pillbugs and their preferred habitat conditions

pillbugs and their preferred habitat conditions Introduction To sufficiently grasp and understand the experiment on animal behavior, it is crucial to be knowledgeable of the organisms being observed, as well as the various types of animal behaviors present in nature. In this experiment the observed organism was the pillbug. Pillbugs, are also known as sowbugs or woodlice. They are classified as terrestrial isopods as they belong to the phylum Arthropoda, subphylum Crustacea, class Malacostraca, and order Isopoda. Morphologically they consist of three body parts which include the head, thorax, and abdomen. They have one prominent pair of antennae and one inconspicuous pair, simple eyes and seven pairs of legs. The thorax consists of seven separate segments and there are paired appendages, called uropods, that are located at the end of the pillbugs abdomen. The color of the pillbugs can vary from dark gray to white and they could have a pattern or not have one. With female pillbugs, leaf-like growths appear on the underside of the bugs at the ba se of some of the legs. These pouches are where the developing eggs and embryos are held. On the male pillbug, the copulatory organs are the result of modification in the form of elongation of the first two appendages on the abdomen. An immature isopod will molt four to five times. These young isopods resemble the mature form of the isopod, with the exception of their small size in comparison to that of the adults. The juveniles molt in two stages. The back half molts first and then two or three days later the front half molts. This different molting can cause the coloration between the two halves of the isopod to differ. Nutritionally isopods are omnivores or scavengers who feed on decaying or dead plants and animals. Because Isopods breathe with gills, they can only live in areas that have high humidity, such as under rocks and logs, in leaf litter or in crevices. Some species are nocturnal. Their predators consist of both vertebrates and invertebrates. Like other animals, isopods such as pillbugs exhibit their own interesting behaviors. When disturbed, some species will roll up into a ball. They walk fairly quickly, even walking over one another. Environmentally, isopods have both positive and negative effects. The positive impacts of isopods include, within their immediate surroundings, a minimal amount of soil improvements. Unfortunately, large populations of these isopods can eat and damage the plants in greenhouses and southern states. Some of these interactions and descriptions of these isopods is clear from just observing them. These isopods, as well as other animals, exhibit many types of response to sensory input, a response that is known as behavior. The study of an animals behavior is called ethology. Two simple categories for behaviors are learned and innate (inherited). The behaviors that an animal uses to place itself in its most favorable environment are known as orientation behaviors. When the animal is stimulated by such things as light, heat, moisture, sound, or chemicals, they often exhibit taxis, with is the animals movement toward or away from a stimulus. In contrast to this is kinesis, which is a random movement that does not lead to orientation with respect to a certain stimulus. Another type of animal behavior is called agnostic behavior. This type of behavior is exhibited when animals respond to one another with aggressive or submissive response. It is often the case that these agnostic behavioral displays are a method of asserting dominance. Animals also have specific rituals and sets of activities that are involved in finding, courting and mating with another member of its species. Such activities are known as mating behaviors. Pillbugs exhibit, even just when being observed, many of these behaviors. One, the agnostic behaviors, involves the larger isopods appearing to fight. Soil conditions have various pHs. Some plants grow best in acidic conditions, whereas some grow best in basic conditions. Most, however, grow best in areas where the pH ranges from 6.5 to 7.2, 7 being neutral. Hydrochloric acid, HCl, (0.1 M) has a pH of about 1.1 and Potassium Hydroxide, KOH, (0.1 M) has a pH of about 13.5. These two chemicals exhibit pHs at the extremes of the pH scale. Detritus, on which isopods feed, has a more acidic pH. When organic matter decays, H+ ions are produced, thus adding acid to the