Lab 12: Animal Behavior

Pill bugs, roly-polies, potato bugs – what do you call ‘em?

(either way they’re crustaceans)

The Test Subjects

• For our animal behavior lab, we’ll be using the common pill bug (or whatever).– Official name: Woodlouse or Armadillidium vulgare

http://backyardsafari.files.wordpress.com/2010/11/0-pillbugwalking.jpg

The Test

• In this experiment, you’ll be running a test to determine behavioral preferences of the pillbugs.

• You’ll be using a container in which one side provides a certain stimulus and the other side provides a different one.– What exactly those stimuli are is up to you, but you

need to decide that now.– You ultimately need three different stimuli, and can

use combinations of others.

The Stimuli

• Some stimuli to consider:– Light/dark– Sweet/sour (acid/base)– Saltiness– Temperature

• (cold doesn’t work well for them so that’s obvious, but you can compare heat to ambient temperature)

– Spicy– Light color

• Make this decision via a written proposal in your lab notebooks and by writing it on a piece of paper (and turning it in).

• You always need a control, however – one side of your choice chamber is always going to be a plain ol’ damp cotton ball.

The Procedure

• Follow the procedure for Lab 12 in your lab manuals.– The lab manual uses fruit flies; we’ll be doing the

same experiment but with our pillbugs.• We’ll need to construct a choice chamber, which

for us is simply two bottles whose bottoms have been cut off and taped together.– Label each end A and B so you can keep track of stuff.– Be sure the bottles overlap a little so that, when

taped, you don’t have any exposed adhesive.

The Procedure

• Take your 20-30 pillbugs and place them into the chamber.

• Place two damp cotton balls (just water) on either side. Make sure your cotton ball is stuck inside the cap and doesn’t fall in.

• Let the test subjects mill around for a little bit.– Now’s a good time to make hypotheses for which of your

stimuli they’d prefer over others.• You’ll have to “extend” certain things.• For example, if you read that they live under logs and rocks, then

they’ll likely prefer darkness to light.• For example: If they eat mostly decaying wood (a carbohydrate),

they’ll probably also enjoy things that have sugar.

The Choices

• Of course, in order to reject the null hypothesis we need choices.

• Trade out one of your cotton balls for a “stimulus.”

• Write down how many pillbugs are on each side. Only do this once the entire experiment – you’ll see why later.

• Provide another 5 minutes for more pillbug millage.

The Choices

• After those five minutes, count the pillbugs on each side and record the information.

• Move to your next stimulus.– You’re ultimately going to do two trials for each

stimulus, but you’ll do it in the order of:• Stimulus 1 (Trial 1)• Stimulus 2 (Trial 1)• Stimulus 3 (Trial 1)• Stimulus 1 (Trial 2)• Stimulus 2 (Trial 2)• Et cetera…

Assorted Important Stuff

• For chi-squared purposes, ignore the original count of how many are on each side.– Your “expected” values are 50% are on one side and

50% are on the other.– The lab manual says to do otherwise – ignore that

too.• RUN MORE THAN ONE TRIAL AT ONCE!– If everyone has enough pillbugs for one run and

there are still some left over, get some more.– If not, just be efficient with your time.

Overall Sequence1. Create choice chamber.2. Put around 20 pillbugs in the choice chamber.3. Put a damp (with water) cotton ball in each side.4. Provide 5 minutes of “milling around” time.5. Record how many are on each side. This is your control.– Only do this step once.

6. Trade one cotton ball out for a dry one.7. Provide 5 minutes of “milling around” time.8. Count how many are on each side.9. Repeat steps 6-7 with a different stimulus.10. Repeat step 9 for all your stimuli to complete a second run for each.• While you’re waiting: Complete a chi-squared analysis for the control

data. Ensure that there’s no significant preference shown.• Is there a preference shown? Consider that for your lab write-up. It may

invalidate your results (but will not cost you points).

Formal Lab Report Details

• Refer to the file Lab Report Formatting Guidelines and Rubric found in the Labs section of my website.

• Besides what’s contained therein, here’s some other stuff to know:– It must be typed. Graphs need to be done in Excel or a

similar program.– You will work as a lab table to create a formal lab report.– You may divide the work any way you like, but I suggest

each taking a section and rotating duties for each lab.

Your lab report must include:• Chi-squared analysis for each stimulus• Chi-squared analysis for the class’s data (for dry cotton – more

later)• Table of results• Graph of results (best done as a summed paired bar graph for

each “stimulus” – Side A and Side B totals)• Discussion of your hypotheses – does your data support them

or not? Importantly, why?• Discussion of relevant questions as found on Page S150 and

S151 of your lab manual.• Discussion of limitations of your experiment or corrections that

could be made.– This part’s important and will not cost you any points.

• In fact, the more critical you are of your own work, the happier I’ll be.

Graphing Tips

• Here are three nice little graphing tips for the rest of your science lives:1. Dependent (measured) variables go on the Y-axis,

independent (controlled) variables go on the X-axis.2. Use bar graphs if there is no continuous relationship

among the different variables.3. A good, cheap, consistent graph title is “_____ as a

function of _____.”• For example, “Plant growth as a function of light level.”

Chi-Squared Details

• Since pillbugs either went to Side A or Side B, you only have one degree of freedom (df).– If you somehow counted “middle” separately, that would make for

3 degrees of freedom.• We have to assume that each side of the bottle is originally

equal, so your “expected” numbers on each side represent half of the total number of pill bugs.

• For each of your stimuli, your chi-squared test will use these variables:– Observed: [what you counted]– Expected: 10 (or whatever is half of your total)– Degrees of freedom: 1.

Chi-Squared Details

• You’ll also do a chi-squared analysis for your control data.• If you had, for example, 17 on one side and 3 on the

other prior to introducing any stimulus, you’ll test to see whether that’s a significant difference.

• To put it another way, suppose one of the two bottles is preferred for some other reason.– Tastier saliva residue, maybe?

• If our control numbers suggest that there is a significant difference in our bottles themselves, we need to view our other results differently.– Continued…

Chi-Squared Details

• For another example, suppose after your control run, 17 pillbugs were on Side A and 3 were on Side B.

• You trade out Side B’s cotton ball for something acidic.• After 5 minutes, Side A = 19 and Side B = 1.• A chi-squared analysis would say that’s significant compared

to the expected 10/10.• However, is that significant if we expected 17 and 3? Not

really.– So doing this test of our control data helps us ensure that the

control really is a control, and that each side of the bottle really is equal.

– Ideally, the control results would be insignificant, but if they’re significant, just be sure you address that in the lab report.

Final Note

• For the “wet/dry” runs, let’s pool our class data.

• Take a moment to sum your runs’ numbers for each category.

• I’ll sum the data and include it in the “Assignments” page listing for our lab report.– Maybe your wet/dry run is insignificant, but the

class’s data shows significance. We’ll see.