SCIN 130 Lab 4: Stickleback Evolution, Part 2

General Instructions

Be sure to read the general instructions from the Lessons portion of the class prior to completing this packet.

Remember, you are to upload this packet with your quiz for the week!


In this experiment, you will analyze the pelvic structures of stickleback fish collected from two lakes around Cook Inlet, Alaska, to determine whether there are significant differences between the two populations. You will then use your data and information about the lakes to draw conclusions about the possible environmental factors affecting the evolution of pelvis morphology.

Specific Lab Instructions



Return to: The Virtual Stickleback Evolution Lab

You are going to perform Experiment 2 for the Stickleback lab this week.

Begin with Tutorial 2. When you are comfortable scoring a pelvis in fossil fish, you may move on (Note: it is a little more difficult in fossils than live fish, so you may want to spend a little time here).

1. What score would you assign to a fossil specimen that has only one pelvic spine visible?

2. A stickleback fossil may show no signs of pelvic structures. What are possible sources of error associated with scoring the pelvis of such a fossil as “absent”?

When you feel you have mastered scoring fossils, you may move on to Experiment 2.

1. In your own words describe the overall objective of Experiment 2 and explain what the data you collect will allow you to estimate.

2. What is one type of information that researchers can gain from studying fossils that they cannot obtain from living populations?

SCIN130 Lab 4: Stickleback Evolution, Part 2

V1 04.2018 Felicetti

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Begin the experiment in the window on the left. Complete Part 1: Preparing Fossils (click on the bench to get started).

3. You will collect data on pelvic structures using fossils from rock layers 2 and 5. Approximately how many years of deposition separate these two layers?

4. Which layer is older, 2 or 5? Explain your answer.

Complete Part 2 of the lab in the window on the left.

Score Your Fossils

5. Based on the pelvic phenotypes you measured, do the fossils in layer 2 differ from those in layer 5? Explain how.

6. After your collect data for the pelvic phenotype in layers 2 and 5, add your totals, and submit. As in lab 3, you may use the graph feature in the program as it works fine, or you can create your own Excel graph. Insert a screenshot here.

7. How do your data compare to those collected by Dr. Bell and colleagues?

8. Take the quiz. What can be inferred about the presence or absence of predatory fish when the Truckee Formation was a lake? Describe the evidence.

9. After completing the quiz, click on Experiment 2 Analysis.


11. Complete the tables below as you perform the rate calculations. (The link to the instructions is very helpful.)

Sample Layer Number of Fish with a Complete Pelvis Total Number of Fish Sampled Relative Frequency of Complete Pelvis Trait in Population Sampled






Time Decrease in Percentage of Complete Pelvis Trait per Thousand Years (Rate of Change)
First 3,000 years (Layer 1 to Layer 2)

Next 3,000 years (Layer 2 to Layer 3)

Next 3,000 years (Layer 3 to Layer 4)

Next 3,000 years (Layer 4 to Layer 5)

Next 3,000 years (Layer 5 to Layer 6)

Total 15,000 years (Layer 1 to Layer 6)

1. What does it mean when the rate of change is a negative number?

2. Complete the Analysis Quiz.

3. Describe the trend in the data over time.

4. Why is it important to calculate the rate of change over time?


6. In what way is the change in the complete pelvis phenotype in the fossils from the Nevada lakebed similar to what might have occurred in Bear Paw Lake from Experiment 1?

Adapted from: Brokaw, A. (2013). Stickleback Evolution Virtual Lab. HHMI Biointeractive Teaching Materials.

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