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 Natural Selection of the Galapagos Origami Bird (Avis papyrus) and the DNA Connection: Student Handout BACKGROUND The process of natural selection has been shown to be the primary way by which new species can evolve from previous species. There are three conditions on which evolution by natural selection is based: 1. Inheritable traits vary in a population (random trait variation); 2. Differences in fitness (ability to survive and reproduce) depends on the interaction of those traits in a population with the particular environment occupied by that population (differential survival); and... 3. Traits passed on and accumulate: The inheritable traits of the fitter individuals tend to accumulate and characterize the features of the new population. Figure 1: Visual illustration of the three conditions of evolution by natural selection Understanding these conditions can be tricky. Part of the difficulty stems from the fact that misconceptions acquired over time (from home, the media, teachers, books and movies) become deeply set and hard to repair. One of the most common misconceptions is about random mutations (unpredictable changes in the genes of individuals). Many people also fail to realize that there is a non-­‐random part of natural selection. It's the "selective" process, where certain gene combinations in a given environment enable some individuals to survive and produce more offspring than other gene combinations in the same environment. The word "selection" does sound like somebody is doing the selecting, and since people often make selections based on their needs or desires, we tend to think (incorrectly) that natural selection is a process for meeting a need. But it really does not work that way. That is a "Lamarckian" view of evolution, and many studies have consistently shown that the Lamarckian idea does not fit the observations. This lesson is intended to provide you with experiences to show how random mutation and natural selection for fitness actually do operate to change traits in living populations over multiple generations. INTRODUCTION to the Galapagos Origami Bird Study:
The Galapagos Origami Bird (Avis papyrus) was brought from South America and
introduced to the desert-like Galapagos Islands. It feeds on the sparse berries and
it drinks from limited natural springs. Only those birds that can successfully fly
between the distant islands will be able to live long enough to breed. In this lab,
you will breed several generations of these birds, where random mutations produce
random variation, from which the environment selects for long distance flying. Look
for changes in their population over several generations, measuring reproductive
success by the maximum distances they can fly.
We will be working with hand-made "straw birds" (Avis papyrus), all built basically
the same way (see page 5: Building Birds, with construction details and figure 2
showing the general appearance of the typical bird). Each generation of "birds" will
face the same selective pressure: greater survival for flying the greatest distance.
The individual in each generation that can fly the furthest (the "winner") will
survive and produce 3 offspring. Those offspring will have various mutations occur in
their DNA that may lead to new traits such as wider wings or longer bodies. The
two birds that did not fly furthest (the non-winners in each generation) will die.
(They can be used to build two of the three new birds of the winner's offspring).
MATERIALS:
4 straws (non-bending)
paper for cutting wing strips
scissors
clear tape
paper clips
Gametes Mutation Box (GMB)
Plastic sheet covering GMB
Dry-erase pen
Random Spinner #1
Random Spinner #2
2 Mutation Table
Results Sheet 1
Results Sheet 2
Masking tape
Tape measure
GETTING READY: Look at the top of Results Sheet #1, the DNA sequence for the original parent: (A G C T A). Now see the Gametes Mutation Box (GMB), a sequence of DNA with 5 empty boxes. 1) Using the dry-­‐erase pen, copy those 5 letters (A G C T A) from the top row of the DNA strand of the original parent (P) onto the plastic sheet covering the DNA of the GMB. Letters go in the 5 empty boxes of the GMB, in that order. Leave blank the lower row of matching bases. 2) Build your parent bird (P) using the dimensions in the top right of first Results Sheet (see Building Birds: page 5). For this generation, your group will do the following: 3) Build 3 offspring. (the F1 generation) from the P bird. To save time, and just for this F1 generation, let first new bird (-­‐1-­‐) be genetically identical to its parent (so you can fly that parent bird as if it was its identical baby bird). Each of the other two birds will get one mutation each. However, before we can build those other offspring, we need to find out the random mutation that each baby bird will have: a. Spin Random Spinner #1 with numbers 1-­‐5 on it. This randomly generated number will tell you which base in the DNA strand in the GMB will mutate. Then spin Random Spinner #2. This will tell you the new base (letter) that the randomly selected base will mutate to. b. Record with dry erase pen on the plastic overlay the letter for that new base (if it's different than it was before). c. Look at your Mutation Table to determine what effect (if any) that mutation will have on the phenotype of the offspring. d. On your Results Sheet (F1 second new bird (-­‐2-­‐), record the changes (genotype, and phenotype results). e. Repeat step a-­‐d for the third F1 bird (-­‐3-­‐). Record results on the Results Sheet. f. Build the new baby birds (as adults) just like the parent bird EXCEPT for the new phenotype determined by the random mutation. Due to limited time, you should ignore any color change phenotypes, from base #2). g. You should have 3 new birds, each with its own mutation and phenotype (with the parent bird standing in only for the first F1 bird) when you are done. 4) Fly the new generation (3 birds). The one that flies the furthest (or the furthest average of three flights, if time) will survive and reproduce, becoming the new parent bird: the "winner." (The bird with the original parent phenotype can be the one that wins and produces in the next generation, but it might not). See Flying details below. 