“THE ECOLOGICAL THEATER AND THE EVOLUTIONARY PLAY”
OBJECTIVES: Predict how ecology and evolution interact with each other.
STANDARDS: Biology Standards- SB5b, d; SB4 a, c, f; SCSh1-9
INTRODUCTION: Charles Darwin’s theory of evolution is based upon specific observations that he made and inferences
that he drew from those observations. Write down those observations and inferences.
Caenorhabditis elegans is an important model organism for geneticists and developmental biologists. Like fruit flies,
many strains have been described and cultured. In this activity, we will be working with wild type C. elegans and dumpy
(dpy) mutants of C. elegans. Conduct background research on wild type C. elegans, the dpy gene in C. elegans, life cycle
of C. elegans and competitive exclusion. C. elegans can be easily grown on agar on which a safe strain of E. coli has been
cultured. The worms use the E. coli as a food source.
In this activity, you will be trying to determine if one strain of C. elegans has an advantage over the other when grown in
culture.
MATERIALS:
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Wild type C. elegans(KSU, Martin Hudson)
dpy C. elegans (KSU, Martin Hudson)
Nutrient agar
OP-50 strain E.coli
Petri dishes
Pipettes
Worm pick
Video microscope
Digital cameras or cell phone cameras
Ruler
NIH ImageJ computer program (free download)
Depression slides
GENERAL TIMING: about 3 class periods
PROCEDURES: Obtain a petri dish containing adult wild type C. elegans and a Petri dish with the dpy mutant. Observe
the worms in each petri dish for 10 minutes each. Prepare a chart in which you note similarities and differences
(morphological and behavioral) between the two strains of C. elegans.
You will be placing equal numbers of the two strains of worms together in culture and allowing them to live together for
five generations. Based upon your observations of the two strains, state your hypothesis for what will happen when the
two strains live together.
Transfer 10 adult worms of each strain to a separate depression slide (10 worms/slide; 1 slide for each strain). Use the
video microscope at 100x magnification to display your worms. (If you have a dissecting microscope that is hooked upto
a camera you can use that as well) Take a photograph of each of your worm slides. Make sure you can see the anterior
and posterior ends of the worm before you take the picture. Use the NIH Image J to measure the length of each of the
worms in your photos. Your instructor will show you how to use this program. Record the lengths and calculate the
average length for each worm strain.
You will note that the agar surface of both cultures is covered with eggs. Using a spatula, transfer 50 eggs of each strain
to a new petri dish containing agar and E. coli. Over the next few days, you will allow the eggs to hatch and the worms
to grow to the adult stage. These adults will then also lay eggs. Obtain 20 adults to be used for measuring lengths as
outlined above. Transfer 50 eggs to a new petri dish. Allow those eggs to hatch and grow to maturity. Measure worm
lengths and transfer eggs as before. Repeat this procedure for a total of 5 generations.
RESULTS:
Gen 1 WT
Gen 1 DPY
Gen 2
Gen 3
Gen 4
Gen 5
DATA ANALYSIS: Use a t-test to determine if there is a significant difference in length between the two strains of
worms. Use Analysis of Variance (ANOVA) to see if there is a significant difference between the average lengths of the
worms for each of the five generations. Use the ANOVA calculator at www.physics.csbsju.edu/stats/
DISCUSSION: Was there a significant difference in the average length of the two strains of worms? Was there a
significant difference in the worm lengths over the five generations? If so, what caused the difference? Define
evolution. Did evolution occur over the course of the experiment?