Camouflage: A Model of Natural Selection

Introduction

Natural selection operates on the principle of survival of the fittest. Fitness can be defined as the suitability of an organism to a given environment. One might ask if one set of features favourable in one environment might prove unfavourable in another environment. In this lab you will test the following hypothesis: If survival is related to specific characteristics in a given environment, then altering the environment will decrease the survival rate. Once you have formed a conclusion to this hypothesis and how it relates to the adaptation of camouflage, you will apply this information to the peppered moths of Manchester, England. You will predict the direction of an adaptive shift and the resulting gene frequencies.

In this experimental model, the features studied will be the adaptation of camouflage in two very different environments. You will act as the predator and your prey will be two types of paper circles, one with a plain colour and the other with a printed pattern. Their environment will be either a sheet of plain coloured paper (butcher paper) or a sheet of paper with a printed pattern (newspaper want ads).

Materials and Equipment: per team of two students:

1 page of newspaper want ads

1 sheet of butcher paper of the same size

Envelope with 100 each of butcher paper circles and want ads circles cut with a paper punch

Suitable timer

Procedure

Work with a partner. One of you must always be the predator while the other will supervise the experiment so as to not introduce an uncontrolled variable. The experimenter’s job is to spread out the prey (paper circles) randomly for each trial making sure they are not piled up and that they thoroughly cover the sheet of paper. Also the experimenter will time each trial and record the data.

The predator’s rile here is to locate (count them, do not pick them up) as many prey of a particular colour as possible in 10 second trials. With the predator standing with his/her back to the hunting area, the experimenter will give a signal, the predator then quickly turns around and begins to spot and count the plain circles until the experimenter tells him to stop (at 10 seconds). The predator calls out his total. On the next trial, the predator attempts to spot and count just the printed circles for 10 seconds. These trials are each repeated two more times and then the environmental background will be changed to a printed pattern. Again three trials will be made attempting to spot and count each type of circle in 10 seconds this time starting with the printed circles first.

Important Notes:

1.  The particular predator, in this problem, only hunts for prey just before sunrise and just after sunset, therefore, the light in the room will be very subdued.

2.  After each trial the experimenter should rearrange all paper circles on the paper to make sure the population is randomly distributed. When all data is recorded compute your average and report the results to your teacher.

3.  Before you begin make a prediction.

Plain background / Printed Background
Trial# / # plain circles / # printed circles / # plain circles / # printed circles
1
2
3
Team
Average
Class
Average
%
died
%
survived
%
advantage

Prediction:

State in the hypothesis format (If…….. then …….)

Which circle on which background will get the lowest count? Why? (2 marks)

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Observations: (3 marks)

% advantage = % survived in population with most survivors

% survived in population with less survivors

Only fill in the % advantage in the space for the population with the most survivors.

What other observations did you make as a predator? (2marks)

What other observations did you make as an observer?

Questions:

1.  Darwin observed that there was great variability within a species. How did we illustrate this observation in our activity? (1 mark) ______

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2.  In natural selection, selective pressure is the factor that reduces the frequency of a particular phenotype more than another phenotype. In this model the phenotypes are plain and printed. What was the selective pressure on this population?(1 mark) ______

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3.  Some circles went uncounted and thus escaped predation. Why do some escape? (1 mark)

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4.  Is survival equal for each phenotype? Explain why or why not. (2 marks) ______

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5.  Darwin believed that the characteristics that contribute to superior survival will increase in frequency. If this experiment were to go on for generations, which phenotype do you think will become dominant? Why?

(1 mark) ______

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Discussion: (4 marks)

What was your prediction and was it correct?

How is this related to the peppered moth in England?

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