5) Repeat steps 3-­‐4 until you have completed both Results Sheets through four generations (f4) of offspring. Instead of using the "Parent (P)" bird each time, use the "winning" bird -­‐ the one that flew the longest (average) distance in the previous generation as the new parent bird. 3 FLYING THE BIRDS a. Take your 3 birds to the assigned place (hallway, empty room, etc.). Be sure to take a tape measure to measure the distances flown. If possible, use metric tape measure. If not available, measure in inches and translate to cm. Just multiply your inches measurement (estimated to nearest tenth of an inch) by 2.54 Record the results. b. Standing at the "take-­‐off" line (strip of masking tape), release each bird with a gentle, overhand pitch. Try to release all the birds in the same way. c. For each flight, have a team member place a small piece of tape where the "head" (paper clip end) landed. Number the tape of each landing with the bird number (and its flight number: 1st, 2nd, 3rd if you are averaging multiple flights). d. Have two team members using tape measure (or meter stick) to measure distance flown for each bird from the take-­‐off line to its landing spot. e. If time allows, fly each bird 2 or 3 times, record distances, and find the average distance flown. Your teacher will tell you whether to just do 1 flight each, or find averages. f. Circle the bird on your Results Sheet that flew the longest distance (or longest average distance). That bird will be the parent of the next generation. g. Return to your classroom, and using dry-­‐erase pen, put the proper genetic sequence for that new parent on the transparent plastic in the Gametes Mutation Box. h. Using the 2 Random spinners, figure out the mutations for all 3 birds for the next generation (including the winner "parent" bird). See item 3) a-­‐g, page 3. Fill in that information on your Results Sheet for the appropriate generation. f. Repeat the Flying instructions (a-­‐h). Continue to breed, test, and record data for as many generations as you can in the time we have, at least 4 generations if possible. DISCUSSION Answer the Discussion Questions (attached, page 6) on a separate sheet of paper. These may be collected. 4 BUILDING THE BIRDS
MATERIALS FOR BIRD BUILDING:
4 non-bending straws. If possible, use big plastic straws about 7 mm diameter x about 21 cm
long. These are easier to tape the paper-loop wings onto (rather than the little 4 mm
straws), and they're more durable. (An interesting variable for a special project later
might be to compare flight distances built of 7 mm straws with those built of 4 mm
straws.)
6 Strips of paper. Measure and cut the first two wing-strips for the ancestral (parent) bird: 2 cm
by 20 cm. Be prepared to cut more wing-strips as determined by mutations. Use 20 pound
copy-paper. (An interesting variable for a special project later might be to compare birds
with copy-paper wings to birds flying with heavier paper wings, e.g., construction paper,
or even manila folder paper).
Clear tape for connecting ends of paper strips with 1 cm overlap), and for attaching those wingloops to the straws.
Metric ruler for measuring.
Scissors for cutting paper strips.
Small paper clips for head-end of bird
ASSEMBLING THE ANCESTRAL BIRD (the P generation):
a. Cut two strips of paper, each 2 cm x 20 cm.
b. Loop one strip of paper with a 1 cm overlap and tape together.
c. Repeat for the other strip.
d. Tape the overlapped part of each loop 3 cm from the end of the straw (see figure 2, below)
e. Place a paper clip in the straw at the head end of your bird. Mark that end "head."
Figure 2 Basic construction of an Origami Bird. You will need to insert a paper clip in one
end of the straw. Label that end with ink: "head."
5 DISCUSSION QUESTIONS
On a separate sheet, write your name and names of your teammates at the top. Then title the page
"Discussion Questions". Using the numbers and letters shown with these discussion questions
below, answer each question as briefly but clearly as you can. Your answers may be collected at
the beginning of the next class period, or they may first be discussed with your team, then shared
with all the other teams in a class-wide discussion, depending on what your teacher announces.
1. Did your study produce more birds flying longer distances than the original bird? For the final
winner bird, for each wing, measure its distance from head, width, diameter of the loop:
a. Front wing
b. hind wing
c. Number of paper clips in head?
2. Evolution is usually the result of two processes: variation and selection.
a. How was variation produced among the offspring?
b. How did the environment select for the offspring to breed in the next generation?
3. Compare your youngest bird with your neighboring teams' youngest birds (the winners in their
last generation):
a. Compare and contrast the wings of the other birds with your own (sizes, positions).
b. Explain why some aspects of the birds are similar.
c Explain why some aspects of the birds are different.
4. Predict the appearance of your youngest bird’s descendants if:
a. the selection conditions remain the same and the longest flying bird survives to
produce the most offspring.
b. the selection conditions change (the shortest distance flying bird survives to produce
the most offspring.
c. the selection conditions change and the bird whose color blends with its environment
survives to produce the most offspring.
5. Explain the mechanism of microevolution in the origami bird using the six terms: DNA,
mutation, variation of traits, survival rate, natural selection, and random.
6. Our bird evolved by natural selection, not by Lamarckism. How can you explain this?
7. Did your understanding of “evolution,” “natural selection,” "random," and/or “mutation”
change after the study? If so, which term(s), and how did your understanding(s) change?
8. Write your overall impressions of the study.
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