Queen Essays

10

Mechanisms Driving the Evolution of Fur Color in Mice

Bio 106 Life Sciences

Brightpoint Community College

Objectives:

After this exercise, you should be able to:

· Collect and analyze data from a simulation to explain how predation affects the numbers and/or distributions of organisms in an environment.

· Construct an explanation based on evidence for how natural selection leads to adaptations of populations.

· Evaluate the evidence supporting claims that changes in environmental conditions may lead to evolution.

· Discuss the role of mutation as a mechanism of evolution.

Introduction

Deer mice are a species of mice that live in North America. Deer mice that can effectively match their appearances to their surroundings become to live in many different environments. There are many different types or subspecies of deer mouse. A subspecies is a population within a species that forms its own group and takes on some new characteristics. These deer mouse subspecies can be found all across North America, from the East Coast to the West Coast, and from the Gulf of Mexico to the Arctic Circle. On the map of North America to the right (Figure 1), the shaded areas show where deer mice live. Each color represents a different subspecies of deer mouse.

Figure 1: Range of Deer Mice in the US. Each color represents a subspecies.

Figure 2: Variety of fur colors for Deer Mice

All the mice in these photos are deer mice, but they live in different environments and have different fur colors (Figure 2). (Images modified from  Bedford, N. L., & Hoekstra, H. E. (2015). The natural history of model organisms: Peromyscus mice as a model for studying natural variation. Elife, 4, e06813 .).

Mice that can effectively match their appearance to their surroundings become less visible to hawks and other predators. For instance, a dark-colored mouse would stand out more to a predator in light-colored environments like sandy fields, while a light-colored mouse would face greater risks in dark-colored settings like wooded fields. Consequently, the ability of mice to camouflage themselves in response to their environment plays a role in their survival. By blending in, they enhance their odds of staying hidden and reducing their chances of being spotted by predators.

The process of evolution is driven by mechanisms like natural selection. Evolution is defined as a change in the frequency of alleles or genotypes within a population over time. Studying evolution at the population level allows scientists to observe and analyze how various selective pressures, such as those influencing fur colors in deer mice, impact the distribution of the genes that code for these traits. By studying how predators sort a population, researchers gain a deeper understanding of the specific environmental factors driving the development and maintenance of fur colors. This knowledge can also provide insights into the broader biodiversity and adaptive strategies exhibited by other species in response to their environments.

Activity 1: Factors that Determine Deer Mice Fur Color

You will use a simulation that mimics both light-colored and dark-colored habitats. The simulation will allow you to observe and analyze the behavior of deer mice in response to the presence of predators in these different environments. By comparing the population dynamics and survival rates of deer mice in light-colored and dark-colored habitats with and without predators, you can gain insights into how fur color affects their vulnerability to predation and how natural selection works.

Materials:

· Computer

Procedure:

1. Open the Simulation: https://learn.concord.org/eresources/1701.run_resource_html

2. Click on Lesson 1.2 Ecology.

Page 1 of the Simulation

3. You should be on the home page of the assignment. Your next step is to click on Number 1 at the bottom of the page to go to Page 1. Learn more about using the simulation. Tip: Run this simulation on a computer and make the page full screen.

a. Start exploring by clicking the Run button at the bottom of the screen. Observe what happens when you click the run button and then pause.

b. Click the Add button. What happens when you click the add button and then remove?

c. Click the Field Change button. What happens when you click the field and then beach button?

d. Click the Inspect button and then roll your cursor over a mouse and click on the mouse you selected. What comes up the far-right window? Click the inspect button again to toggle it off.

e. Click the Collect button then scroll over and click on a mouse. What pops up in the blue sample window on the far left? Click the collect button again to toggle it off. You will not use this button during this simulation.

f. Click the Reset button. This will reset the simulation back to the beginning.

g. In the far-right window at the top, click the graph button. It is the middle button at the top of the orange window (Figure 3).

Figure 3: Location of the graph button.

When you click the graph button, a graph will pop up in the Data screen to the right of the mice.

h. Click the run button again, let the simulation run for 12 months and then hit pause to stop it. Observe the graph that is created (Figure 4). The graph tracks the number of mice that are light brown, medium brown, and dark brown. The genetics engine underlying this simulation uses principles of genetics including random assortment of chromosomes, diploidy, meiosis, realistic lifespan, etc. As a result, there will be numerical differences between Figure 4 and your results that are true to real-world genetics, based on chance occurrences. In other words, no two graphs will look alike.

Figure 4 Number of mice by fur color in population after twelve months

LAB DATA 1. Take a screen shot of your population graph at 12 months and paste below:

i. Click the Inspect button and click on a Dark brown mouse, a medium brown mouse, and a light brown mouse. Click the inspect button again toggle it off. Note their genotype below.

Question 1. Fill in the genotypes for each phenotype (fur color) or the mice. Double click on the “_______” and replace with the genotype.