soil. The acidity limit for plants tends to be no lower than about 4.5 to 5.6 on the pH scale. The vapor pressure of a liquid refers to the concept that the process of evaporation, in a closed container, will proceed until the number of molecules returning to the liquid is equal to the number of molecules that are escaping. When this equilibrium, the vapor is called saturated and the pressure of that vapor, which is normally expressed in mmHg, is referred to as the saturate d vapor pressure. The vapor pressure of HCl is the about the same as water, which is approximately 20 mmHg at room temperature, 22 C. The vapor pressure of KOH is about 2 mmHg for a 45% KOH solution.5 The purpose of this experiment was to use pillbugs to examine animal behaviors, such as taxis, to examine habitat preferences, and determine whether these isopods prefer moist or dry habitats, dark or light habitats, and acidic or caustic environments. It is hypothesized that, given that pillbugs posses gills, for which moisture is needed to help function properly, the pillbugs would prefer moist over dry environments. In addition, it can be hypothesized that, given that the pillbugs live under rocks and feed on decaying organic material, which releases acid into the soil, they would prefer the dark rather than light conditions and the acidic over the caustic environment. Materials and Methods Water Pipet Filter Paper (2 pieces) Choice Chamber Scissors Soft Brush 10 Pillbugs Stopwatch To observe pill bugs and their preference for moist versus dry conditions, a choice chamber, consisting of two petri dishes connected to one another, was obtained and lined with filter paper. Two pieces of filter paper were cut to fit the chambers. One was then moistened, using a pipette, with a few drops of water. The second piece of circular filter paper was left dry. The moistened filter paper was placed at the bottom of one chamber, chamber 1, and the dry filter paper was placed at the bottom of the other, chamber 2. Then, using a soft brush, ten pillbugs were obtained from the stock of pillbugs, and then placed into the chambers. Also using a soft brush, five pill bugs were placed in the dry chamber while the remaining five were placed in the moist chamber and the chambers were closed. This pillbug count for each chamber was then recorded for time zero minutes. Using the stopwatch to track time, the count of pill bugs on each side of the choice chamber was then recorded every 30 seconds for ten minutes, and continued even when some may no longer have been moving or were all on one side. Notes were taken on the actions and interactions of the pill bugs throughout the ten minute period. Once ten minutes had elapsed, the pillbugs were returned to the stock culture. Black Paper White Filter Paper Choice Chamber 10 Pillbugs Soft Brush Scissors Stopwatch To determine the preference of pillbugs between light and dark habitats and conditions, a choice chamber with two connecting petri dishes was lined with two different types of paper. One piece of normal filter paper and one piece of black paper were both cut to fit the chambers. Next, the bottom of the inside of one dish, chamber 1, was covered with the unaltered, white filter paper and the other dish, chamber 2, was lined with the black paper. Then, using a soft brush, ten pillbugs were obtained from the pill bug stock culture, five of which were placed in the black-paper lined chamber and the remaining five were placed in the white paper lined chamber. The choice chamber was then closed. The initial pill bug count, 5 in each chamber was then recorded in the table. For a period of ten minutes, using a stopwatch to track time, the count of the pillbugs on each side of the choice chamber was recorded every thirty seconds. In addition, notes about the interactions of the pill bugs were taken throughout the ten minute period. The count continued to be taken, regardless of the lack of movement from the pillbugs or the concentration of all ten in one chamber. After the ten minutes had elapsed, the pillbugs were returned to the stock culture. White Filter Paper (2 pieces) 0.1 M HCl (Hydrochloric Acid) 0.1 M KOH (Potassium Hydroxide) Pipettes (1 or 2) Filter Paper (3 Pieces) 3 Choice Chamber 10 Pillbugs Scissors Stopwatch To determine the preference of pillbugs in terms of basic versus acidic conditions, a 3-choice chamber was set up. Three pieces of filter paper were cut to fit the chambers. Using a pipette, about