Evolution Package 

Speciation Worksheet

Powerpoint: Feb 5

• Explain how new species arise in response to new niches
• Differentiate among and give examples of convergent evolution, divergent evolution (or adaptive radiation) and speciation.

Speciation: occurs when a population diverges and begins to evolve into different species.

Speciation can occur via any number of evolutionary mechanisms. All the mechanisms operate at different times, different places and with different intensity to produce new species.

Species: A distinct, identifiable group of populations whose members can interbreed. Generally distinct from other species in appearance, behaviour, habitat, ecology, genetic characteristics and etc.

Niches: The particular habitat requirements of a certain species and the role that species plays in the ecosystem

The important thing to know about niches is that they represent an environment (food, abiotic factors, predators etc.) that can then lead to the evolution of new species. Recall that in the case of natural selection, the environment impacts the evolution of species. In the population, where there are a variety of traits, some traits will be better adapted for survival and reproduction. These traits (and the alleles associated with them) will be selected for and likely increase in frequency.

Genetic drift and a lack of gene flow can also contribute to speciation. Genetic drift (founder effect) leads to the geographic isolation of species. The geographic isolation of the species reduces gene flow (exchange of alleles via mating) in the old and new population. Therefore, the differences between the populations can continue.

Let’s take a look at an example:

On the island of Anguilla, an isolated island thousands of miles away from any form of land, researchers found populations of iguanas. They noticed that the iguanas existed in two distinct populations, one lived on land (mainland iguanas) and the second lived in and next to the sea (marine iguanas). The researchers hypothesized that the two types of iguana are descended from the green iguanas of South America, and must have been blown out to sea from South America during the storms and established at Anguilla. 

Given your knowledge of evolution, how did the two types of iguana (mainland and marine) arise from the original Green iguana population?

As with any case in speciation, there are multiple possible evolutionary forces that could have contributed to it. Here is one way that it may have happened:

• Genetic Drift (founder effect): The green iguanas that were shipwrecked on Anguilla were probably genetically and maybe morphologically different from their counterparts in South America. Therefore, the allele frequencies has already changed and evolution has happened, though that alone would not make a new species.
• Natural Selection: Natural selection occurs where species that are unable to adapt to the environment (or their niche) are less likely to survive and reproduce. In this case, however, there may have been two very different niches for the iguanas to adapt to: the marine one and land one. Therefore, some green iguanas who were able to adapt to land were more successful, while the ones who adapted to the sea were more successful. Each population began to adapt to their respective environments.
• Gene Flow (LACK OF GENE FLOW): Because the iguana populations were geographically distinct, they may have not interacted as much. Therefore, gene flow was reduced and exchange of alleles would reduce. The genetic (and morphological) differences between the two populations increase and the two diverge.
• Mutations: mutations will always play a role in adding new traits to a population. However, since the iguanas are in a different environment, different traits will give the iguanas different success. As a simplified example, if a mutation in the marine iguana population were to cause them to be able to stay under the water for longer periods of time, the trait would be very beneficial. The trait would then lead to the successful survival and reproduction of the individuals who have it and become increasingly common in the population. Such a trait may not be as useful in the land iguanas and may not be selected for.

Please note that the scenarios are NOT representative of what you will see on the test. The scenarios are for you to think more deeply about natural phenomenon and critically think about the mechanisms of evolution.

Handouts: 

Scenario Activity – Speciation – DOES NOT represent the test. For thinking more deeply about natural phenomenon.

Speciation – Review Worksheet (finish for Wednesday please). It’s a short one 🙂

Powerpoint: Feb 4

Learning Objectives

• Explain random fluctuations in genes may produce changes in genetic frequency
• Describe how the size of the population may reduce genetic diversity
• Describe how mutations introduce new traits into a population
• Explain why mutations are most likely to establish in large populations

And because I was half asleep when I wrote these learning objectives I’m going to rewrite them in a way that’s more understandable.

