Stimulating Understanding of Computational science through Collaboration, Exploration, Experiment, and Discovery for students with Hearing Impairments
a collaboration of the Shodor Education Foundation, Inc., Eastern North Carolina School for the Deaf, Barton College, the National Technical Institute for the Deaf, and Interpreters, Inc.

For Teachers!

A note to teachers

The Effect of Medications on Daphnia

This page walks you through the student pages "What does the model look like?" and "What experiment can I do with the
model?" 

The student questions are in red. The answers are provided on this page in blue. 

Background

This lesson allows the students to simulate a series of experiments designed to evaluate the effect that the trace amounts of medications found in rivers have on daphnia.

Researchers in Minnesota caught carp and walleyes in the effluent of a sewage-treatment plant. Other studies have shown that this type of facility can release estrogenic pollutants. The male fish were producing an egg-yolk protein called vitellogenin. Normally this protein is only produced by female fish. There is speculation that the inability of some male fish to make sperm is caused by this feminization. Several studies have found a wide range of pharmaceuticals in rivers and lakes.

An experiment designed to test the effect of these drugs on fish would take years and a lot of equipment. Environmental scientists often use daphnia as a quick preliminary check. Daphnia are small (the size of a sesame seed), easily raised animals with a quick life cycle. Females produce a new brood every 2 days. Juveniles reach reproductive age in about 8 days. Daphnia are also very sensitive to pollutants. Students can monitor the effect of drugs like nicotine and caffeine on a daphnia's heart rate. With a few weeks and a room of jars, a scientist can probe the effect of dozens of chemicals on daphnia. If the daphnia respond negatively, then more involved experiments can be justified. 

Colleen Flaherty, a MS student at the University of Wisconsin-Madison, undertook this task. She made water with the same trace concentrations of these medications that are found in lakes and rivers. Then she raised daphnia in the water. Some daphnia had only one medication whileothers had combinations of drugs. In each trial she monitored the development of one female daphnia and all of its broods.

In general she found that a single medication had a minor effect. Sometimes after an initial drop in productivity the daphnia became acclimated and returned to normal or even above normal productivity. Combining medications was another story. For example when the cholesterol-lowering drug Clofibric acid combined with the antidepressant fluoxetine there was a 90% mortality rate. 

This is a relatively quick and simple experiment for a university laboratory, but it goes beyond the time that most middle or high school science classes can devote. This lesson uses a computer model of daphnia to simulate the pharmaceuticals effect. In a few minutes the students will have simulated the experiments and will have data that they can analyze. 

The model is written in STELLA. STELLA is designed around flowchart icons. Double clicking an icon opens it so you can see the mathematical operation it performs. Even without looking at the math the students can get a general understanding of the model by following the flowchart. The red arrows share information so a calculation can be performed.

Notes and answers to student questions.

Run the model and see how the daphnia reproduce when there is no medication in the water.

1) Describe how the male and female populations change. What are their highest and lowest numbers?

The male population starts at a high of 1 and slowly and steadily falls to .41.The average decrease is 3.02% per day. The female population increased from 1 to 11,178.79. The increase averaged 21.4% each day .See Excel spreadsheet "data_analysis."


Click on the fluoxetine button. The center should be green. This adds a small amount of the antidepressant fluoxetine
to the water. Run the model again to see how the daphnia grow with this medication.


2) Describe how the male and female populations change with fluoxetine in the water. What are their highest and
lowest numbers? The fluoxetine didn't have an effect on the male population. The male population moved from 1 to .41. The female population did a little better. It rose to a high of 11,333.31 an increase of 154.52 over the control.


Click on the fluoxetine button again to remove it from the water. The fluoxetine button should be gray not green.
Click on the clofibric button to add it to the water. Run the model to see how the daphnia grow with this medication.


3) Describe how the male and female populations change with clofibric in the water. What are their highest and
lowest numbers? The male population increased to 40.44, an average increase of 10.4% per day. The numbers of male are still small compared to the total daphnia population but it is a significant difference for the male population. The female population rose to 10,695.26 or 483.53 less than the control.  


4) Predict what will happen when you add both fluoxetine and clofibric acid to the daphnia's water. Answers will vary.


For the last trial add both fluoxetine and clofibric to the water. Both buttons should be green. Run the model.


5) Describe how the male and female populations change with both fluoxetine and clofibric in the water. What
are their highest and lowest numbers? The male dies and the females increase in number very slowly. There is a slow increase from generation to generation but the 90% mortality rate keeps the increase in check. The male population goes from 1 to 0. The female population goes from 1 to 98.09.


Copy the data from the tables to a spreadsheet. Design an algorithm to compare the control run with each of
the runs with medication. (Hint: subtracting the control number from the medicated number will give the
difference for each day.)


6) Describe the short- and long- term effect of the two medications on your daphnia. 
In the female analysis and male analysis spreadsheets, columns G, I and K calculate the drug population - the control. This tells us the difference in the effects of the medication. The Fluoxetine had no observable effect until day 20 for the females. From there on we see a modest increase in the number of females (154.52 more at day 30). Fluoxetine had no observable effect on the male population. Clofibric acid had no initial effect on the female population. After day 9 there is a small decrease in the rate of growth resulting in 483.53 fewer females at day 30. This is a .11% lower average growth rate than the control. The male population starts to rise on day 2. By day 30 there is an increase of 40.03 males. This is a small proportion of the total daphnia population but dramatic for the male population. The male population reached a high of 45.99 on day 25 and then decreased to 40.44 on day 30.

7) Describe the effect on the daphnia with both medications in the water. From day 1 there is a significant reduction in both the male and female population. By the third day the male population is reduced to 0. It never recovers. The female population increases, but very slowly, with only 98.09 females at day 30. This is 11,080.7 fewer females at day 30 or .88% of the control population.


8) Would you recommend additional experiments to see if medications affect other animals in rivers and streams? Defend your recommendation. Answers will vary. Look for logical arguments and evidence to support the arguments.

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This project is supported, in part, by the National Science Foundation Opinions expressed are those of the authors and not necessarily those of the National Science Foundation.