physics of Light & Speciation
• Over many generations of
sexual selection acting in this
way, the two parts of the
population may diverge.
• Though they live right next
door to one another, the fish
will evolve to prefer to mate
with other fish that share
their coloration, lightsensitivity, and habitat.
Bottom-dwelling blue fish face a long series of
lonely nights, while bottom-dwelling red fish get
all the girls. And of course, the opposite is true
near the surface. Over time, the two subpopulations may even cease to mate with one
another entirely and evolve enough differences to
be considered separate species.
Sympatric Speciation: Habitat Differentiation and
Sexual Selection
Graphichttp://evolution.berkeley.edu/evolibrary/news/09
0301_cichlidspeciation
GREAT video clip at : http://youtu.be/Trcq392NwU If that site is blocked, try this one:
http://evolution.berkeley.edu/evolibrary/news/09
0301_cichlidspeciation
Sympatric Speciation: Polyploidy
• Polyploidy refers to instant
speciation which occurs in most
often in plants.
• Polyploid cells and organisms are
those containing more than two
paired (homologous) sets of
chromosomes.
• Polyploidy may occur due to
abnormal cell division, either
during mitosis, or commonly
during metaphase I in meiosis.
Review the concept of nondisjunction of
chromosomes during meiosis. True polyploidy
rarely occurs in humans, although it occurs in
some tissues (especially in the liver). Aneuploidy
is more common.
Polyploidy occurs in humans in the form of
triploidy, with 69 chromosomes (sometimes
called 69,XXX), and tetraploidy with 92
chromosomes (sometimes called 92,XXXX).
Triploidy, usually due to polyspermy, occurs in
about 2–3% of all human pregnancies and ~15%
of miscarriages.[citation needed] The vast
majority of triploid conceptions end as
miscarriage and those that do survive to term
typically die shortly after birth. In some cases
survival past birth may occur longer if there is
mixoploidy with both a diploid and a triploid cell
population present.
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LO 3.24 The student is able to predict how a change in genotype, when expressed as a phenotype, provides a variation that can be
subject to natural selection. [See SP 6.4, 7.2; Essential knowledge 3.C.1]
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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 III Sympatric Speciation TEACHER NOTES
Sympatric Speciation: Polyploidy
• Autopolyploidy refers to the occurrence in which the
number of chromosomes double in the offspring due
total non-disjunction during meiosis.
• This was discovered by Hugo deVries when studying
primroses.
• He noticed some of
them were larger and
very hardy.
Sympatric Speciation: Polyploidy
• The normal primrose is
diploid with 14
chromosomes. 2N = 14
• In this species there was
a total nondisjunction
event resulting in
primroses that are
tetraploid. 4N = 28
• These primroses cannot
successfully mate with
the diploid species.
Sympatric Speciation: Autopolyploidy
This is the mechanism for autopolyploidy. A diploid plant
becomes a tetraploid plant. The offspring look very much like th
diploid plant but may be a little larger and more vigorous.
Autopolyploids are polyploids with multiple
chromosome sets derived from a single species.
Autopolyploids can arise from a spontaneous,
naturally occurring genome doubling, like the
potato. Others might form following fusion of 2n
gametes (unreduced gametes). Bananas and
apples can be found as autotriploids.
Autopolyploid plants typically display polysomic
inheritance, and are therefore often infertile and
propagated clonally perfect.
Graphic Campbell;
http://en.wikipedia.org/wiki/Polyploid#Autopoly
ploidy
Sympatric Speciation: Allopolyploidy
• Allopolyploids are polyploids with chromosomes
derived from different species.
• Precisely, it is the result of multiplying the
chromosome number in an F1 hybrid.
Graphic from Campbell
Emphasize that is possible that allopolyploidy
plants could be a result of two plants that
undergo total nondisjunction like autopolyploidy
but that is not likely. Allopolyploidy plants are
usually more vigorous than the parents.
Examples plants that are a result of
allopolyploidy are oats, potatoes, bananas,
barley, plums, apples, sugar cane, coffee and
wheat.
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LO 3.24 The student is able to predict how a change in genotype, when expressed as a phenotype, provides a
variation that can be subject to natural selection. [See SP 6.4, 7.2; Essential knowledge 3.C.1]
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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 III Sympatric Speciation TEACHER NOTES
Sympatric Speciation: Chromosomal Rearrangements
Humans started synthesizing new species of plants in the
laboratories of Sweden and Scotland during the 19th century.