• Explain how genetic drift can produce changes in genetic frequency (evolution)
• Describe how allele frequencies fluctuate more dramatically in smaller populations than larger ones
• Describe how genetic drift tends to decrease genetic diversity
• Define the bottleneck effect and founder effect
• Describe how mutations introduce new alleles (and sometimes traits) into a population

Genetic drift is defined as random fluctuations (changes) in genetic frequency due to chance events. This is also known as sampling error (when the sample of the population does not represent the diversity of the population). To picture this, imagine a bag with 5 pokeballs, 15 ultra balls and 30 master balls.

Suppose you were to draw 10 balls out of the bag. There is only one way you could draw the balls in order to have a sub-population that is representative of the original (1 pokeball, 3 ultra ball and 6 master balls). In a natural population of organisms, where each organism has hundreds of genes and each gene may have many more alleles, the probability that you will draw a population that is exactly representative of the population is next to none.

There are two types of genetic drift: bottleneck effect and founder effect.

Bottleneck effect: The bottleneck effect occurs when the population is suddenly heavily reduced. The remaining individuals in the population are unlikely to be an exact representative of the original, meaning, allele frequencies has changed. Therefore, evolution has occurred, simply because the allele frequencies has changed.

The causes of bottleneck effects vary. Natural disasters, human factors and natural boom and bust in the population (for example, algae blooms and locusts, which naturally increase and decrease in number drastically in cycles) can all cause a sudden and dramatic reduction in the population.

Founder effect: occurs when members of one population “splits off” from the original population and founds their own population. Again, the sample is unlikely to exactly reflect the allele frequency of the original.

An example of a founder effect can be seen in human migration. When Europeans left the continent of Europe to travel to North America, the population that left Europe is unlikely to exactly reflect or properly represent the population of Europe.

Genetic drift is more pronounced in a small population than a large one. Let’s use the fuzzy buns as an example. If we had a population of 200 fuzzy buns, a total of 400 alleles (since each fuzzy bun has 2 copies of DNA), and one of the fuzzy buns died, that is a loss of 2 of 400 (0.5%) of the alleles in the population. However, if the population numbered just 2, a loss of one fuzzy bun is a loss of 2 of 4 of the alleles, which equates to a 50% drop in the alleles of the population.

In the case of Genetic drift, the genetic diversity can only stay the same or decrease. Since no new alleles are being made, the reduced population is more likely to have far less alleles than the original. Going back to our poke-ball example, if we drew out a few of the balls, we can only have a genetic diversity that is equal (we draw out a master ball, a poke ball and an ultra ball) or less than the original. We can’t draw out any new “alleles” to increase the diversity (e.g. a safari ball).

Since alleles are more likely to be lost, either due to genetic drift or due to selection against the allele, if no new alleles are added to the population, more and more alleles will be lost over time. Thankfully, mutations help to replenish the diversity by adding new alleles over time.

Pay attention 0:00 to 2:10

Mutation are any changes in the DNA of the organism.

Mutations tend to arise when mistakes are made in repairing a broken piece of DNA. When repair enzymes repair the DNA, they often replace the base pairs with something entirely different, or insert/delete new nitrogenous base pairs in place. In either case, new alleles are formed. This can then lead to changes in the characteristics of the organism (e.g. cancer) or offspring of the organism (albinism or hairlessness).

Since natural selection can only act on traits that are heritable, and only the gametes (egg or sperm cells) of an organism’s body are passed to the next generation (if the organism reproduces sexually), only mutations in the gametes lead to evolutionary change.

If the organism reproduces asexually however, the mutation will be propagated into the next generation.

Handouts

Group Activity – Investigating Genetic Drift

Notes Package – Study Package (Complete by next Wednesday!)

Powerpoint Feb 3

Learning Objectives

• Explain how non-random mating can also “select” for genetic changes in a population
• Explain what stops non-random traits from going “too far”
• Explain how gene flow introduces or excludes genes from a population and changes the gene frequency
• Explain how gene flow can change the genetic diversity of a gene pool

Sexual selection is a mode of natural selection where typically members of one biological sex choose mates of the other sex with whom to mate (intersexual selection)

• e.g. male peacocks and birds of paradise display for the females to try and attract a mate

OR competition between members of the same sex to sexually reproduce with members of the opposite sex (intra-sexual selection).

