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Groundbreaking Research Uncovers the Biological Mechanisms Fireflies Use to Emit Light
The mechanism by which fireflies emit light has long been an unsolved mystery in the biological sciences. However, in a recent study, researchers at NTHU’s Institute of Molecular and Cellular Biology working in conjunction with researchers at Academia Sinica’s Institute of Physics used synchrotron phase contrast micro tomography and transmission x-ray microscopy to observe the biological mechanism by which these fascinating insects produce light.
 
Some time ago scientists succeeded in identifying the enzyme by which various insects produce light, and then went on to extract and synthesize it for use in a wide variety of applications. However, fireflies are unique in their ability to control their glow and use it for mating and communicating with one another.
 
According to Tsai Yueh-Lin, the lead author and a 2012 graduate of NTHU’s Master Program in molecular and cellular biology, until recently there were two main theories for explaining the mechanism by which fireflies control the rate at which they flash: 1) Fireflies use their highly efficient tracheal system to simultaneously supply a sufficient amount of oxygen to their light-producing cells as well as the mitochondrion and the fluorescence mechanism; and 2) Prior to flashing, the amount of oxygen consumed by the mitochondrion is reduced in order to have enough oxygen for the fluorescence mechanism. In order to test these two theories it was necessary to first gain a sufficient understanding of the efficiency with which the firefly’s tracheal system supplies oxygen. According to the former theory, since the oxygen supply is more than sufficient, there is no need to consider the possibility of the mitochondrion and the fluorescence mechanism competing for oxygen. According to the latter theory, the firefly’s tracheal system is unable to simultaneously supply enough oxygen to both the mitochondrion and the fluorescence mechanism.
 
Using the traditional methods of biological research to study a live insect, it wasn’t possible to carry out a real-time imaging analysis with a sufficiently precise dot per inch (DPI) level, making it impossible to test these two theories. To solve this problem, the research team used synchrotron phase contrast micro tomography and transmission X-ray microscopy to obtain a three-dimensional image of the firefly’s flash mechanism, including the highly complex structure of its tracheal system and its bronchial tubes, which are less than 200 nanometers in diameter. After quantifying the results, it was possible to precisely calculate the rate at which oxygen flows to the light-producing cells and the amount of energy they consume. Based on this data they then estimated the overall efficiency of the mechanism by which the oxygen is supplied and consumed.
 
Having already confirmed the relationship between the mitochondrion and the duration of the luminescence, it was possible to infer that under normal metabolic conditions, when all the oxygen supplied by the tracheal system is consumed by the mitochondrion, then no oxygen would be available to enter into the illumination system. They found that the flash rate depends on the deactivation of the mitochondrion, as demonstrated by using nobelium to suppress the action of the mitochondrion, which resulted in a flash due to oxygen being made available to the illumination system.
 
In addition to Tsai, the research team included Professor Li Chia-Wei (Tsai’s academic advisor), Hong Tzay-ming of NTHU’s Department of Physics, Hwu Yeu-Kuang of Academia Sinica’s Institute of Physics, and several researches from the Endemic Species Research Institute in Nantou County and the Faculté des Sciences de Base, Ecole Polytechnique Fédérale de Lausanne in Switzerland. The research took over one year to complete, and the results have been published in the prestigious journal Physical Review Letters (DOI: 10.1103/physrevlett.113.258103).
 
Describing the research carried out while he was still completing his Master degree, Tsai states, “We had to try out a wide variety of possible solutions. We also had to continually overcome our own limitations.” Corresponding author Li Chia-Wei commented that he is proud that one of his students has successfully conducted such painstaking and fruitful research, and that such an interdisciplinary approach is the best way to solve difficult problems.
 
 The tracheal system of a firefly as seen through synchrotron phase contrast micro tomography and transmission X-ray microscopy.

The tracheal system of a firefly as seen through synchrotron phase contrast micro tomography and transmission X-ray microscopy.

Lead author Tsai Yueh-Lin (right) and contributing author Hsu Su-Ting, both graduates of NTHU’s Institute of Molecular and Cellular Biology.

Lead author Tsai Yueh-Lin (right) and contributing author Hsu Su-Ting, both graduates of NTHU’s Institute of Molecular and Cellular Biology.

 

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