An Exploration of Animal Behavior In Isopods

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1 An Exploration of Animal Behavior In Isopods James Watson with Francis Crick AP Biology Point Pleasant Beach High School November 3,4, Abstract Isopods, (also called pill/sow/potato bugs) are terrestrial crustaceans that consume decomposed leaves or other plants. In these experiments, the isopods were presented with choices of three different environmental variables, presented as a resource gradient. Their behavior was observed and recorded, specifically the climate that they preferred, over the course of 10-minute experiments performed in choice chambers. Various climate situations such as Light vs. Dark, Hot vs. Cold, and Wet vs. Dry were tested and observed. The results showed that, as expected, the isopods favored dark, cool, wet environments over dry, lighted, warm ones. Introduction Ethology is the study of animal behavior. This involves observing an organism s behaviors, and interpreting what is observed. In a hybrid of psychology and ecology, ethologists study and observe an organism s reactions to each other and to the environment around them and try to attribute a cause or motivation to such behavior. Behavior in animals may be learned or genetic (innate). An animal can display many different types of behaviors, two examples being taxis and kinesis. Taxis behaviors are deliberate movements toward or away from a stimulus. Kinesis is a random movement that is not oriented toward or away from a stimulus. Taxis behaviors are generally driven by the physiological needs of an organism. Other behaviors were observed in the isopods in these experiments, such as agonistic - aggressive or submissive actions toward another organism - or mating behaviors. Both biotic and abiotic factors influence the behavior of organisms, which is largely rooted in selfpreservation. Favorable conditions are desired by an organism to maximize its own survival. Because of this, an animal must search for the environment to fit its structure and lifestyle. This is called habitat selection. In this series of experiments, several abiotic factors were manipulated in order to test several hypotheses regarding the survival behavior of groups of isopods. To observe animal behavior in this series of experiments, isopods were isolated in a controlled environment and were observed to investigate their responses to environmental variables. Isopods are crustaceans with a hard exoskeleton, eyes, seven pairs of legs, and antenna (Figure 1), which they use, to various effect, to interpret their environment. They can be seen to tap the surface of objects with their legs and antennae as they negotiate their way around. In the three choice gradients set up in these experiments, it was hypothesized that isopods would prefer the wet side to the dry side of the choice chamber, the cool side over the warm side, and the dark side over the light side because they are used to living in cool, dark, moist conditions, such as under rocks or in rotting logs. These conditions are the most conducive for their survival, given that their gills function best 1

2 when moist. Dark and cool conditions should limit evaporation of moisture and make breathing easier, and thus enhance chances of survival. Materials and Methods For each experiment, a choice chamber was utilized. It consisted of a two plastic petri dishes, attached side by side. A small doorway was opened across the center to allow access between the two dishes. The first choice presented was that of a wet versus a dry environment. A piece of plain white paper was placed in the bottom of the chamber and was moistened with tap water on only one side of the choice chamber. Five isopods were placed on each side of the chamber (total of 10) to begin the experiment. The number of animals on each side of the chamber was then observed and counted every 30 seconds for ten minutes. This was recorded in a laboratory notebook. Three trials were carried out, using different groups of isopods, and the results were averaged in Table 1 and displayed in Graph 1. For the next experiment, the same choice chamber setup was cleaned and utilized again, this time to examine how the isopods would react to differences in a light versus a dark environment. A clean, dry piece of white paper was placed on the floor of each side of the choice chamber, and five isopods were placed on each (total of 10) to begin the experiment. One half of the chamber was then covered with an opaque cloth, to create a dark environment on one side. The number of animals on each side of the chamber was then observed and counted every 30 seconds for ten minutes. This was recorded in a laboratory notebook. Three trials were carried out, using different groups of isopods, and the results were averaged in Table 2 and displayed in Graph 2. For the final experiment, the same choice chamber setup was cleaned and utilized yet again, this time to examine how the same isopods would react to a cool environment. A clean, dry piece of white paper was placed on the floor of each side of the chamber, and five isopods were placed on each side (total of 10) to begin the experiment. One half of the chamber was covered with an plastic ziplock bag that had been filled with cold tap water and ice (10 o C), to create a cold environment, while the other side was left at room temperature (22 o C). The number of animals on each side of the chamber was then observed and counted every 30 seconds for ten minutes. This was recorded in a laboratory notebook. Three trials were carried out, using different groups of isopods, and the results were averaged in Table 3 and displayed in Graph 3. Data and Observations Figure 1 Isopod Anatomy 2

3 Table 1: Isopod Distribution: Wet vs-dry Environments (average of three trials) Time (mins) # wet chamber # dry chamber Graph 1 Isopod Distribution, Wet vs-dry Chamber (average) Isopod Distribution number of isopods Time (minutes) # dry chamber # wet chamber 3

