MODERN THEORY OF EVOLUTION – Mechanism of Evolution and SpeciationPART A: Mechanisms of EvolutionFor each scenario below, determine which graph shown, best depicts the situation. [6]

1. A large valley is flooded and a population of lizards is separated. Over time, they travel in opposite directions to two different places and eventually become so different they can no longer interbreed.

Graph:

Explanation:

2. In a population of wheat, variation is the height of the wheat decreases over time.

Graph:

Explanation:

3. In a population of field mice, there are many variations of brown, ranging from a very light brown to a very dark brown. The population becomes more of a medium-brown over time as individuals that best blend in to their surroundings are favored.

Graph:

Explanation:

4. For each scenario, determine the type of natural selection occurring. Be sure to explain the reasons for your choice.

Scenario Selection Type [5](stabilizing, directional or

disruptive)

Rationale [10](explain the reason for your choice, in

detail, in your own words)A population of arctic hares burrow into the snow for shelter. It is found that the hares on the smaller side are also able to burrow between rocks, which provides them extra protection from predators. Over time, the hare population becomes smaller in size.Limpets are a small species that can often be found on the seashore. They come in three variations: dark, light and intermediate. The dark and light colours are easier for sea gulls to spot, and therefore, they are more commonly hunted.If there was a great flood and lemurs that had longer tails were better able to climb and live in trees, while the other phenotypes were not able to survive as well, which type of selection would this be?

In a population of spiders that were hunted by sparrows the large spiders were easy to spot but moved very quickly. The smallest spiders were not very easy to spot. The average size spiders were easier to spot than the small ones but moved more slowly than the large ones, thus making them the most hunted. Which type of selection would this be?In a wild leopard population, cubs that are born with low birth weights lose heat more quickly and tend to die while babies that are too large are not able to deliver through the pelvic bones of the mother leopard. This leads to a high mortality rate for cubs that are born too small or too large.

Some individuals living in parts of the tropics (notably West and Central Africa) suffer from sickle cell anemia. Because they have deformed (sickled) red blood cells, their blood cannot properly transport oxygen. Sickle cell anemia is determined by two alleles, A and S. People who have the AA genotype have normal red blood cells. Those that have the SS genotype develop extreme sickle cell anemia and normally die before puberty. Heterozygous (AS) people have both normal and sicikled red blood cells, and experience mild anemia.The distribution of the sickle cell trait correlates with that of malaria, a parasitic disease carried and spread by mosquitoes. (see maps). Some degree of sickling can kill the malarial parasite. Heterozygotes (AS) contract malaria less frequently than homozygotes (AA).

5. What genotype is advantageous where malaria is prevalent? Why? [2]

6. What type of natural selection is acting on these populations? Explain. [2]

7. In areas where malaria is prevalent, the homozygous AA and SS genotypes are disadvantageous – one leaves you susceptible to malaria and the other gives you sickle cell anemia. If both genotypes are selected against, why do they exist in high frequencies in these populations? [Hint – you may have to use the knowledge you gained in the genetics unit to help explain] [3]

8. For each scenario, determine the mechanisms of evolution it describes: Mutation – either neutral, harmful, or beneficial Natural selection – either stabilizing, directional, or disruptive Non-random mating – either sexual dimorphism, female mate choice, or male-male competition Gene flow – either immigration or emigration Genetic drift – either bottleneck or Founders effect.

Scenario Mechanism of Evolution [9]

(be specific)

Rationale [18](explain the reason for your choice, in

detail, in your own words)When Christopher Columbus sailed to the Americas, he randomly chose 3 chickens from Spain to bring along. These 3 chickens were the only chickens to breed in the Americas for hundreds of years.Scorpions are normally born with one stinger. This scorpion was born with two stingers.

In 2013, Typhoon Haiyan is estimated to have killed over 500 water buffalo in the Philippines. Water buffalo are used in the Philippines to plow crops. Many of the water buffalo that perished were concentrated near farms. These animals are more muscular than buffalo allowed to roam free.Female angler fish measure about a foot in length, while males barely reach half an inch. In some species, the males are not even capable of feeding themselves. Instead, they must quickly find a female to attach themselves to or die. After attaching, their circulatory systems merge and she provides him with sustenance, while he provides her with sperm.

Camouflage allows many species to blend into their environment. Those individuals with the best camouflage are not eaten by predators as often as those with poorer camouflage.

Tree frogs are normally a bright green colour. This tree frog has been born with a gene for albinism.

During a hike a man accidentally and tragically steps on a population of rare beetles that were in the path, leaving just four from the original twenty

When male lions reach the age of two or three, they will often be chased out of the pride by a larger, more dominant male.

A population of flowers on one side of a river transports pollen to the flowers on the other side of the river, producing offspring.

PART B: SPECIATION1. For the following sets of organisms (on the next page), read the information on each card and decide whether you think the

organisms described are the same or different species, or somewhere in between. Look for key species information such as: Do they interbreed? Do they live in the same habitat? Do they have different heritable traits? Are there differences in their DNA?

Once you are done, place the organisms in their appropriate line along a continuum (if you are completing this in a word document, you can create a text box and place it in the appropriate spot along the continuum (one is done for you) [7]:

Explanation: Be specific about the rationale for your choice, and in your own words (one is done for you). [8]:

Salmon and Goldfish – have different habitats, do not interbreed, different heritable traits (anatomy and behaviours).

Salmon and

Goldfish

2. For each scenario, determine the reproductive isolating mechanisms is describes: Pre-zygotic – either behavioural isolation, temporal isolation, ecological/habitat isolation, mechanical isolation, or gametic

isolation. Post-zygotic – zygotic mortality, hybrid inviability, or hybrid infertility.

Scenario Reproductive Isolating Mechanism [8]

(be specific)

Rationale [8](explain the reason for your choice, in

detail, in your own words)The western and eastern meadowlark are very similar in appearance. They do have regions where the two species ranges overlap but very little interspecies mating takes place because of the differences in their songs.

Two species of North American garter snakes – the common garter snake (Thanmophis sirtalis) and the northwest garter snake (Thamnophis ordinoides) live in the same area. However, the northwest garter snake prefers open areas such as meadows and rarely enters water. The common garter snake, on the other hand, is commonly found near water.

Hybrid embryos between sheep and goats die in early development before birth.

Leopard frogs were once believed to be a single, extremely variable species that ranged across North America. Analysing frog calls provided one of the clues that led biologists to realize that there was more than one species of leopard frog. Today, scientists now recognize at least 8 different but related species which all have different mating calls.

Two species of grass plants flower at different times of year, but they live in the same habitat.

In two species of sage, the flowers have different arrangements of male and female reproductive structures. One species is pollinated by bees that carry pollen on their backs, and the other species is pollinated by bees that carry pollen on their wings. If the “wrong” pollinator visits a flower, pollination cannot occur because the pollen does not come into contact with the male structure of the other species.A mule is the offspring of a horse and a donkey. Mules are not able to reproduce.

Different species of cotton plants produce fertile hybrids, but the offspring of the hybrids die as seeds or in early development.

3. Speciation events are triggered by interruptions in gene flow. Distinguish between allopatric speciation and sympatric speciation. Include an example. [4]

4. What type of speciation is caused by a formidable barrier such as the Grand Canyon? Explain. [2]

5. Approximately 3 million years ago the Isthmus of Panama closed, separating the snapping shrimp. How is the example of the snapping shrimp an example of allopatric speciation? [2]

6. Sympatric speciation occurs in populations that live in the same geographic area. How is this possible? [2]