Shine Bright Like a Firefly

By Naiyerah Kolkailah

Have you ever met people who give off a strikingly radiant, warm energy? Ok, their bodies don’t physically light up, but they have really bright or charming personalities that make you drawn to them. Bring those people to mind, and smile!

As a biology lover, I’m intrigued by living organisms that produce and emit visible light. These are examples of beautiful plankton and mushrooms that light up the night.

This natural phenomenon, called bioluminescence, is found in many marine animals, fungi, bacteria and terrestrial invertebrates (i.e. insects).  The production of light can be used to communicate and attract mates, but it can also be used to confuse, distract, or ward off potential predators. Another tactic is using light to lure and draw in prey (remember that scary sea creature from Finding Nemo?). That was an anglerfish!

One of the most studied bioluminescent organisms is the firefly, especially the North American firefly (Photinus pyralis). These wondrous little critters (which are actually beetles) light up to communicate during biological courtship. Maybe you've chased them down as a kid, or seen them glowing and dancing through the night.

Have you ever wondered where their light comes from? How is it made? Let’s take a quick stroll into the dazzling world of fireflies.

If you look at the image above, you can see that only the lower part of the firefly’s body is lit up. That region, in the firefly’s abdomen, is called the “lantern.” It is composed of photocytes, which are the cells where light is generated.

Inside the peroxisomes of these cells, there is a compound called luciferin. In the presence of oxygen (and ATP), the enzyme luciferase catalyzes a reaction that oxidizes luciferin into oxyluciferin. Energy is released from that reaction in the form of light!

If you think of photosynthesis as converting light energy (photons) into chemical energy, this is a different biochemical process that does the opposite. What a brilliant biochemical reaction!

Now, you might be wondering where the oxygen comes from for this reaction; how is oxygen supplied to the photocytes that produce light? This topic is the subject of current research on firefly light flashing. In the lantern, there is an incredibly complex tracheal system in which the trachea branch into smaller tracheoles. These tracheoles are surrounded by the lantern’s photocytes. In the microimage below, you can see these larger trachea branching into smaller tracheoles.

It is these tracheoles that supply the photocytes with oxygen, but the geometric complexity of the system has made it difficult to test the mechanism of oxygen supply. In a recent study, a team of researchers used two advanced imaging techniques (phase contrast microtomography and x-ray microscopy) to produce a three-dimensional mapping of the entire lantern (down to the smallest tracheole branches!) in two fireflies, Luciola terminalis and Luciola cerata.

Previous studies have shown that, in lanterns, mitochondria are clustered at the periphery of the photocytes (closer to the tracheoles, where gas exchange takes place). In normal conditions, oxygen that passes through the tracheoles is taken up by the mitochondria and doesn’t enter the peroxisomes where light is produced.

The researchers tested the hypothesis that mitochondrial activity is reduced to make part of the oxygen flux available for the bioluminescent reaction. They measured oxygen consumption for flashing and for mitochondrial functions, as well as the oxygen diffusion rate from tracheoles to the lantern tissue. They found that oxygen consumption for mitochondrial functions surpasses the maximum rate of oxygen diffusion from the tracheoles to the lantern cells.

In a nut (or should I say beetle?) shell, fireflies make energy-efficient flashes because they can divert oxygen away from the mitochondria in order to make light!

There are so many other aspects of bioluminescence in fireflies and other organisms that biologists are still researching. Perhaps you might be interested in looking more into the delightful world of bioluminescence, and sharing your findings with family, friends and other biology lovers! 

References:

Lewis, S. The Loves & Lies of Fireflies (Video). 2014. Accessed from web Jan. 27, 2015.

<http://www.ted.com/talks/sara_lewis_the_loves_and_lies_of_fireflies?language=en#t-421521 >

Timmins, G., et. al. Firefly flashing is controlled by gating oxygen to light-emitting cells. 2001. The Journal of Experimental Biology 204: 2795-2801.

Tsai, Y., et. al. Firefly light flashing: oxygen supply mechanism. 2014. Physical Review Letters 113: 258103.

Images:

Anglerfish: Finding Nemo monster is real: Rare black seadevil caught on video. 2014. Retrieved from web Jan. 27, 2015. <http://latestnewslink.com/2014/11/finding-nemo-monster-is-real-rare-black-seadevil-caught-on-video/>

Dancing fireflies: 30 Best Exposure Photography Pictures of the Week – May 22nd to May 29th, 2012. 2012. Retrieved from web Jan. 27, 2015. <http://beforeitsnews.com/awesome-time-wasters/2012/05/30-best-exposure-photography-pictures-of-the-week-may-22nd-to-may-29th-2012-2192381.html>

Firefly: Firely. 2015. Retrieved from web Jan. 27, 2015.  <http://www.firefly.org>

Luciferin Reaction: Science Buddies. 2015. Retrieved from web Jan. 27, 2015. <http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p033.shtml>

Mushrooms: Bioluminescent Mushrooms. 2014. Retrieved from web Jan. 27, 2015. <http://wasbella102.tumblr.com/post/63740128914/bioluminescent-mushrooms>

Plankton: Bioluminescent Plankton Glow In Bloom On The Shores Of Hong Kong. 2015. Retrieved from web Jan. 27, 2015.  <http://www.boredpanda.com/bioluminescence-hong-kong-noctiluca-scintillans-sea-sparkle/?image_id=bioluminescence-hong-kong-noctiluca-scintillans-sea-sparkle-3.jpg>

Tracheal system: Unraveling the light of fireflies. 2014. Retrieved from web Jan. 27, 2015. <http://phys.org/news/2014-12-unraveling-fireflies.html>