Types of Natural Selection on Polygenic TraitsName ______

Working with your group, you will explore the types of natural selection. You are the predator who is eating organisms that show a range of colors. You will select the organisms according to the behaviors of the predator as indicated with each set of organisms. Your selection behaviors will show one of the following patterns of selection:

In stabilizing selection, the average form has the highest fitness. It results in very similar morphology between most members of the species.

In directional selection, a more extreme form of the trait than average shows the greatest fitness.

In disruptive selection, individuals with either extreme of the trait show greater fitness than the average.

  1. Open the container. Arrange the organisms by color on the large graph paper. Be sure that your graph is a normal distribution (which means you will make a bell shaped curve, with each color in a separate column).
  1. You will each obtain a graph paper that has been divided into sections from your teacher. The top left section will be used to graph the “before selection” distribution of organisms (it will be the same for all trials), and below you will graph the “after selection” distribution for each of the three examples. Graph the arrangement of the organism’s distribution on the smaller graph paper as a bar graph using colored pencils to indicate the colors of the organisms.
  1. Draw one set of instructions out of the envelope to determine which organisms to remove.
  1. Draw the “after” distribution of organisms in one of the spaces in the bottom row, being sure that you have the same colors in the same columns on both graphs so that you can compare them directly. If you have “0” of any organism left, leave the space on the graph at zero for that color. Do not remove the color from the graph!
  1. Return the organisms to the normal distribution.
  1. Draw the next set of instructions to determine what the shape of the resulting graph of the distribution will be after the next round of selection. Draw the graph as previously noted.
  1. Repeat step 4 for the third set of instructions in the envelope.
  1. Clean up by returning the organisms to the container, putting the instructions back in the envelope, and returning the setup to your teacher.
  1. Determine which type of selection each graph represents, and label each graph.
  1. Answer the questions, and hand in the graphs and questions. Be sure your graph axes are labeled correctly and you have a title on your graph before you hand it in.

Name ______

  1. What type of natural selection did you find for each of the simulations?

A =

B =

C =

  1. You have a population of flies with various wing lengths. The longer winged flies live at the top of the trees, the medium length live in the foliage, and the shorter lengths live on the trunks of the trees. During a wind storm, the flies with long wings are blown out to sea and drown. Which type of natural selection is this?

Why do you think so?

If high winds continue, will evolution occur?

Explain.

  1. If the same population of flies (before the wind storm) has birds eating the flies that they can see at the top of trees, and geckos eating the flies on the trunks of the trees, what kind of natural selection is the population experiencing?

Which wing length population is the most fit in this situation?

  1. If a species of fish has a predator that is unable to find the small fish, but unable to swallow the largest fish, what kind of natural selection is working on the fish population?

Explain what will eventually happen to the population.

Fig 1: Skittles population before selectionFig 2: Skittles population after selection with scenario 1

Fig 3: Skittles population after selection with scenario 2Fig 4: Skittles population after selection with scenario 3

  1. You are a neurotic newt with a couple of eating fetishes. You like to eat the food that is the easiest to find first. In this case, it means that you start with the type of organism you have the most of. You get carried away, and will not eat any other type until you have eaten all the organisms of that color. You then repeat the process by eating the next organism that you have the most of. Unfortunately, you are full after eating 20 organisms and stop eating.
  1. You are a frog that likes a challenge. You hunt the organisms that hardest to find. You start eating the organism you have the least of, and when that is gone, go on to the one with the next last amount. Unfortunately, you are full after eating 20 organisms and stop eating.
  1. You are a lazy lizard with a long tongue. You are attracted by the lightest color of organism. You move to where you can eat them easily, and eat them all. When these are gone, you do not want to move, so you eat only the organisms that were right next to them. When those are gone you may eat only the organisms that were next to them. Unfortunately, you are full after eating 20 organisms and stop eating.