Synopsis

How Oxygen Kindles Fireflies

X-ray images of the light-emitting organs in fireflies clarify the mechanism by which oxygen controls the insects’ luminescence.

To communicate and find mates, fireflies produce light flashes through a luminescence process whose chemistry is well known: in the presence of oxygen, an enzyme acts on the compound luciferin (Latin for “light-bringer”), triggering an oxidation reaction that is accompanied by light emission. Determining the mechanism that regulates the oxygen supply has been difficult because the tracheal network that carries the gas to the light-emitting organs, known as photocites, has features as small as 100 nanometers (nm), finer than the resolving power of most microscopes. Now, Yeukuang Hwu at the Academia Sinica and the National Cheng Kung University, Taiwan, and co-workers have used tomographic and microscopy techniques with 20-nm resolution to image the insects’ organs and derive oxygen flux estimates that support a specific supply mechanism.

The researchers designed their experiment to test two leading hypothesis for the oxygen supply mechanism. The first revolves around the firefly’s production of nitric oxide (NO) inside the photocites: before a flash, the gas soaks the mitochondria—organelles that, fed by oxygen, control energy production in cells— suppressing their activity and leaving extra oxygen available for bioluminescence. The second conjecture proposes that circulating fluid in the tracheal network rises or ebbs to control oxygen. The authors’ experiments, carried out at Taiwan’s synchrotron light source, provided evidence for the first theory: x-ray images of the tracheal system in live insects showed no fluid inside the tracheal system. By measuring the tracheal geometries with high resolution, the researchers were able to estimate how much gas could diffuse from the tracheal network to tissues, yielding values consistent with the NO hypothesis.

This research is published in Physical Review Letters.

–Matteo Rini