Nitric oxide and Firefly Flashing

 

A female Photuris sp. ready to devour a prey male. These femmes fatales use flash signals to lure in males of other species by imitating their females' flash patterns.

 

Firefly Links


Why do Fireflies Flash?

Fireflies rely on precise control of flash timing for two purposes: finding mates, and luring prey.

In the group Photinus, flashing represents a visible courtship signal. Within each species, males and females identify members of the opposite sex based on flash timing.

In the group Photuris, flashing serves an additional purpose. Female Photuris fireflies are highly specialized predators that can facultatively imitate the flash signal given by other species' females. Using this false signal, these predatory females are able to lure in unsuspecting Photinus males, then eat them (see the photo at the top of this page).

On the right are shown the flashes and flight paths of different species as they would appear in a time-lapse photograph (From: Lloyd, J. E. (1966). Univ. of Michigan Museum of Zoology, Misc. Pub. 130, 1-93)

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What is Nitric Oxide (NO)?

Nitric oxide (NO) is a soluble, highly reactive gas formed by natural chemical and physical reactions in the atmosphere. It is also produced by certain animal and plant cells from the amino acid, L-arginine. Because it is so small and diffusible NO passes through cell membranes and is often used as a biological signal.

In mammals NO helps to maintain blood pressure by dilating blood vessels, assists the immune system in killing invaders, and is a major factor in the control of penile erection (ViagraŽ works by blocking an enzyme in the NO/cGMP pathway). In the brain, NO plays a role in development, neuron to neuron signaling, and probably contributes to the formation of memories.

Most non-pathological functions of NO are mediated by activation of an enzyme, guanylyl cyclase, or by nitrosylation of proteins. However, NO can also inhibit oxygen consumption by mitochondria and it is this action that is exploited in producing firefly light flashes.

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What does a Firefly Lantern look like?

The Firefly lantern is located on the ventral abdominal surface (stippled area) beneath translucent cuticle. It is innervated by octopaminergic neurons in the posterior ganglia of the nerve cord. Bursts of action potentials in these neurons control the normal flash pattern. In each light-producing unit, photocytes are arranged radially into a rosette pattern around a central cylindrical core. The core includes a main air-containing trachea that originates dorsally and divides several times into fine tracheoles that project between the photocytes at several dorsal-ventral levels. Each trachea is ringed by tracheolar cells and tracheolar end cells. The luciferin-luciferase light producing reactions are confined to peroxisomes located centrally in photocytes. The photocyte mitochondria are found in the peripheral cytoplasm, concentrated especially at locations proximal to the trachea and tracheoles

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How is Firefly light produced?
Nitric oxide can activate Firefly light production
Luciferin is activated by luciferase in an ATP-dependent step to form a luciferin-adenylyl intermediate; when oxygen is present this intermediate is rapidly converted to a peroxyluciferin product that decays to oxyluciferin with the emission of photons.

When fireflies are placed into NO they begin to flash very rapidly and the lantern glows continuously. This response requires oxygen. Glowing is also evoked by applying the transmitter octopamine to the exposed lantern. Octopamine glow is inhibited by NO scavengers such as CPTIO.

The animation shown here is a slow-motion Photuris flash. Normal flashes and responses to NO can be seen in the movie link below (these are large files (80Mb), or at the Science website.

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View Quicktime movie of NO-induced bioluminescence

   


Where in the lantern is NO made?
How does it work?
Localization of nitric oxide synthase in the Photuris light organ. NADPH diaphorase activity (purple stain, a marker for NOS) is located at the center of each lantern rosette in the region around tracheal trunks. This region encompasses the tracheal cells, tracheal end cells, and the mitochondrial zone of the photocytes (see above). Similar staining is seen with an antibody to NOS. The white overlay (adapted from Case and Strause, in Bioluminescence in Action, Ed. Peter J. Herring, Academic Press NY 1978) shows the approximate location and dimensions of photocytes within a rosette.
Model for NO control of the firefly lantern flash. In quiescent mode (above dotted line), oxygen delivered through lantern tracheae is consumed by respiration in photocyte mitochondria (green) clustered in the peripheral cytoplasm: little oxygen reaches peroxisomes that contain the light-producing reactions of the luciferin-luciferase pathway. In this quiescent state, ATP produced by oxidative phosphorylation promotes formation and accumulation of the activated luciferin-adenylyl intermediate (denoted as luciferin*) by luciferase. In flash mode (below dotted line), nerve activity causes octopamine release that transiently activates lantern NOS. NO diffuses rapidly and inhibits oxygen use by photocyte mitochondria (red). Now oxygen delivered by the tracheal system diffuses through photocytes to the peroxisomes where it triggers the light-producing reaction.
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Author's Links

Barry Trimmer Ricardo Zayas and Sanjive Qazi Sara Lewis

June Aprille and Chris Lagace

Last Modified 6/28/2001 BAT