Peppered Moth (Biston betularia) Lab
Standards Covered:
~Students know how natural selection determines the differential survival of groups of organisms.
~Students know variation within a species increases the likelihood that at least some members of a species will survive under changed environmental conditions.
Introduction:
At the time of its naming, the peppered moth was predominantly a light-colored moth with gray spots. It was common in England in the 1800s. Occasionally, people would find dark gray peppered moths, but those where less common. The peppered moth lives its life in the woods trying not to be eaten by the birds. Around 1850, people noticed that the darker moths began to be more common, usually in areas near coal burning factories. Burning coal produces lots of sooty black smoke. Our job today is to run a simulation to discover why there was an increase in the frequency of the dark colored moths in England in the mid-1800s.
Simulation Materials:
White background paper = trees with white bark
Newsprint background paper = trees with darkly colored bark
Small white squares = lightly colored (white) peppered moths
Small gray (newspaper print) squares = dark gray peppered moths
Simulation Roles:
Bird – One group member’s fingers will simulate the birds’ beaks. Birds must squint so that their vision is not 100%.
Timer – Times feeding period (5 sec).
Recorder – Records numbers of surviving moths (how many white squares are left and how many newsprint squares are left.)
Reproducer – For each square left at the end of the feeding period add another matching square to the background (example: if 3 white squares are left, then the reproducer adds 3 more white squares).
Everyone – Copy the chart below on your paper and make sure to include 5 rows for 5 generations.
Table 1: Population of peppered moths in England in the 1800s
Generation
/ # of light moths at start of generation / # of dark moths at start of generation / # of uneaten light moths (survivors) / # of uneaten dark moths (survivors)1
2
3
4
5
Simulation Instructions:
England in the early 1800s
1. Lay out the white background to represent the white tree bark found in the early 1800s in England.
2. Reproducer sprinkles 15 white squares and 15 newsprint squares randomly in a thin layer (DON’T LOOK, BIRDS!).
3. Timer says when to start and times bird feeding for 5 seconds. Bird must only pick up one moth at a time during feeding period and remember to squint so your vision is not perfect. Each feeding period of 5 seconds represents one generation.
4. At the end of this feeding period the Recorder records the number and colors of remaining moths in the background (the survivors).
5. Reproducer doubles the survivors of each color. Recorder now records this number as the beginning of generation 2.
6. Repeat this process through five generations or until only one color remains in the surviving population. Everyone – help monitor progress and don’t forget to record data!
Coal Burning Factories are Built Nearby: 1850s
7. Now you will change the background to the newsprint to represent the soot-stained bark of 1850s in England.
8. Everyone draw a table similar to Table 1 and title it, “Table 2: Population of Peppered Moths in England in the 1850s.”
9. Reproducer sprinkles 15 white squares and 15 newsprint squares randomly in a thin layer (DON’T LOOK, BIRD!)
10. Repeat steps 3-6 above. Don’t forget to record!
Graphing Data:
Create a line graph of your data. The x-axis will represent generations and the y-axis represents the number of moths present at the beginning of each generation. Use two colors to represent the two tree backgrounds and two symbols to represent the two different colored moths. You will have four lines: white tree/white moth, white tree/dark gray moth, gray tree/white moth, gray tree/dark gray moth.
Discussion Questions:
1. Describe the population of peppered moths in England in the early 1800s. What percentage of the total population were white moths and what percentage were dark gray moths?
2. Why did the number of dark moths gradually increase in the 1850s?
3. What might have happened to the peppered moth population in the 1850’s if they did not have color variation in their population –if there were ONLY white moths?
4. What changed first, the environment or the incidence of dark moths in the peppered moth population?
5. Assume that moth color is determined by two alleles. If gray is the dominant phenotype then what are the two possible genotypes for gray color (use P and p)?
6. If the white phenotype is recessive then what is the genotype?
7. Even though white is recessive why was this color more common in the peppered moth population of the 1800s?
8. Most coal burning factories today “scrub” the smoke (catch the particles of black soot) before it leaves the smoke stack. This makes it less harmful to the environment. What do you predict has happened to the moth population since factories began doing this?
9. Why does color variation create a survival advantage for the peppered moth species?