four drops of 0.1 M HCl were placed in a circular pattern about the paper. Another piece of filter paper was sprinkled with 0.1 M KOH in the same manner as was done with the hydrochloric acid. The HCl and KOH were applied to the filter paper in such a way that the paper was not drenched in the chemical. One chamber, the one connected to two other chambers was lined with an unaltered piece of filter paper. One of the two remaining chambers, chamber 1, was lined at the bottom (inside bottom) with the acidic filter paper and the remaining chamber, chamber 3, was lined at the bottom with the basic filter paper. Using a soft brush, the ten pill bugs were all removed from the stock culture and placed in chamber 2, the middle chamber consisting of the unaltered paper. The chambers were then covere d and the pillbug count was recorded in the table for the initial time of 0 minutes. For the next ten minutes, the count of pillbugs in each of the three chambers was recorded every thirty minutes. The data continued to be collected even when they were no longer moving between sides or were all on one side. After the ten minutes had elapsed, the ten pillbugs were returned to the stock culture. Results Table 1: Number of Pillbugs in Wet vs. Dry Chambers at Various Times Time (min.) Number in Wet Chamber Number in Dry Chamber Other Notes 0 5 5 Begin moving instantly 0.5 2 8 Large number shifts together to one side 1 1 9 One more baby follows 1.5 3 7 Fighting between two larger isopods 2 5 5 Even out again 2.5 5 5 Move about but come back to even; one not moving 3 6 4 More to wet chamber 3.5 4 6 Back to Dry Chamber 4 5 5 Crawling on underside of paper 4.5 4 6 Fighting to get from one side to another 5 3 7 Large pillbug still not moving 5.5 6 4 Other pillbugs begin gathering around non-moving pillbug 6 7 3 Pillbugs piled on top of one another 6.5 5 5 Pillbug begins to move again 7 4 6 More to Dry Chamber 7.5 5 5 Back at even 8 6 4 Continual switch from chamber to chamber 8.5 7 3 Begin gathering at wet chamber 9 9 1 More join wet chamber 9.5 7 3 Crowded, a few go to dry chamber 10 9 1 Return to wet chamber Table 2: Number of Pillbugs in Lighter vs. Darker Colored Chambers at Various Times Time (min.) Number in Light Chamber Number in Dark Chamber Other Notes 0 5 5 Begin moving instantly 0.5 3 7 Move to dark side 1 2 8 More to dark side 1.5 2 8 Remain, no overall movement 2 2 8 No overall movement 2.5 3 7 Begin going to white side 3 3 7 No overall movement 3.5 4 6 Moving to lighter side 4 2 8 Move to dark side 4.5 5 5 Equalize again 5 3 7 Fighting to get to dark side 5.5 5 5 Equalize again 6 4 6 More to Dark side 6.5 7 3 Piling up to get to lighter side 7 7 3 No overall movement 7.5 8 2 More in lighter side 8 9 1 More in lighter side 8.5 7 3 Move to dark side 9 5 5 Equalize again 9.5 3 7 Move to darker side 10 4 6 Young follows adult to other side Table 3: Number of Pillbugs in Neutral, Acidic and Basic Chambers at Various Times Time (min.) Number in Neutral Chamber (Control) Number in Acidic Chamber Number in Basic Chamber Other Notes 0 10 0 0 Immediate Movement 0.5 2 5 3 Move to acidic 1 3 5 2 Stay around outside of chamber 1.5 6 2 2 Quickly out of acidic and into neutral area 2 4 3 3 More to basic area 2.5 5 2 3 Away from acidic area 3 2 3 5 More slowly moving to basic area 3.5 2 1 7 Movement to basic chamber 4 4 0 6 Pillbugs all out of Acidic area 4.5 1 1 8 Most in Basic area 5 1 4 5 Some return to acidic chamber 5.5 3 1 6 Slowly moving out of Acidic chamber and into neutral and basic chambers 6 4 1 5 Out of basic and into neutral 6.5 3 1 6 Back into basic area, around outside of filter paper 7 3 1 6 No overall movement 7.5 4 0 6 All gone from acidic area 8 3 0 7 More to basic area 8.5 4 0 6 Small shift 9 3 0 7 Reverse of shift 9.5 2 0 8 More to basic area more slowly than before test 10 1 0 9 More to basic area Figure 1: Fluctuation in Number of Pillbugs in Wet and Dry Chambers Figure 2: Fluctuation in Number of Pillbugs in Lighter and Darker Colored Chambers Figure 3: Fluctuation in Number of Pillbugs in Acidic, Neutral and Basic Chambers Discussion Table 4: Average Number of Pillbugs in Wet vs. in Dry Chambers Time (min.) Number in Wet Chamber Number in Dry Chamber Average # of Pillbugs in Wet Average # of Pillbugs in Dry 0 5 5 0.5 2 8 1 1 9 1.5 3 7 2 5 5 2.5 5 5 3 6 4 3.5 4 6 4 5 5 4.5 4 6 5 3 7 5.5 6 4 6 7 3 6.5 5 5 7 4 6 7.5 5 5 8 6 4 8.5 7 3 9 9 1 9.5 7 3 10 9 1 Total # of Pillbugs 108 102 5.143 4.857 Table 5: