This study had shown the average performance of the twenty Daphnia during light stimulation. The result indicate an obvious behavior where most of the Daphnia migrated to the right side of the Petri dish which was covered by the aluminum. There was a significant difference in the number of Daphnia appeared in the brighter side of the dish; as shown in the data analysis, 4. 33+1-1. 136 SD in the experimental group and 10. 72+/-1. SUDS for the control group. The results strongly suggest that the subject were avoiding the light by hiding in the shaded part of the dish.
The findings of this experiment support the conclusion of the research done by Gerhardt A. Et al (2006) in which the Daphnia had shown negative photovoltaic behavior. Introduction This experiment examine the behavior of the freshwater zooplankton, Daphnia magna, under the light. More precisely, the Photostats response of the subjects is the main concern of this paper. In order to explore further, we must understand that photovoltaic positive genotypes spend much time in the upper water level, whereas photovoltaic negative genotypes close to the bottom.
Because of their long reproduction, daphnia is a great subject to be used for quantitative genetic studies which contribute to the researches in evolutionary ecology. For nearly every trait that has been investigated, genetic variation has been reported. Examples include age and size at maturity, size at birth, vertical migration, photovoltaic behavior, fish escape behavior and many more (Bert, 2005). Dauphins have jumping like act while swimming, they have a migratory behavior, where they migrate to the bottom or the water during the day time and they migrate to the surface of the water at sunset.
This behavior is due to avoidance of visual predator such as juvenile fish (Bert, 2005). However in the absence of the fish the Dauphins still be on the bottom of the water this may probably due to avoidance on UP light (McLeod et al. 2011). In this experiment, the same subjects in two different lighting conditions was tested in order to observe the change in behavior of Daphnia under light. The controlled variables were light source; size of environment; same amount of subjects; time of sample collection, the light was set as a control variable, and thus it was always turned on during the length of the experiment.
On the one hand, the independent variable was the difference in the exposure to light with one side cover or uncover. One the other hand, the dependent variable was the numbers of Daphnia in the left side of the Petri dish. The difference between the control treatment and the experimental treatment is that the former is with the right side of the Petri dish uncovered and the latter is with the right side covered. In brief, the purpose of this experimental study is therefore to measure the photovoltaic behavior of Daphnia magna with the hypothesis that waterless do exhibit negative Photostats.
Analytically, the goal is to see if the null hypothesis, water fleas do not exhibit Photostats, should be accepted or rejected using a T- test. Based on the alternative hypothesis generated from previous researches, the prediction of this experiment would be that water fleas exhibit negative Photostats. This study would serve to support and reinforce the previous finding on the topic of the photovoltaic behavior of zooplankton and to possibly help in generating new hypothesis for future studies.
Materials & Methods The experiment was designed with respect to the ethical procedures of handling animals in laboratory experiment. Thus, the goal was to collect the data within a reasonable amount of time without exposing the Daphnia to the heat of the light for too long. Any possible harms to the subjects were kept strictly at the minimum level. Two to three students were teamed up to conduct this experiment. The sole purpose of the latter is to determine the photovoltaic behavior in water fleas. To begin, using the black marker to draw a central line on the bottom part of the Petri dish.
Second, each team had to prepare the environment in which the behavior of water fleas will be observed, by filling the Petri dish with mall of chlorinated water measured using a mall graduated cylinder. Then, each team used a small pipette to carefully transfer 20 water fleas of similar sizes from the pool of water fleas to the prepared Petri dish (Note that 20 subjects were used in both treatments, i. E. Paired treatments). The light source, an incandescent light bulb (artificially light), was place right above the Petri dish.
By placing the dish on a white paper, the black central line which divides the dish in half can be seen much clearer. Once introduced into the new environment, the water fleas were given about a minute to acclimatize themselves. In the control treatment, to insure the precision of the date, three groups of six sub-trials were conducted. Each sub-trail was taken in intervals of 30 seconds using of a timer to maintain the consistency of the data collection. After every 6 trails, the dish had to be swirled gently to reset the experiment and given a minute of rest, allowing the subjects to acclimatize, before continuing with the next trail.
The goal was to observe and COUnt how many water fleas there were on the left side (always illuminated) of the dish in each trail. After completing the control experiment, i. E. 8 trials, the right half of the Petri dish was covered by a pre-cut piece of aluminum foil which set up for the experimental treatment. Under the same environment, the dish was half bright (left side uncovered) and half dark (right side covered). The data collection procedure is the same as in the control treatment. The number of water fleas appeared on the left side (lighten) of the dish was observed.
