1. Part III Sympatric Speciation
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.
Macroevolution:
Part III Sympatric Speciation

2. Types of Speciation: A Review
Allopatric speciation is the evolution of geographically isolated populations into distinct species. There is no gene flow, which tends to keep populations genetically similar.
Parapatric speciation is the evolution of geographically adjacent populations into distinct species. Divergence occurs despite limited interbreeding where the two diverging groups come into 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 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.

3. 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.

4. Sympatric Speciation & Habitat Differentiation
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 butternut.
Tree hopper 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.

5. 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.
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.
Graphic-
Boughman, J. W. (2002). How sensory drive can promote speciation. Trends in Ecology and Evolution 17(12):
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):
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:
Seehausen, O., van Alphen, J. J. M., and Witte, F. (1997). Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science277(5333):
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:

6. 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 is 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.
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.

7. 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 each 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 light available where they live.
But even beyond simple adaptation, the physics of light can lead to speciation.

8. The Physics of Light & Speciation
In fact, biologists recently demonstrated that the light penetrating to different depths of Africa's Lake Victoria seems to have played a role in promoting a massive evolutionary radiation.
More than 500 species of often brightly colored cichlid fish have evolved there in just a few hundred thousand years!
WHY??
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.
Graphic-
Boughman, J. W. (2002). How sensory drive can promote speciation. Trends in Ecology and Evolution 17(12):
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):
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:
Seehausen, O., van Alphen, J. J. M., and Witte, F. (1997). Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science277(5333):
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:

9. 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 fish spend more of their time in blue light and some spend more of their time in red light.
Emphasize that the “cloudy” water is due to human impact on the environment in this situation.
Graphic-
Boughman, J. W. (2002). How sensory drive can promote speciation. Trends in Ecology and Evolution 17(12):
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):
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:
Seehausen, O., van Alphen, J. J. M., and Witte, F. (1997). Cichlid fish diversity threatened by eutrophication that curbs sexual selection. Science277(5333):
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:

10. 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 advantage.
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.

11. The Physics of Light & Speciation
Because of the differential penetration of light into the 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 light have an advantage in deeper waters.
So in different parts of the fishes' habitat, different color-sensitivity genes are favored by natural selection.
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.

12. 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.

13. 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. 

14. 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, light-sensitivity, 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 sub-populations may even cease to mate with one another entirely and evolve enough differences to be considered separate species.

15. Sympatric Speciation: Habitat Differentiation and Sexual Selection
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GREAT video clip at : If that site is blocked, try this one:

16. 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.

17. Sympatric Speciation: Polyploidy
Autopolyploidy refers to the occurrence in which the number of chromosomes double in the offspring due to total non-disjunction during meiosis.
This was discovered by Hugo deVries when studying primroses.
He noticed some of them were larger and very hardy.

18. 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.

19. Sympatric Speciation: Autopolyploidy
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;
This is the mechanism for autopolyploidy. A diploid plant becomes a tetraploid plant. The offspring look very much like the diploid plant but may be a little larger and more vigorous.

20. Sympatric Speciation: Allopolyploidy
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.
Allopolyploids are polyploids with chromosomes derived from different species.
Precisely, it is the result of multiplying the chromosome number in an F1 hybrid.

21. 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.

22. 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.
Graphic-
Another example is the giant panda which has been mystery for years. They look like bears but have many differences:
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.
It appeared that there had been a random change in the chromosome structure that did not result in a lethal zygote. Those grasshoppers possessing it were more fit for certain areas of the grasshoppers' range. These are now two different species of the genera Vandiemenella.

23. Tempo of Evolution: Gradualism
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.
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

24. Tempo of Evolution: Gradualism
When speciation occurred or is completed usually cannot be determined with respect to gradualism.
The seasonal isolating mechanism is a good example.
Time

25. 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
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.
Graphic- Campbell

26. 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.
The fossil record supports both of these tempo types.
Time
Graphic- Campbell

27. Gradualism vs. Punctuated Equilibrium
Taken from

28. Created by:
Carol Leibl
Science Content Director
National Math and Science