4 HINT: Include the rest of your data on the next few pages!!! Note- Make sure tables and associated graphs appear together, in the same sequence they are mentioned in M&M section. Make sure tables and graphs are numbered sequentially and include a descriptive title Make sure your tables and graphs are all consistent in their size. No Calculations section in necessary for this particular lab, however a picture of the isopods and/or choice chamber might be useful. If you include a picture, label it as Figure 1, Figure 2 etc and give it a descriptive title. Note that when referring to Tables, Figures, etc in the written section of the report, they should be BOLDFACED. Some suggestions for your discussion (data analysis) section: 1. First, describe your findings! Use your graphs, tables, figures, etc to make your points! If you included ANY data in your lab report, it MUST be mentioned in the discussion section. 2. Do not simply recap the numbers in your data table, rather describe any trends your data shows. Estimate how long it took the pillbugs to acclimate to the chamber. Did the pillbugs exhibit kinesis, taxis? Both, at various times? How long until their behavior appeared to change from kinesis to taxis? How many minutes elapsed before a majority settled on one environment (if they ever did)? By the end of the experimental interval, how did they settle out? Had they settled on one? Or were they still choosing? 2. Did they show an overall obvious preference to one environment over the other? Can you support this? Discuss! Was it a slight majority? A vast majority?to what do you attribute this behavior? What advantage might this behavior have for the isopod? 4. Note any obvious errors in the experiment. How could the experiment be improved? How did your results compare to other lab groups? If you were to do this again, what would you change, if anything? Does this investigation warrant any further research? Does it bring up additional questions that might be investigated? example: Discussion When initially placed in the choice chambers, the isopods were observed to be moving around mostly randomly, by kinesis. After a minute or so, they began assessing their environments mostly through taxis. By touching surfaces with their antennae, and using their eyes, these animals were observed to be moving toward or away from stimulus. It is likely that they operate strictly out of innate self-preservation. Several of the outcomes of the three experiments performed agreed with the initial hypotheses proposed, based on where they are normally found in their natural habitat. In seeking out isopods, one might turn over logs, rocks, etc. These animals seem to be found in great numbers in such cool, dark moist places, so it was hypothesized that these conditions, when applied in a laboratory setting, would be preferred by the isopods. 4

5 As seen in Table 1 and Graph 1, at the end of the ten-minute experimental period, all of the animals had indeed gathered in the moist side of the choice chamber. As these animals are terrestrial crustaceans, they have breathing apparatus that are similar to those of aquatic crustaceans (crabs, etc). Physiologically, it makes sense that such gill-like apparatus would need moisture for gas exchange. Table 2 and Graph 2, clearly show a gathering of isopods in the dark side of the chamber, which agrees with the hypothesis that these animals prefer dark environments, perhaps to avoid predators or drying out. Table 3 and Graph 3, indicate that the isopods initially had a mixed preference for hot or cold temperatures, however at the end of the ten-minute experimental period, a slight majority had gathered in the cold side. This agrees somewhat with the hypothesis that isopods would prefer cooler habitats, perhaps to avoid drying out and to make breathing easier. In addition, when comparing results with other laboratory groups that performed similar experiments, it was found that most were in agreement regarding the isopod responses to these three stimuli. This would seem to further strengthen the reliability of the outcomes. Literature Cited Advanced Placement Biology Laboratory Manual for Students, Exercise 11, revised 2001 by the College Entrance Examination Board, pg Campbell, N, & Reece, J (2005). Biology 7th edition, AP. San Francisco, CA: Pearson, Education Inc. pages Isopod, Pillbug, Sow Bug Information. Center for Insect Science Education Outreach. The University of Arizona. Accessed September 17, < HINTS: For lab reports, at MINIMUM you should cite the lab manual, the textbook (specific pages!), and AT LEAST one web resource. How to Cite a Webpage in MLA format: Include the name of the website, the name of the editor (if given), the date of electronic publication (if given), the sponsoring institution (if given), the date of access, and the URL. Format: To cite a general website: o Name of website. Editor(s) of website. Date of electronic publication. Associated institution. Date of access <URL>. To cite a specific article from a website: o Author(s) of internet article. "Name of internet article." Name of website. Editor(s) of website. Date of electronic publication. Associated institution. Date of access <URL>. 5

6 Examples: A general website example: o BBC on the Internet British Broadcasting Company. 12 Apr < An example of a website with an article: o Smith, Fred. "New Football Recruits." Northwestern Football. Ed. Alex Shokey Northwestern University. 6 Jun < 6