The fantastic battle: Tardigrada versus the machine
Today, sensor is synonymous of electric machine. However, did you ever notice that flowers follow the sunlight? That the human’s pupils react to them? These points show that living being can have some similarities with an electric sensor.
But how much efficient can be a biosensor compare to a machine? Can we use an organism to indicate the intensity of light? What about Tardigrada the amazing organism who can live in space?
Our experiment gives the floor to Tardigrada (or water bears), these wonderful and cute animals. Thus, we bring face to face
light-sensor. Which sensor is the best? The most reactive to light intensity?
Drawing of the biosensor manipulation
But how can we compare a bio and electric sensor? Our protocol is simple: put them in dark condition first and light them up. More precisely, for the biosensor, we prepared a slide with Tardigrada on an agar pathway. Then, we put it on the microscope. To isolate the microscope from the ambient light, we protect it with a dark plastic bag. While the bag is ready, we light the slide. The light intensity is our variable. The intensity of light starts at 0 (so no light) to 255 (the highest brightness). 0 is our negative control. If no reaction appends at this intensity, water bears wouldn’t have a reaction to light. A contrary, 255 is our positive control. If there are no reaction while it was expected, our basic hypothesis could change or be wrong. Indeed, according to literature, Tardigrada should go faster in the dark than in the light³.
In the electric sensor case, the principle is the same. Except that we put the sensor directly in the bag, in front of the light. We respected the same distance from the light than for the biosensor, which is a slide.
With this method, we obtain the speed of the water bears and the intensity perceived by the sensor. Why water bear's speed could help us to understand their reactivity to light intensity variation? We hypothesize that they go faster with a lower intensity, thank literature³. However, our results show a different tendency. Look at the graph opposite, do you notice a logical response to intensity? For instance, the difference in speed is not significant between 0 and 10 intensity. Moreover,
the speed variation of each intensity
is high. Thus, the precision of our
results is low.
For the sensor, the link between the intensity of the light and the intensity perceive by the sensor is clearer. As you can see below, we observed that the intensity perceived by the sensor at 0 intensity is less important than at 255. Moreover, this one increased with the intensity of the light while it was not the case with Tardigrades. An interesting fact is the error bar. The error bars indicate the difference between the minimal and the maximum data (it is the dotted line). We can notice that for a low intensity, the error bar is less important than for the highest intensity. In other words, the precision of the sensor is better for low intensities!
To sum up, can we use a Tardigrades as a light sensor? It seems not. Our results show that Tardigrades didn’t respond to light as it was expected. There is no significant tendency about the Tardigrades’ speed between the intensities. However, don’t be disappointed! Our method could be improved in order to make another experiment in better condition. As we said before, we used a dark plastic bag to isolate the sensor from the light. Which is not ideal because according to the moment of the day of the place where we did the manipulation, the result can change. The bag is not enough opaque to be an efficient isolator. Then, in our slide, there is food for Tardigrades. But, water bears are guzzler! They eat and are focused on eating. Thus, this could be a bias that changes the behavior of the Tardigrade light response. Furthermore, they didn’t have the same size and shape. So, it was difficult to compare their speed between them. A bigger Tardigrade could go faster than a tiny one.
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| Wikipedia.com |
Thus, even Tardigrades seem to not be practical as a light sensor, they are alway full of secret! If you want to know more about them (in order to go further in our experiment for instance …) check this link:
- http://www.wikihow.com/Find-and-Care-for-a-Pet-Tardigrade-(Water-Bear): to find and breed water bears
- https://www.youtube.com/watch?v=hpRwGREdv8A: a video because there are so cute when they are swimming!
- http://www.ctoz.nl/vol79/nr01/a02: Shcherbakov, D., Schill, R. O., Brümmer, F., and Blum, M. (2010). Movement behaviour and video tracking of Milnesium tardigradum Doyère, 1840 (Eutardigrada, Apochela). Contributions to Zoology 79, 33-38.
- https://storify.com/LightingLifeFdV/lighting-life: link to the storify of the project.
- https://github.com/learningthruresearch/Biosensors2017/tree/master/lighting_life: link to the GitHub (with all the resources) of the project.
By Léonie Ledrein, Nikola Zarevski, Nina Varchavsky
If you are interested and want to know more about it. Here is a link to our storify (https://storify.com/LightingLifeFdV/lighting-life#publicize) and to our documentation (https://docs.google.com/document/d/1fKswlKEbpzqJVpeedX4WCdezd20ilWIrg-Y5DvCmt9M/edit) containing more info if you want to replicate our experiment.
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