· Light Brown Genotype: _______

· Medium Brown Genotype: ______

· Dark Brown Genotype: _______

j. Click on the graph icon (located in the upper left of the far-right window) to go back to the graph.

k. Click on the pie chart icon in the upper left of the far-right window. The data will be converted to a pie chart (See Figure 5).

A pie chart (or pie graph) is a pictorial representation of the data that uses "pie slices" to show relative sizes of data. For this chart, each slice of the pie shows the relative frequency of mice for a given fur color in the population at that point in time.

Figure 5: Pie Chart showing the relative frequencies of fur color in the population initially and at 60 months.

Due to incomplete dominance, the three fur colors are coded for by three different genotypes. Thus, the frequency of the fur color is also the frequency of the corresponding genotype in the population. For example, Figure 5 lists frequency of mice with dark-brown fur at 33% initially. Since mice with brown fur are always the genotype RDRD, the frequency of this genotype in the population is also 33%.

Question 2. In this simulation, the frequency of the fur color is equal to the frequency of the corresponding genotype in the population. Using the pie chart in Figure 5, what is the genotype frequency at 60 months for each fur color? Hint: Genotype Frequency = Frequency of fur color.

· RDRD (Dark Brown):

· RDRL (Medium Brown):

· RLRL (Light Brown)

Evolution is defined as the allele or gene frequencies in the population over time. Look at Figure 5, you can clearly see that the genotypic frequencies changed over time, 0 months compared to 12 months. We can say with certainty that the population has evolved in those 12 months. Please keep in mind, while we can say for certainty the population has evolved, it will take further investigation to determine the causative factor (natural selection, mutation, genetic drift, and/or gene flow).

LAB DATA 2. Go back to the simulation and take a screen shot of your pie chart and insert it below.

Question 3. Look at the pie graphs and compare the frequencies at time 0 and at 12 months. Did the population evolve? Explain how you reached your conclusion.

Question 4. Page 1, Question #1: After playing around with the simulation and getting comfortable with the controls, start to make observations and write them below. Here is an example observation to get you started: When you run the simulation, the mice move around the environment.

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Page 2 of the Simulation

4. Look at the bottom of the window and click on the number 2 to move on to Page 2 of the simulation. It is time to collect and analyze some data to help determine what influences fur color in deer mice. Read the Instructions in the simulation below to set up and run experiments.

5. Run the simulation with mice in the field for 60 months with Hawks.

a. Click on the graph button before you begin the simulation. The graph button is located in the upper right corner of the Data window. The graph button is the middle button with an arrow.

b. Click the Add button to add hawks to the population.

c. Click the Run button and let the simulation for 60 months the hit pause. You can watch the months tick off on the x-axis of the graph.

d. Once you have stopped the simulation at 60 months, place your cursor over data point at 60 months to get the exact number of mice (Figure 6). Record the number of mice under the column, Trial 1 in Table 2 on the next page.

Figure 6:Number of Mice at 60 months

e. After you screenshot the number of Mice for Trial 1, hit the Show All Data button, and save a screen shot of your graph. You will insert the and label the picture to indicate trial number (1, 2 or 3) in Lab Data Question 3 on the next page.

f. In Table 2 below, calculate the Average Number of Mice and Average Percentage of Mice in the Population at 60 months. Note: Hopefully, you noticed the frequent mouse births and deaths over the course of 5 years. It is important to realize that there are many generations of mice over this five-year period. It is critical that you understand that many generations of mice are passing by as the fur color of the population changes because evolution is a change in gene frequencies over generations. You can measure this indirectly by measuring the phenotypic frequencies of the mice from the initial start to the end of five years (60 months).

g. Hit the reset button and repeat these for two more trials for a total of three trials.

6. Reset the simulation then click on the Environment button and change environment to Beach. Repeat steps 5A-F for the beach environment. Record data in Table 2. Paste Screen shots of each graph on

LAB DATA 3. Field with Hawks. Insert graphs. Label each as Trial 1, Trial 2, and Trial 3.

LAB DATA 4. Beach with Hawks Insert graphs. Label each as Trial 1, Trial 2, and Trial 3.

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2 | Page

LAB DATA 6. Page 2, Question 2. Type your answer in the box and then copy and paste it here. Describe how the numbers of dark, medium, and light-colored mice change in the population over a single trial.

LAB DATA 7. Page 2, Question 3. Type your answer in the box and then copy and paste it here. Compare the average percentages at the end of the trials with the percentages from the beginning. The population always starts with approximately 33% of each color.

· Field Environment

· Initial Frequency of all equal ~33.3%

· List the frequency at 60 months:

· Light Fur:

· Medium Fur:

· Dark Fur:

· How did the frequencies change over time?

· Beach Environment

· Initial Frequency of all equal ~33.3%

· List the frequency at 60 months:

· Light Fur:

· Medium Fur:

· Dark Fur:

· How did the frequencies change over time?

Question 5. Based on your data, do you think the hawk acting as a predator sorted the population?

