1. Agenda 10/12 Speciation Notes Speciation Video
Speciation Illustrations
Turn in: Textbook and video notes
Homework:
Origins of Life Video and Notes
Speciation WS (on website)

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.
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.

3. With your elbow partner, define species
With your elbow partner, define species. Remember to include all living organisms in your definition.

4. 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!)
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: A zebroid (zebra and equine) and donkra (donkey and zebra) are pictured. Hybrids will be revisited later as well.

5. Allopatric vs. Sympatric Speciation
Allopatric speciation-Speciation occurs because a given group has been separated from the parent group, usually because of a geographic separation as time goes by.
Sympatric speciation-speciation occurs even though the two groups are still living in the same area.
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”

6. Allopatric Speciation
First, geographic isolation occurs.
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.

7. Allopatric Speciation
They become separate species, as evidenced by the fact they can no longer interbreed.
They can still interbreed, thus they remain the same species.
Islands produce some of the most profound examples of speciation due to geographic isolation.

8. Why does speciation occur after geographical isolation
Why does speciation occur after geographical isolation? Use the anoles as your example

9. Why does speciation occur after geographic isolation?
The population that left the original group will have a different allelic make-up than the original species, thus experiencing the “founder effect”.
The two groups will continue to experience different mutations.
The two groups will now experience different selection pressures due to living in separate and perhaps different environments.

10. How does speciation occur?
Pre-zygotic barriers- before the zygote forms
Post-zygotic barriers- after the zygote forms

11. Prezygotic: Habitat Isolation
Habitat isolation- two species have developed a preference for two different habitats. Even if the species become sympatric, the probability that they will meet and mate is low.
Another example- The dragonflies Progomphus obscurus and Progumphus alachuensis are closely related. In places where their range overlaps, P. obscurus reproduces in streams whereas P. alachuensis reproduces in lakes.
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.
Graphic
Example: Bufo woodhousei and Bufo americanus are two closely related toads. B. woodhousei prefers to reproduce in the quiet water of a stream whereas B. americanus prefers to reproduce in shallow rain-pools. As a result, they remain separate species.

12. Prezygotic: Seasonal Isolation
Seasonal isolation- the two species have developed different times of the year to mate.
Example: There are four species of frogs from the genus, Rana, each of these frogs mates at different times of the year so that if they are sympatric, no interbreeding occurs.
Another example-
Pinus 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.

13. Prezygotic: Behavioral Isolation
Behavioral isolation- If courtship behavior changes during separation, then sympatric mating will not occur and two new species are formed.
Example: Twelve fiddler crab species inhabit a certain beach in Panama. Males of each species have distinctive mating displays which include waving claws, elevating the body, and moving around the burrow.
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.

14. Prezygotic: Mechanical Isolation
Mechanical isolation- There is a physical or biological structure that prevents mating. For example differences in the size or fit of genitalia may not allow mating. This can be found in certain snails, insects and plants.
Example: The Bradybaena shown are two different species of snails because the shells spiral in opposite directions, thus they are unable to mate with one another.

15. Summary of Prezygotic Barriers
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.
When allopatric speciation occurs, usually more than one isolation mechanism also occurs and more than one trait will change between the two populations.

16. Postzygotic: Developmental Isolation
Developmental isolation- If fertilization occurs, the development of 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.
Graphic example-The eggs of fish can be fertilized by other fish species sperm due to external fertilization.
This results in malformed embryos.

17. 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.
occurs after mating species overcome pre-zygotic 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 prevents 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

18. Postzygotic- Hybrid Sterility
Hybrid sterility- some hybrids produce superior offspring but the offspring are sterile.
Example: A mule is the result of female horse crossed with a male donkey. Mules are sterile, thus there is no potential for gene flow. In terms of evolution it is a dead end. The horse is on the left, the donkey is in the center and the mule is on the right.
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 burrow is a feral donkey. A mule is the offspring of a male (jack) donkey and a female horse. A hinny is the offspring of a cross between a female donkey and a male horse and are rare.

19. 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 are allopatric and changes occur, most likely more than one of the 10 barriers will occur in the population leading to speciation.

20. 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.

21. 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.
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.
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.

22. 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.

23. 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.

24. Exit Ticket (Quick formal grade)
1. Explain one specific example of allopatric speciation occurring (3 points)
2. Explain one specific example of sympatric speciation occurring (3 points)
3. Compare and contrast post zygotic and pre zygotic barriers (3 points)
4. Using the lizards from last class, explain how speciation occurred. (11 points)