7 Guiding Question Two

If there is a difference in the frequency of deformed frogs in Top Pond versus Bottom Pond, then what is its cause?

Possible answers include:

  • Hypothesis 1: The deformities are caused by the worms, and one pond has more worms than the other. That is, the variation in number of legs is environmental—and genes are irrelevant.
  • Hypothesis 2: The frogs in one pond are, on average, inherently more prone to deformity than the frogs in the other. That is, the variation in number of legs is genetic—and worms are irrelevant.

For more details (and other possible answers), see Chapter 3 - Kinds of Variation.

Your job is to design and conduct studies that will reveal which answer is correct.

Your studies can be observational or experimental. Here are some things you might do:

  • Examine the frogs, and classify and count them. The tanks will be helpful here. For example, you might examine frogs from Top Pond, put the five-legged individuals in Tank 1 and the four-legged individuals in Tank 2, then further sort the frogs in each tank by whether or not they are infected with worms. Does the hypothesis you are testing explain any associations you discover (or lack of associations)?

  • Move frogs (and, if you like, worms) from the ponds to the smaller tanks. Run the simulation for a couple of generations. Then classify and count the frogs in your tanks. Does the hypotheses you are testing allow you to accurately predict when you’ll end up with a high (or low) frequency of five-legged frogs?

  • Mate particular frogs with each other. Move two frogs to a tank. Encourage them to mate by making sure they are touching each other.

    Screenshot from FrogPond application. The user has put a pair of frogs together in a tank, one on top of the other.
    To encourage a pair of frogs to mate, introduce them to each other.

    Run the simulation for a short time. You will see the parents make tadpoles. Let the tadpoles grow up, then examine them. Does the hypotheses you are testing allow you to accurately predict when you’ll end up with a high (or low) frequency of five-legged frogs?

  • Get rid of particular frogs (or worms) by dragging them out of a pond or tank. Then run the simulation. Does the hypotheses you are testing allow you to accurately predict how the frequency of five-legged frogs will change?

You will have noticed that I have only told you pieces of what you might do during your studies. I haven’t told exactly what study designs to carry out. That is up to you. I will, however, offer these pieces of general advice:

  • An effective way to proceed is to pick one of the possible answers as your working hypothesis. I suggest you start by investigating Hypothesis 1. Then do something with the frogs. Predict what will happen if your hypothesis is right, and what will happen if it is wrong. Collect data and analyze it—with a graph or a table—to see what actually happened.

  • You may have to repeat a study a few times before a clear pattern emerges in the data.

  • If your study still does not produce a clear outcome, try something different.

I encourage you to spend some time working out study designs without additional hints. Collaborate with a classmate.

  1. Which hypothesis will you investigate first?

  2. Describe and diagram a study that will test the hypothesis you have chosen.

  3. Run your study. Describe and diagram your results. Was your hypothesis correct? If not, design and run a study to test another hypothesis.

  4. What can you conclude about the cause of deformity?

If you need more suggestions on kinds of studies you can run, see Appendix B - Study Designs.