Gizmo Peppered Moth

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Use the Gizmos to complete the questions below.

EQ: How does environment impact natural selection process?

Scientific Background:

The story of the peppered moth, Biston betularia, is one of the best-known examples of natural selection in action. The peppered moth is common in Europe, North America, and Asia. It shelters on trees during the day and is eaten by birds. Peppered moths are found in three forms, or morphs:

 Biston betularia morpha typica is light gray in color and speckled.

 Biston betularia morpha carbonaria is dark gray in color.

 Biston betularia morpha insularia is intermediate in color. (This morph is not shown in the Natural Selection Gizmo.) Can you spot all the moths? Prior to 1800, the typica morph was much more common than the darker carbonaria morph in the English countryside. The speckled-gray moths blended in well with light-colored tree bark and lichens. The dark carbonaria form contrasted with the tree bark, making it easier to spot. During the 1800s, the Industrial Revolution changed the landscape of England. New coalpowered factories spewed tons of dirty smoke into the air, blanketing the forests with soot. The lichens on tree trunks died, and tree trunks were darkened. When this happened, the typica form was easier to spot than the carbonaria form, and as a result more were eaten. By 1895, dark moths accounted for nearly 100% of the total population in some forests. The pattern of darkening is described by the term industrial melanism. Throughout the 20th century, air quality improved, trees became lighter in color, and the proportion of typica moths increased. Today, carbonaria is almost as rare as it was before the Industrial Revolution. Historical connection: Peppered-moth controversy In the 1950's, Bernard Kettlewell conducted a series of experiments to test the hypothesis that natural selection, and more specifically bird predation, was the cause of industrial melanism in the peppered moth. Kettlewell released marked moths into polluted and unpolluted forests. In the polluted forests, dark moths were recaptured at a higher frequency, indicating that light moths were predated upon more by birds. The opposite was true in the unpolluted forests. In the past two decades, some controversy has erupted over the validity of Kettlewell's methods and conclusions. For example, Kettlewell released moths during the day, a time when they are normally at rest and less likely to select an ideal hiding place. Other scientists have claimed that the moths normally rest on the undersides of branches, rather than on the exposed trunks. If this is the case, their coloration may be less of a factor. Starting in 2000, lepidopterist Michael Majerus began an experiment that was designed to address many of the criticisms of Kettlewell’s results. Every night Majerus released both light and dark moths into his garden, which contained trees that were covered in lichen and therefore favorable to the light moths. The next morning, he noted the resting place of each moth, and then checked again four hours later to see which moths had survived the morning. As Majerus expected, dark moths were eaten at significantly higher frequencies than light moths.