When one or many of them lay on the central line, they were still considered to be in the dark (right) side. Although with precaution and meticulous design, many uncontrollable factors eight still affect this experiment such as the heat emitted by the incandescent bulb, the noise that students were making, the health of every individual subject and so forth. Since thermometer was not provided, the exact variation of water temperature could not be measured between treatments. The size of water fleas were not exactly the same leaving the possibility that the degree of sensitivity to light might differ depending on their developmental stage.
Finally, the artificial light is different than the Sun light which has a larger spectrum. This might have an effect on the behavior of the subjects because they react differently under pacific ranges of wavelength (Store & Paul, 1998). Results The collected data suggested that a larger number of water fleas chose the darker side over the brighter side of the dish. The difference between the means of control treatment and the experimental treatment were significant enough to support the existence of positive or negative photolytic behavior in Dauphins. Figure A. [Comparison between the control and experiment treatments]. Appendix 2) The mean percent of Daphnia on the left side of the Petri dish when the right side was covered (4. 333/20. 0 x 100% = 21. 7%) was significantly lower than the mean percent of Daphnia on the left side when the right side was uncovered (10. 72/20. 0 x 100% = 53. 6%). The difference in means shown in Figure A is statistically significant to represent the true difference in the effect of the independent variable (right side of the dish uncovered vs… Covered) on the dependent variable (number of water fleas on the brighter side of the dish) and not due to luck or chances.
The full t-test procedure and calculations are documented in Appendix 3. The test was conducted to decide whether or not to reject the null hypothesis which stated that water fleas do not exhibit Photostats at all. The 1 -tailed alternate hypothesis suggested that water fleas exhibit negative Photostats, in other words, the majorities of the subjects would move into the darker side of the dish. The alpha level used was “a = 0. 05” meaning at 95% confidence level the true sample mean falls within the interval. The t-value= 13. 026 was calculated using excel. Appendix 3) With a degree of freedom of 17 (18-1) and a = 0. 05 for I-tailed, the critical t-value yields at 1. 74 by looking up in the table oft-test (Appendix 1). By comparison the calculated t-value (13. 026) is much larger than the critical t- value (1. 74). Hence, the null hypothesis shall be rejected while accepting the alternative hypothesis which supports the negative photolytic behavior in water fleas. Discussion This study was conducted by measuring the average performance of the twenty Daphnia during light stimulation.
When the right side of the dish was covered by the aluminum foil, the Daphnia migrated to the right side (darker) of the dish. A significant difference in the number of Daphnia appeared on the left side (brighter) was found to be 4. 33+/-1. 136 SD in the experimental treatment comparing to 10. 72+/-1. SUDS in the control treatment which strongly suggests hey were avoiding the light by hidden in the shaded part of the dish. This result is similar to the finding on the research done by Gerhardt A. Et al in their paper: Automated Recording of Vertical Negative Photovoltaic Behavior in Daphnia magna Straus (Crustacean) in 2006.
In alignment with the hypothesis of this study, the negative photovoltaic behavior of the Daphnia can be further explained through the defense mechanism of Daphnia towards potential predator. The shaded part of the dish represented a safer environment in which they are less prone to be attacked by predators who seek for prey in a brighter lighted environment. Another possible suggestion was that the artificial light can be recognized as of the sun. Daphnia goes to the deep part of the water during the day and they appear in the upper part after sunset (Bert, 2005).
The heat produced by the sun might change their body temperature since most invertebrates are exothermic which means their internal temperature is influenced by external sources (Campbell, 2011). They could be trying to avoid this external heat by hiding under the covered part of the dish. As in most studies, some limitations reside in the subject, the materials and the environment using to conduct this experiment. First, only a small sample size of twenty Daphnia was use for this experiment and they were not at the same developmental stage.
Although the result was already quite significant, using a larger quantity of similar sizes of Daphnia would improve the precision and accuracy of this study by reducing the margin errors. Second, given the artificial light source, the change in the temperatures of the incandescent light may affect the result of this experiment. The photovoltaic behavior of the subjects might also vary according to the wavelength ranges of the light source and its intensity (Store & Paul, 1998). Third, the environment was not ideal in terms of noise reduction which might affect the subjects’ behavior as well.
Finally, the concept of gestates were not explored in the study and the environment (a flat Petri dish) was not set to test for egotistic responses, i. E. An organism’s response towards to away from the gravitational force, which would possibly alter Daphnia behavior on its own (Grosser et al. 1953). In conclusion, through the results of this study, Daphnia Magna is shown to exhibit negative Photostats which can be explained by their predator avoidance mechanism. References Bert D. Ecology, 2005. Epidemiology, and Evolution of Parasitism in Daphnia [Internet].