Average Number of Pillbugs in Lighter vs. Darker-Colored Chambers Time (min.) Number in Light Chamber Number in Dark Chamber Average # of Pillbugs in White (Light) Average # of Pillbugs in Dark 0 5 5 0.5 3 7 1 2 8 1.5 2 8 2 2 8 2.5 3 7 3 3 7 3.5 4 6 4 2 8 4.5 5 5 5 3 7 5.5 5 5 6 4 6 6.5 7 3 7 7 3 7.5 8 2 8 9 1 8.5 7 3 9 5 5 9.5 3 7 10 4 6 Total # of Pillbugs 93 117 4.429 5.571 Table 6: Average Number of Pillbugs in Neutral, Acidic and Basic Chambers Time (min.) Number in Neutral Chamber Number in Acidic Chamber Number in Basic Chamber Average # of Pillbugs in Neutral Chamber Average # of Pillbugs in Acidic Chamber Average # of Pillbugs in Basic Chamber 0 10 0 0 0.5 2 5 3 1 3 5 2 1.5 6 2 2 2 4 3 3 2.5 5 2 3 3 2 3 5 3.5 2 1 7 4 4 0 6 4.5 1 1 8 5 1 4 5 5.5 3 1 6 6 4 1 5 6.5 3 1 6 7 3 1 6 7.5 4 0 6 8 3 0 7 8.5 4 0 6 9 3 0 7 9.5 2 0 8 10 1 0 9 Total # of Pillbugs 70 30 110 3.33 1.429 5.238 Figure 4: Comparison of Average Number of Pillbugs in Wet Chamber vs. in Dry Chamber Figure 5: Comparison of Average Number of Pillbugs in Lighter-colored and Dark-colored Paper Figure 6: Comparison of Average Number of Pillbugs in Acidic, Neutral and Basic Chambers It was hypothesized that the isopods (pillbugs), given their possession of gills for respiration and that they live underneath rocks and logs, places where light is not in abundance, would prefer the wet chamber over the dry chamber and the dark chamber over the light chamber. It was also hypothesized that, considering that the pillbugs feed off of decaying organic material, which in the process of decaying increases the acidity of the soil, these isopods would prefer the acidic chamber (the one with HCl), over the caustic (with KOH) and neutral chambers. The data collected from preforming the experiment partially supports the hypothesis. The average number of pill bugs in each chamber, was calculated by summing the pillbug count for all twenty-one times in one chamber and then doing so for the next and then dividing these totals by the total number of pillbugs counted. In each case this number was 210. The results show, as seen in Table 4 and Figure 4, that the average number of pil lbugs in the moist chamber over ten minutes was about 5.143 while the average number in the dry chamber was about 4.857. This higher average for the moist chamber illustrates taxis with a movement toward the stimulus of moisture. The second portion of the hypothesis was also supported by the data collected. Table 5 and Figure 5 both show that the average number of pillbugs in the chamber with white filter paper was about 4.429, in comparison to the average number in the chamber with dark paper, which was about 5.571. These results are consistent with the known habitat of isopods such as pillbugs. The hypothesis for third portion the experiment, however, was not supported by the data collected. Table 6 and Figure 6 both show that the pillbugs actually prefer a basic environment, one with drops of KOH, over an environment with no chemical additives and the environment with the addition of drops of the strong acid HCl. The average for the number of pillbugs in the neutral environment w as about 3.33, for the acidic environment the average was 1.429 and for the caustic environment the average was about 5.238. These results could possibly be explained by the higher vapor pressure of HCl in comparison to that of the KOH. With a higher vapor pressure, the HCl would have vaporized more easily and quickly, thus getting into the gills of the pillbugs and causing them irritation. This irritation would explain their clear lack of fondness for the HCl permeated filter paper. The lack of pillbugs accumulating on the plain filter paper can possibly be explained by its complete lack of moisture, and that the antennae on the pillbugs would not sense any chemical or something of that nature, that would attract the pillbugs to that chamber. The interaction of the pillbugs inside the choice chambers is indicative of agnostic behavior, as seen in the fighting of the pillbugs. Human error, such as counting, would not play any, or any significant role, in the results of the experimen t. This experiment and the results obtained from it support most of the hypothesis, but conflict with and not support another portion. The results support the preference that pillbugs have for moist and dark environments, but suggests that pillbugs prefer more caustic environments to neutral and acidic environments. Citations