• e.g. male rams fight for access to females

Sexual selection (or non-random mating) also “selects” for certain alleles and traits in a population. However, unlike natural selection, the selection is not based on increasing the organism’s chances of survival, but increasing the organism’s chance of reproduction. Traits that are selected for should increase the organism’s fitness. The fitness of an organism is the reproductive success of the organism (the number of offspring that survive to reproductive age). Since these “sexual” traits also increase the organism’s chances at reproduction, the traits are selected for.

This is also why these sexual traits do not become too extreme. Sexual traits that are too extreme may increase the reproductive success, but decreases the chances of survival (e.g. a moose with a horn that is too large will likely be less likely to run away from predators, or it will take more energy to make the horns).

Gene Flow (immigration/emmigration) DOES NOT select for certain alleles and traits in a population. It is simply the movement of alleles from one population to the other. When individuals travel from one population to another, they carry the genetic information (alleles) with them, and adds to the existing alleles in the population (and gene pool). Therefore, the genetic diversity of the populations increase.

• e.g. Dandelion seeds scatter into the wind and carry with them their alleles to another population of dandelions
• e.g. Swedish individuals with alleles that code for blonde-hair and blue-eyes move to India and marry into an Indian family. By immigrating to India, and marrying into the population, the family has essentially contributed their genetic information to the Indian population and increased the genetic diversity.

Powerpoint: Feb 2 (updated)

Learning Objectives

• Define evolution
• Describe natural selection and artificial selection
• Identify the criteria for evolutionary change via natural selection
• Describe  how the environment drives evolutionary change
• Explain why genetic/trait diversity is important in a population for evolutionary change

Evolution is defined as changes in the frequency of alleles in a population. As the frequency of alleles change in a population, the physical characteristics (which we see) of the population also change. This is why we often equate evolutionary change with physical change. It is important to note that evolution happens on the molecular level, it does not need to be physical, visible, or apparent. 

• Alleles are the different versions of a gene. (sky blue fur allele/black fur allele)
• Genes are sections of DNA that code for different things. (the section of DNA that coded for Fur/Limbs/Teeth)
• DNA is the molecular blueprint of all living things.

There are five main factors that can cause the frequency of alleles in a population to change. One of them is natural selection. 

• Natural selection occurs when a trait that exists in certain individuals, in a population, allow the individual to have a better change at surviving and reproducing than others without the trait. For example, a finch with a beak slightly larger than his friend will be better able to break open seeds. They are therefore more likely to survive and reproduce.
• In other words, natural selection increases an organism’s fitness (the reproductive success of an organism)
• Watch the introduction of this video for an example of natural selection.

More examples of natural selection:

• Sloths with less muscle are better able to survive and reproduce. A lower muscle mass needs less energy, and since sloths feed on leaves with very little energy, sloths that need less food to survive are more successful and more likely to reproduce.
• Clearwing Moths with pigmentations that resemble a bee are better able to survive and reproduce, since predators that mistake it for a bee will stay away.

It is very important to keep in mind that these traits are not “better” than other traits, they allow the organism to better survive and reproduce than others. The conditions of the environment determines what traits are selected for. For example, the white color was selected for in moths before the industrial revolution. During the industrial revolution, the white color was no longer selected for, since the white color actually made the moth more visible to predators.

Artificial selection is when humans are the ones selecting for traits. An example of this is dog breeding, where certain traits (furry coat, long legs, or small stature if its a chihuahua…) are being selected for. This is very common with animals that are being bred for food, for example, cows that are bred for the quality of their skin, which are used to produce leather for cars.

Genetic and trait diversity is very important in populations. When there are varied traits, there is a greater chance there will be some traits that will allow some individuals to survive. It is like having more tools in your toolkit, there is a good chance that at least one of those tools will work. This is also a tactic used in gambling, called hedge-betting. 

Study tip: 

• All the case studies that we did as an activity in class is in the power point. You can go back to them and study.
• Or, think of an example of natural selection in another organism and make a question
• Pay special attention to the four criteria for natural selection.