Lab 3 Payton Rodgers

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Feb 20, 2024

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Popula’ons and Natural Selec’on The Peppered Moth ( Biston betularia ) has gene2cally controlled varia2on in their colora2on and can range from nearly all black to white with black spots. Informa2on and images above are from: h@p://cyberbridge.mcb.harvard.edu/evolu2on_2.html The main predators of the peppered moth are birds, which are highly visual predators. The moths are ac2ve at night and rest on trees during the day. Predators are more likely to see prey if they stand out from the background. Thus, moths that are well camouﬂaged against the tree will be more likely to survive to reproduc2on and pass on their genes to the next genera2on than individuals that stand out. Put another way, individuals that are camouﬂaged have higher reproduc’ve fitness and greater chance of contribu2ng their alleles to the future popula2on. If this natural selec’ve pressure is strong enough, the frequencies of the alleles controlling colora2on will change in the popula2on with each genera2on leading to change in the rela2ve abundance of the phenotypes in the popula2on. Like humans, the peppered moth is a diploid (2n) organism, meaning there are two copies of each gene locus. So, an individual in a popula2on can have a genotype of AA, Aa, or aa. The ‘A’ allele for dark-colored wings is dominant over the ‘a’ allele for light-colored wings. Moths with a genotype of AA or Aa will have a dark wing phenotype, while moths with a genotype of aa will have a light wing phenotype. In this example, 3 different genotypes (AA, Aa and aa) result in 2 different phenotypes: dark-colored and light-colored wings. A popula’on can have any number of individuals with different genotypes, and consequently with different phenotypes. The rela2ve abundance of dark-colored and light- colored moths in a popula’on will change as the result of the differen2al survival and repor2on of moths with different phenotypes that survive to pass on their alleles to the next genera2on. Each parent contributes one of their alleles for colora2on to each of their offspring. For a light- colored offspring to result, both parents have to contribute an ‘a’ allele to that individual.

1. Which moth is best camouﬂaged in this picture? (1 pt) ( h@ps://alexhyde.photoshelter.com/image/I0000DyMGnqGwJHk The dark peppered moth on the leY side in the photo is camouﬂaged be@er than the white moth. 2. Given the background in this image, moths of which colora’on will have higher reproduc’ve fitness? (1 pt) h@ps://alexhyde.photoshelter.com/image/I0000CBnr4dUjKb4 The moths with the light colora2on will have a higher reproduc2ve fitness because they blend in be@er and therefore have a be@er chance of surviving. Selec2ve pressures can change as environments change and individuals that had low reproduc2ve fitness in one environment may have higher fitness in another environment. Peppered moth popula2ons in England experienced a major change in their environment during the industrial revolu2on, which began in ~1835. Prior to the industrial revolu2on, trees were covered in light-colored lichens but as the industrial revolu2on progressed the lichens began to die off and expose dark-colored bark. Due to the change in background, light colored moths were selected against despite having higher fitness prior to the industrial revolu2on. Later in 1955, with decreased pollu2on, the lichens began to regrow. In this lab, we will simulate the phenotypic and genotypic changes in the moth popula2ons over 2me as changes in selec2ve pressures change which individuals have higher reproduc2ve fitness. You will play the role of the bird. Navigate to the simula’on here: h@ps://virtualbiologylab.org/NetWebHTML_FilesJan2016/IndustrialMelanismModel.html At the start, it is 1830 and the trees are covered in lichen because it is before industrializa2on. There are 20 moths on the “tree” in the right panel. To run the model, set your foraging 2me for 5 seconds and click “go.” A bird will appear in the “tree” panel, which you control as your computer cursor. Click on the moths to eat them. Eat as many as you can in the 5 seconds. When 5 seconds is up, the bird disappears. On the leY, you can see your “catch rate” which tells you how successful you were at catching moths. You can also read the phenotype and allele frequencies of the remaining moths – these moths will have the chance to pass on their genes to the next genera2on. Click “go” again and the model creates 20 new moths based on the genotypes of the poten2al parents and the years are advanced by 2. AYer clicking “go”, your bird appears, you forage, and repeat un2l you reach 2020. The lichens begin to die off in 1835 and start to grow back in 1955. You will need to record your data at various points in the simula2on using the table on the next page. You will then use your data to graph changes in genotype and phenotype frequencies in the moth popula2ons over 2me.

