Preface

FrogPond lets you practice designing and running studies to determine the cause(s) of variation among individuals in a model population.

The population you will study is fictitious, but loosely based on a true story. Some years ago, in a variety of places in North America, school children, biologists, and ordinary people discovered populations of frogs with high frequencies of startling deformities—including extra legs.

Photo of a Pacific chorus frog with an extra pair of hind legs. The extra legs appear to sprout from the frog's left hip. They are long and skinny and drag behind the frog.
A Pacific chorus frog with extra legs. From Figure 1 in Goodman and Johnson 2011.

The suspected causes of deformity, some incriminated by stronger evidence than others, included: UV radiation; water pollution; and a parasitic trematode worm, called Ribeiroia, whose larvae can encyst in the tissues of tadpoles and disrupt their development.

Imagine that Amphibians Unlimited, a wildlife conservation organization, is suing Bilgewater Boat Rental. Amphibians Unlimited contends that Bilgewater Boat Rental has abetted the spread of the parasitic worm Ribeiroia by failing to clean its boats before moving them from lake to lake. Bilgewater Boat is thus partly responsible for the epidemic of frog deformities, and should bear some of the costs of mitigation.

Note that the scientific merit of Amphibians Unlimited’s case depends on the validity of the hypothesis that Ribeiroia infection causes deformity in frogs. You are a scientist who has been hired by one of the litigants to put this hypothesis to the test. It will be useful to consider, as you work through the tutorial, how your interpretation of the evidence might be influenced by whether you have been hired by Amphibians Unlimited or by Bilgewater Boat.

Your task is to discover the cause, or causes, of extra-limb deformity in a particular population of frogs. Many of the frogs have the typical complement of four legs; others, however, have five.

The population is split across two ponds. You will first determine if there is a difference in the frequency of deformities between the two ponds. If there is a difference, you can take this a clue that will help you pinpoint the cause of deformity.

When there is a difference in the frequency of deformity in the two ponds, it could be due to parasitic worms, genetics, a combination of worms and genetics, or random chance. I know, because I wrote these causes into the different scenarios available in the simulation!

FrogPond is a work in progress, as is this tutorial. If you have comments or suggestions, please get in touch with me at herronjc at uw.edu. Thanks!