Periwinkle Behavior

First review your knowledge of the steps in the scientific method:

1. Observe and read.

2. Ask questions.

3. Create a hypothesis.

4. Form predictions based on that hypothesis.

5. Design a test of your hypothesis using those predictions. Be aware of

variables- test only ONE at a time.

controls

significant amount of data

practicality

quantifiability (How will you measure things like “more”?)

6. Analyze the data generated by your experiment.

7. Accept or reject your hypothesis.

8. If rejected; review your hypothesis and your test and try something else.

9. If accepted; ask more questions.

Today we are going to use this process to explore the behaviors of periwinkles. Normally you would do library research, but I’ve done that for you and provided some information about periwinkles. You have observed or will be observing periwinkles in the field. But not today.

The eroded periwinkle, Littorina planaxis, lives in the very high splash zone intertidal areas of California rocky shores. They can be distinguished from the slightly lower dwelling L. scutulata by a white band curving inward in the base of the opening. They are highly tolerant of desiccation, temperature variation, and fresh water. They eat the microscopic film or cyanobacteria, diatoms and green algae. They don’t eat seaweed (macro algae). They can survive for weeks without food. Littorina are dioecious (separate sexes) but the sexes are indistinguishable-even to other periwinkles- until copulation is attempted by the males. Males are often found clinging to the shells of females.

Now that we know a little bit about periwinkles we are going to study how they maintain their position in the intertidal. They are very small and have very simple brains. They cannot see the whole area and decide to go so far up and no more. Yet they don’t end up wandering around the parking lot headed for the mountain passes nor do they get down to water lever.

Organisms often use taxis and kinesis to control their whereabouts. A taxis is a directional movement in response to a stimulus. A positive taxis causes the organism to move toward the stimulus and a negative taxis away. Some examples of taxes are:

photo taxis : light

geotaxis : gravity

rheotaxis : current flow

chemotaxis: chemicals (taste/smell) including ones produced by other organisms.

During kinesis an organism slows or quickens movement in response to particular stimuli. Why would that cause directional progress even if the directions of the movements were all entirely random? (A random walk) Like a taxis a kinesis can be in response to a variety of stimuli such as light or chemicals. When you think you have the answer to that call me over and tell me.

We will study how periwinkles use taxis/ kinesis to maintain their position in the intertidal. First create a hypothesis regarding periwinkle use of any of the taxes or kinesis. Remember you are trying to understand how periwinkles use taxis or kinesis to maintain their position is the intertidal, not why that position is advantageous and has been selected for. Then make your predictions and design an experiment to test your hypothesis. What outcomes would support your hypothesis? What would falsify it?

Briefly write this up and present your hypothesis and protocol to me for approval and advice. Do not start experimenting or do anything to the snails until I have Ok’ed your protocol.

Now perform your experiment/s. Record your data. What are your conclusions? Is your hypothesis supported? Speculate what you might change if you were going to repeat the work or change your hypothesis. Write this up and show me so we can discuss it.

A Scientific paper typically has the following parts:

1. Title and authors- that’s you.

2. Introduction- here you give background about the problem and your hypothesis or hypotheses.

3. Materials & Methods- Here you relate your protocol in such detail that someone else could exactly duplicate your work. Think of a cookbook.

4. Results- Here you give your data and observations.

5. Discussion- Here you tell the reader weather you believe your hypothesis is supported. (Not “proved true”.) Also discuss problems, suggestions for improvement and new ideas.

6. Conclusion- Give the reader the bottom line. What do we now know? Be brief.

7. Literature cited- Bibliography (we won’t have this section in our class reports because your texts and me are your only sources.)

Organize today’s work into a scientific paper. You will turn it in at the end of class. Neat hand printing is fine. If you use a word processor make sure you can get me a hard copy before class ends.

If time allows continue with your research, exploring the ideas you presented in your discussion. Always record your work. You can add it to your paper as an addendum.