Question 6. The frequency of the fur colors is also frequency of the corresponding genotype in the population. If evolution is defined as a change in allele or genotype frequency over generations in a population, did this population evolve? Explain how you reached your conclusion.

Question 7. There are four main mechanisms of evolution: natural selection, mutation, genetic drift, and gene flow. Review these four mechanisms in your textbook and then determine which of the four were at work in this simulation.

Page 3 of Simulation:

7. Click on number 3 to move on to Page 3 of the simulation. Hawks are predatory birds that use sight to catch their prey. It is clear from the previous experiment that when hawks are present, they prey more on mice that do not blend in with the environment. In this simulation, you will redo your experiments from before, except this time, you will investigate what happens in the population when there are no hawks present.

LAB DATA 8. Page 3, Question 4. Before trying the simulation, write a prediction for how the numbers of mice with different colors will change when there is no predator. For example: When the environment is light (beach), the number of dark, medium, and light mice at the end of the trial will be ……

8. Run the simulation with mice on the beach for 60 months with No Hawks.

a. Click on the graph button before you begin the simulation.

b. Double check that the environment is the field. Click the Change button if you need to switch.

c. Add hawks and run the simulation for 60 months the hit pause.

d. Roll your cursor over a line on the graph at 60 months and record the number of mice under the column, Trial 1 in Table 3.

Figure 7 How to View the Number of Mice at 60 months

e. After you have recorded the number of Mice for Trial 1, hit the Show all Data button, and save a screen shot of your graph. You will insert the and label the picture to indicate trial number (1, 2 or 3) in Lab Data Question 4 on the next page.

f. In Table 3 below, calculate the Average Number of Mice and Average Percentage of Mice in the Population at 60 months.

g. Hit the reset button and repeat these for two more trials for a total of three trials.

9. Reset the simulation then click on the Environment button and change environment to Beach with No Hawks. Repeat steps 8A-F for the beach environment. Record data in Table 3 on the next page. Insert a screen shot of the three graphs in Lab Data Question 9 below.

LAB DATA 9. Insert the three graphs for the field here:

LAB DATA 10. Insert the three graphs for the beach here:

LAB DATA 12. Page 3, Queston 5: Compare the average percentages at the end of the trials with the percentages from the beginning for each environment. (The population started with approximately 33 percent of each color.) What were the final average percentages in the beach environment for each of the different colors?

LAB DATA 13. Page 3, Question 5: In the field environment, what were the final average percentages for each of the different fur colors?

Question 8. In this simulation, the frequencies of the fur color equal the genetic frequencies in this population because each genotype codes for a unique fur color. Evolution is defined as a change in gene or allele frequencies over time. Did the population evolve?

The inheritance pattern for fur color in this simulation is incomplete dominance, hence the three fur color phenotypes. Without a predator, medium brown will usually (though not always) become the most common fur color in the population over 60 months, increasing from about 33% at the start, to around 50%. Even without a predator, the population continues to change. The change in gene frequencies is random.

Question 9. There are four main mechanisms of evolution: natural selection, mutation, genetic drift, and gene flow. Review these four mechanisms in your textbook and then determine which of the four were at work in this simulation.

Page 4: Creating a Model.

10. Skip this page and continue to page 5. Do not create a model for evolution.

Page 5: Next Steps:

11. You have started to figure out why deer mice have different colored fur in different environments, but there is still more to investigate. However exciting as that discovery would be, we will not continue to do so in this class. Please speculate on an answer for the two following questions.

LAB DATA 14. Page 5, Question 9: What else do you think influences the deer mouse fur color?

LAB DATA 15. Page 5, Question 10, How could you investigate those factors?

12. Continue to the next page by clicking on the orange box. This verifies that you did the experiment. Failure to submit will result in a zero on this portion of the assignment.

LAB DATA 16. Take a screen shot of the Summary of Work with check marks. If you are missing any checks, paste your answers into the boxes on pages 1-3. You skipped page 4 and question #7 in the simulation so it will not have a check mark.

Paste it here:

Activity II: Interactive Assessment for Natural Selection and Adaption

Watch the video, Natural Selection and the Rock Pocket Mouse.

This film uses the rock pocket mouse as a living example of Darwin’s process of natural selection. It highlights the research of Michael Nachman, who has quantified predation on rock pocket mice and identified adaptive changes in coat-color genes that allow the mice to travel under the radar of hungry predators.

The film has embedded questions containing automatic pause points, during which you answer questions about the film to assess your understanding of the concepts presented. After answering all the questions, you can view and save the PDF with your name on it. You may watch the video as many times as you want to earn full credit.  

Question 10. Upload the PDF from the Rock Pocket Mouse Video for full credit.

Question 11. Upload the lab data sheet.

LAB DATA 13. Page 3, Question 5: Refer to Table 3 In the field environment, what were the final average percentages for each of the different fur colors?

Did this match your prediction (refer back to LDQ 8 for your prediction)? Why?