Blue light intensity variation: How do Daphnia and electronic sensors react to it?
Team members: Tanguy Chotel, François Sacquin, Sarah Talon Sampieri
Are electronic sensors really better at their functioning, considering they are conceived by inspirations of biological mechanisms? Is computer really powerful compared to human brain? What are its limits and what are its strengths? We tried to focus our research on this questionings this week, taking light sensors as our term of comparison.
Daphnias, that are little crustaces living in freshwater, are known to change their phototaxis, which is the movement of the organisms toward or against the light source, according to the increase of light intensity: the increase in intensity of light increases the movement downward of daphnias. Afterwards, we found that daphnias tend to have a vertical movement upward when exposed to blue light. We wanted to have an insight to this founding by changing one parameter: what does happens if we change the intensity of light? Do daphnia will keep this vertical movement? If yes, in what degree? If not, how will they behave?
Secondly, we will compare our findings in the reactivity to light of daphnia to the increase of blue light to the photoreactivity of electronic sensors, that, in our case, will be an arduino equipped with an intensity sensor and exposed to blue light. What is an Arduino ? check THIS out !
Description of the image: Daphnia pulex, one of the two easily available species that can be found in nature. The other one is called Daphnia Magna, and it generally looks like a little bit bigger in size than Daphnia pulex.
Here is a really cool video about Daphnia doing upward movement when exposed to blue light, and going downward when exposed to red light !
Biological Experiment
As we wanted to test how daphnia reacted to the variation of intensity of blue light, we exposed our populations to eight different intensities of light from 30 arbitrary unit(a.u) to 240a.u, in 8 steps. This was made by putting an arduino with a blue led on each beaker, and recording videos for each intensity of light.
To have as many data possible and do an accurate data analysis, we did the same experiment with 3 different populations, 3 times each. Between each recording, we made sure to reset to standard conditions of the experience by waiting 30s of dark before starting with the new intensity of light. (In order to do that, we did all our experiments under a cardboard ! to simulate a “Dark Room”.
Finally, we measured the distribution of daphnia in the beakers depending on the variation of blue light intensity by compartmentalizing the beaker from level 0 to level 4, starting from the bottom to the top. This allowed us to count how many daphnia were present for each level in each video.
Arduino Experiment
For the Arduino part, we made the exact same thing but switched the beakers with the electronic intensity sensor. The intensity perceived by the sensor were directly converted and analysed to get these awesome graphs describing the intensity perceived over the intensity given.
On the graph above, we study how a population of 23 Daphnia evolves spatially under different blue light intensities. In order to better graph our data, we represented our population over time through differential populations. Each point is the population in a section after 30 seconds of light exposure subtracted by the same section population after 10 seconds. Thus, a point above the zero line indicates an increase.
For the electronic sensor, we noticed that the photo-resistor was very accurate for detecting light intensities but its range was very unpredictable due to calibration problems that affected all sensors.
Conclusion
We thus concluded that electronic sensor can be precise and accurate but have to be scaled
back by a function to real light intensities due to range calibration. The biological sensors on the other hand did not end in any significant conclusion as Daphnia did not behave as we expected them to. Overall, this project could be further continued by studying the impact of other wavelength on the Daphnia and comparing as many sensors as possible to find the best possible function of transition intensity => lux.
If you want to know more, check out our full work !
Mail : Photons.unchained@gmail.com
Sources :
Daphnia:
Nédélec, François J. "Mechanism of phototaxis in marine zooplankton: Description of the model." (2008).
van Gool, Erik, and Joop Ringelberg. "The effect of accelerations in light increase on the phototactic downward swimming of Daphnia and the relevance to diel vertical migration." Journal of plankton research 19.12 (1997): 2041-2050.
Steams, Stephen C. "Light responses of Daphnia pulex." Limnol Oceanogr 20 (1975): 564-70
Ringelberg, Johannes. "The positively phototactic reaction of Daphnia magna Straus: a contribution to the understanding of diurnal vertical migration." Netherlands Journal of Sea Research 2.3 (1964): 319IN1335-334IN2406.
Arduino
http://www.mouser.fr/Search/ProductDetail.aspx?R=1384virtualkey54850000virtualkey485-1384
http://www.mouser.fr/ProductDetail/Adafruit/161/?qs=%2fha2pyFaduidPXPXSuFTA5DDZdShRkexJbM%2fC0FaJ9I2cgisBToc9Q%3d%3d
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