The peppered moth ( Biston betularia ) has a light-colored and a dark-colored fo

Question

The peppered moth (Biston betularia) has a light-colored and a dark-colored form. After clean air legislation was enacted in England in 1956, tree surfaces lightened over time because of the reduction in soot and the growth of lichens on the trees’ bark (lichens are light in color, and they grow poorly in polluted air). During this period, the light-colored moths increased in frequency.

Suppose that researchers performed an experiment in which they darkened the trunks of trees in an area where tree surfaces were light in color. Prior to this experiment, about 90% of the moths in that area were light in color. After darkening the tree trunks, researchers released 1,000 moths per year for each of the next 7 years. The proportions of light- and dark-colored moths that they released each year matched the proportions observed in the field. Each year, they determined the number of the released light- and dark-colored moths that were eaten. The results are shown in the table.

Question 1. Suggest a hypothesis that explains the initial high frequency (ca. 90%) of light-colored moths. Based on this hypothesis, predict how the frequency of light-colored moths should change over time in this experiment.

Question 2. Use the proportions of light-colored moths that were released each year to determine whether light-colored moths were increasing or decreasing in frequency in the area where the experiment was conducted.

Question 3. Calculate the percentages of released light- and dark-colored moths that were eaten each year. Do these results support the hypothesis that you developed in Question 1? Explain.

Year No. of light moths No. of light moths No. of dark moths No. of dark moths released eaten released eaten 904 226 96 18 2 860 240 140 23 808 178 192 35 4 763 164 237 47 740 199 260 4 688 178 312 50 7 653 182 347 52

Explanation / Answer

Answer 1) It can be hypothesized that initially white moths prevent eaten by birds because they make camouflage with surrounding. White colour surrounding with white moth birds fail to identify moth and these remain escaped. But with time colour of moth counteract which make easy visibility to birds and are eaten up. With time evolve white colured moth decreases and dark coloured moth increases. Means percentage of white moth that are eaten initially are more than dark moth which decreases with time.

Answer 2) Light coloured moth are decreasing with time because they get easily identifiable in dark back ground, while the percentage of dark moth increases.

Answer 3) 1st year - % of light moth eaten = 226/904×100 =25%

1st year % of dark moth eaten = 18/96×100=18.7%

For 2nd year % of light moth eaten = 240/860×100= 28%

For 2 nd year % of dark moth eaten =16%

Same for all year

For 7th year % of light moth eaten =182/653×100= 28%

For 7th yr year % of dark moth eaten 52/347×100=15%

Yes hypothesis hold true.

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