LABORATORY REPORT Positive chemotactic response of pillbugs (Armadillidium sp) to moisture

Abstract.  The behavioral response of the organisms to certain chemical in the environment provides information on the optimal conditions on the growth and development of a certain species (Olanga et al., 2010).  The chemotactic behavioral response of the pillbug (Armadillidium sp.) was determined through its exposure to dry and moist environments.  The pillbug was observed to direct their movement towards the moist environment.  On the hand, the addition of honey to a moist environment generated a negative behavioral response from the pillbugs.  The experiment shows that the pillbug has the capacity to detect any changes in its immediate environment, as well as respond to such factors through migration.

Introduction.  Ethology pertains to the study of animal responses to various stimuli, which may be chemical, physical or biological in nature (Gherardi, 2009).  The behavior of a species organism, namely the pillbug (Armadillidium sp.) was investigated in order to determine its actual response to a specific condition.  Pillbugs are crustaceans that are predominantly terrestrial.  The mode of locomotion for pillbugs is mainly through the use of approximately seven pairs of segmented legs or appendages.  For respiration, pillbugs are equipped with gills, which exchange gases through the cell membrane.  Pillbugs have two pairs of antennae for sensing their immediate surroundings.  It has been established that pillbugs live in moist places and are predominantly nocturnal.  Upon exposure to a stressful condition, pillbugs are known to roll their bodies into a ball.

In this study, pillbugs were used as animal models because they are easy to handle, based on size and general activities.  In addition, the behavior of pillbugs is simple to detect, as these animals roll into a ball when in the presence of stress or stimuli (Wu et al., 2010).  Two hypotheses would be tested in the study, namely, Pillbugs prefer moist environments, and that Pillbugs prefer only water in their moist environment.    

Methods.  Baseline information on pillbug behavior was collected before the actual experimental study.  Firstly, a pillbugs position based on the angle of the cylinder was determined.  Secondly, the speed of movement of a pillbug from one site to another was measured in terms of distance (in millimeters) and time (in seconds).  In another setup, two petri dishes were connected to each other, with a passageway between each dish.  One petri dish contained a wet filter paper, while the other petri dish contained a dry filter paper.  Approximately 4 pillbugs were placed in each dish and allowed to acclimate for 5 minutes then observations were performed for the next 10 minutes.   The t-test was performed to analyze the data collected.

In the actual experiment, the control setup consisted of water vs dry conditions, while he experimental setup consisted of water vs water and honey environment.     Approximately 6 pillbugs were placed in each setup and the positions of the pillbugs were monitored every minute for a total of 5 minutes.

Results.  The preferred direction of motion of each pillbug was upwards and towards the top of the cylinder when the angle of the cylinder was horizontally flat.  The pillbug stayed at the bottom of the cylinder when the container was at a slight, steep or even vertical angle.  Based on the observations of 4 pillbugs, the average speed of the pillbug was calculated as 0.07 mmsec.  The pillbugs were also observed to prefer the moist petri dish (Mean moist  4.1, dry  3.9 SD  moist  0.63, dry  0.74).  The t-test resulted in a P value of 0.3419, showing that the difference between the two groups was not statistically significant.  In addition, t  0.9762, df  18 and the standard error of difference  0.307.  

The two trials of the actual experiment generated statistically significant data, as presented in Table 1
 Table 1.  Average behavioral responses of pilllbugs to environments supplied with water or water with honey.  
           
TrialMoist (Control)Dry
(Control)Moist
(Water)WaterHoneyTrial 142.84.21.8Trial 23.62.441.6

The P value of the first trial of the moist vs dry assay generated a two-tailed P value of 0.4714 (not significant).  In addition, the mean of moist minus dry was equal to 0.40.  The t value was determined to be 0.7559, df  9 and the standard error of difference  0.529.  The P value of the second trial of the moist vs dry assay generated a two-tailed P value of 0.0085 (highly significant).  In addition, the mean of moist minus dry was equal to 1.20.  The t value was determined to be 3.4641, df  8 and the standard error of difference  0.346.  
 
The P value of the first trial of the water vs water  honey assay generated a two-tailed P value of 0.0019 (highly significant).  In addition, the mean of moist minus dry was equal to 2.4 (mean water  4.2, water  honey  1.80 SD water  0.84, water  honey  0.84 SEM water  0.37, water and honey  0.37).  The t value was determined to be 4.5356, df  8 and the standard error of difference  0.529.  The P value of the second trial of the water vs water  honey assay generated a two-tailed P value of 0.0021 (highly significant) and the mean of moist minus dry was equal to 2.00.  The t value was determined to be 4.4721, df  8 and the standard error of difference  0.447 (mean water  4.00, water  honey  2.00 SD water  0.71, water  honey  0.71).  

Discussion   The baseline information collected from the study allowed the researcher to determine the normal conditions of living for the pillbug bug.  The pillbug often stays at the bottom of the graduate cylinder when the cylinder is positioned upright or at an angle.  However, the pillbug starts to migrate towards the opening of the cylinder when the cylinder is positioned in a vertical fashion.  The speed of pillbug migration has also been determined to be at an average of 0.07 mmsec.

The experiment showed that the pillbugs preferred moist environments over dry environments.  In addition, the pillbugs preferred a moist environment that simply contains water and no other chemical.  The observations are statistically supported by significant P values.  The experiment showed that the pillbugs migrated towards the petri dish that only contained water and avoided the petri dish that was supplied with a filter paper moistened with water and honey.  One obstacle to the experiment was the width of the opening between the two petri dishes, as this might not have been wide enough to allow the pillbugs to freely move around during the experimentation.

The observations collected from the study showed that pillbugs prefer moist environment that do not contain any other chemical reagent.  The study thus proves that the hypothesis that  Pillbugs prefer moist environments, and that Pillbugs prefer only water in their moist environment are correct.

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