Triticale was among the first synthetic plants. As a rule, triticale
combines the high yield potential and good grain quality of
wheat with the disease and environmental tolerance (including
soil conditions) of rye.
Chromosomal rearrangements encompass several
different classes of events: deletions,
duplications, inversions; and translocations. Each
of these events can be caused by breakage of
DNA double helices in the genome at two
different locations, followed by a rejoining of the
broken ends to produce a new chromosomal
arrangement of genes, different from the gene
order of the chromosomes before they were
broken. Consistent with the origin of
chromosomal rearrangements by breakage,
rearrangements can be induced artificially by
using ionizing radiation. This kind of radiation,
of which X rays and gamma rays are the most
commonly used, is highly energetic and causes
numerous double-stranded breaks in DNA.
Graphichttp://orthoptera.speciesfile.org/Common/basic/S
howAllImages.aspx
Another example is the giant panda which has
been mystery for years. They look like bears but
have many differences:
Sympatric Speciation: Chromosomal Rearrangements
In the 1960's Australian biologist
M.J.D. White was studying two
neighboring flightless grasshoppers.
They appeared to be identical in
form but showed clear differences in
the configuration of their
chromosomes.
It appeared that there had been a random change in the
chromosome structure that did not result in a lethal zygote. Thos
grasshoppers possessing it were more fit for certain areas of the
grasshoppers' range. These are now two different species of the
genera Vandiemenella.
1. They bleat instead of roar
2. They have a flattened face
3. They eat bamboo instead of eating meat and
vegetable matter
4. They have 6 digits on their hands instead of 5.
(The sixth is actually an extended wrist bone.)
5. They have larger forelimbs and shoulder than
their hind limbs.
6. They have 42 chromosomes with the
centromeres located in the middle instead of 74
with the centromere on the ends.
Upon examination, it was found that each brown
bear chromosome matched up with an arm of a
panda bear chromosome. This suggests that the
panda bear chromosome is a result of a fusion
between two brown bear chromosomes.
Macroevolution Part III Sympatric Speciation TEACHER NOTES
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Tempo of Evolution: Gradualism
When evolution occurs in this mode, it is usually
by the steady transformation of a whole species
into a new one (through a process called
anagenesis). In this view no clear line of
demarcation exists between an ancestral species
and a descendant species, unless splitting occurs.
Graphic- Campbell
Time
• When speciation
occurred or is
completed usually
cannot be determined
with respect to
gradualism.
• The seasonal isolating
mechanism is a good
example.
Tempo of Evolution: Punctuated Equilibrium
• Punctuated equilibrium was
first proposed by Stephen Jay
Gould and Niles Eldredge in
1972.
• Most species will exhibit little
net evolutionary change for
most of their geological
history, remaining in an
extended state called stasis.
Time
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• Gradualism or phyletic
gradualism is a model of
evolution which theorizes
that most speciation is slow,
uniform and gradual.
• Evolution works on large
populations over an expanse
of time.
• The population slowly
accumulate changes and
evolves.
Tempo of Evolution: Punctuated Equilibrium
• Punctuated equilibrium occurs
after some crisis in the
environment. It may also be
accompanied by a reduction in
population size.
• Once natural selection occurs
and the population evolves, the
population may stay static for
long periods of time once again.
Punctuated equilibrium (also called punctuated
equilibria [plural form]) is a theory in
evolutionary biology which proposes that most
species will exhibit little net evolutionary change
for most of their geological history, remaining in
an extended state called stasis. When significant
evolutionary change occurs, the theory proposes
that it is generally restricted to rare and
geologically rapid events of branching speciation
called cladogenesis. Cladogenesis is the process
by which a species splits into two distinct
species, rather than one species gradually
transforming into another.
Time
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LO 1.20 The student is able to analyze data related to questions of speciation and extinction throughout the
Earth’s history. [See SP 5.1; Essential knowledge 1.C.1]
Tempo of Evolution: Gradualism
• The fossil record supports both of
these tempo types.
Graphic- Campbell
Macroevolution Part III Sympatric Speciation TEACHER NOTES
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LO 1.20 The student is able to analyze data related to
questions of speciation and extinction throughout the
Earth’s history. [See SP 5.1; Essential knowledge
1.C.1]
Gradualism vs. Punctuated Equilibrium
Taken from
http://en.wikipedia.org/wiki/Punctuated_equilibri
um
Created by:
Carol Leibl
Science Content Director
National Math and Science