3. Fill in this data table as you advance your simula’on. (Required for making the plots.) A Phenotype Frequencies Allele Frequencies Year Dark Light Dark (A) Light (a) 1830 0.1 0.9 0.05 0.95 1840 0.063 0.938 0.05 0.95 1850 0.214 0.786 0.12 0.88 1860 0.083 0.917 0.05 0.95 1870 0.583 0.417 0.23 0.77 1880 0.154 0.846 0.18 0.82 1890 0 1 0.08 0.92 1900 0.167 0.833 0.13 0.88 1910 0.5 0.5 0.19 0.81 1920 0.95 0.05 0.7 0.3 1930 0.727 0.273 0.63 0.38 1940 0.667 0.333 0.45 0.55 1950 0.636 0.364 0.36 0.64 1960 0.917 0.083 0.64 0.36 1970 0.923 0.077 0.71 0.3 1980 0.071 0.929 0.29 0.71 1990 0.077 0.923 0.05 0.95 2000 0 1 0.05 0.95 2010 0 1 0.05 0.95 2020 0.071 0.929 0.05 0.95

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Copy and paste your data into Google Sheets, or another spreadsheet program. 4a. Plot the frequency of the dark phenotype over ’me. Paste your plot here. (5 pts) • Make a sca@er plot with connec2ng lines where years the x-axis and the frequency of the dark phenotype is the y-axis. • Adjust the y-axis so that it shows data from 0 to 1, no more and no less. • Add axis labels to the plot. X-axis should be “Calendar Year.” Y-axis should be “Frequency of Dark Phenotype.”

4b. What is the maximum frequency of the dark phenotype? In which year(s) does this occur? (1 pt) The maximum frequency of the dark phenotype is 0.95, occurring in 1920. 4c. Under what environmental condi’ons did the frequency of the dark phenotype increase? (1 pt) The dark phenotype increased during the Industrial Revolu2on, where smoke was prominent in the air. The trees in the areas began to show dark-colored bark because of the lichen on the trees dying. 4d. Under what environmental condi’ons did the frequency of the dark phenotype decrease? (1pt) The lichens men2oned in the previous answer began to grow back, and they are lighter in color so aided the light moths compared to the dark moths. 4e. Explain why the phenotype frequencies changed. (2 pts) The frequencies changed based on the environment at the 2me. For example, because the industrial revolu2on killed the lichen on trees and uncovered dark bark, more dark-colored moths were able to survive and reproduce compared to the lighter moths that were easier to find. When the lichen began to grow back, more light moths were surviving and reproducing compared to the dark moths. 5a. Plot the frequency of the dark allele (A) over ’me. Paste your plot here. (5 pts) • Format your plot like you did similar 4a, but this 2me the y-axis should be labeled “Frequency of the dark allele (A).” • (This plot should look similar to the plot in the app in the lower leY.)

5b. Explain why 100% of individuals in the popula’on could be the dark phenotype in one genera’on and light moths s’ll occur in the next genera’on. (3 pts) This is because of the genotype of the dark moths. The AA genotype creates dark moths, but so does the Aa genotype. If two Aa moths are to breed, their offspring has a chance of being a light moth. The chances of this happening are about 25%. The dominant allele is dark, and the recessive allele is white. AYer comple2ng the lab assignment, take the quiz on Canvas. The quiz will ask you to report some of your answers from this lab and will provide you with feedback. You should feel free to correct any answers on your laboratory assignment you found were wrong aYer taking the quiz before submirng this assignment to Canvas. You may retake the quiz twice and you will receive your highest quiz score

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