Rise of the flies: Temperature and Movement

Rise of the flies : Quantifying flies movements at different temperatures

DrosobluZ is a  one week project made by three student in the frontiers of life sciences bachelor ( university Paris Descartes). This project had been realized during a program called “Biosensors” in which student learn through scientific research project about how organisms can sense their environment.

Have you ever heard about the fascinating particularity of Drosophila melanogaster  that intuitively move through the opposite gravity direction ? This characteristic is called “negative gravitaxis” :  “negative” for “opposite to”, “Gravit” for “gravity” and “taxis” for “turning toward”.  

FYI : the tube on this gif has a diameter of 19mm (duration : 5.40 seconds)

The aim of our project was to study the relationship between the media temperature and the flies speed 
while they were climbing a tube of glass. Drosophila melanogaster is a common insect found used extensively in genetic studies. Why did we choose to use Drosophila melanogaster as model organism for our experiment ? Negative gravitaxis ensured that whatever the conditions of the fly, simply turning the tube upside down would insure an observable movement.

A simple protocol but not so easy to implement :

We choose to study three different temperatures not so far from the Drosophila optimal growing temperature (29°C) so we don’t hurt them. For this, we used a cold temperature at 8.5°C, a room temperature at 20°C and a hot temperature at 29°C. To expose  the flies to these temperatures, we proceeded by putting them in glass tubes, in different bain-marie. After 3 minutes of bain-marie, we took the tube and tapped it gently on a soft surface in order to put all the flies at the bottom of the tube. Now we were assured that they would be climbing the wall to go to the top of the tube. Why ? …….Yes, you have well understand : negative gravitaxis!!

Each tube was then put to a power nap of 10 minutes in an ambient temperature before being exposed again to another temperature. Finally, each tube is exposed to the three different temperatures. We realized  that even with the “resting” time, our flies population could have different move speed depending on the previous incubation. Indeed, it may be that the temperature imposed caused an irreversible impact on their body. To prevent this bias, we choose to do different temperature combinations with different population in different tubes. We also decided arbitrary that the flies could only be affected by  the previous temperature. In your opinion, how many tube did we needed to have all the possible combination ?

We need four different tubes in order to conserve all the possible combinations.

Unfortunately, these combination prevent us to analyse the four tube together because we can’t assume that these populations had the same conditions.

We shot the flies motion in the tube after taping them during 10 second.

To analyse the flies speed, we used a software called ImageJ, which allows us to track the flies positions each half second (so each fifteen frames). We could convert the pixel distance of the video to a mm distance by using the tube diameter (16 mm). With the tracking, we can access to the distance between each frames. With these distance and the time information ( the 10 second of our chronometer ), we could determine a speed for each flies of every tube at every temperature.

Results :

This figure presents the speed of the flies according to the different temperature.

We observes two global tendencies. First, when the temperature increases, the flies move faster. Secondly, the speed variation between the flies augments with an increasing temperature. It means that at a cold temperature, the flies globally go to the same speed while at a hot temperature, all the flies have  different speed : their speed are not homogeneous anymore. However, this experiment should be done again with a bigger sample of flies, in order to prove the reliability of these results.

To conclude, the fruit flies seem to posses a temperature sensor triggering a motion behaviour. A cold temperature slow them while a hot temperature make them move faster. Indeed, an exposure to a very low temperature (-10°C) during one minute can trigger hibernation, which is defined by a slow metabolism.

Want to know more ?

• If you want to know more about these fascinating fruit flies Drosophila melanogaster and the big impact they had on the scientific discoveries, this is a nice video : https://www.youtube.com/watch?v=qDbJnFLl3kU

• Check out the Storify of this amazing project :
  https://storify.com/DinobluZ/from-dinobluz-to-drosobluz/preview

• If you want to see which physiological and genetic pathway allow Drosophila melanogaster to sense temperature, you can check this scientific paper : http://www.sciencedirect.com/science/article/pii/S0306456502000578 ( Hoffmann, Ary A., Jesper G. Sørensen, and Volker Loeschcke. "Adaptation of Drosophila to temperature extremes: bringing together quantitative and molecular approaches." Journal of Thermal Biology 28.3 (2003): 175-216.)