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Science
Study Reports on Chemical Turn-ons for Fireflies
The summer sun sets and twilight descends, thousands of flashing, flying beetles
take to the air. Their glowing, lantern-like abdomens annually send children
racing, jar in hand, as if summer itself could be held captive on a windowsill.
Poets have been similarly enchanted by fireflies-known to those living south
of the Mason-Dixon line as “lightning bugs.”
Scientists have understood for some time that male fireflies flash to attract
females, who wait in nearby trees or bushes. For very young fireflies, glowing
abdomens may also be useful for warding off predators, as an “aposematic”
display. And, researchers long ago explained how chemical energy is converted
into a bioluminescent glow.
But, how does the firefly know exactly when to start flashing?
Like a chemical conductor’s baton, our nightly light-show gets the green
light from nitric oxide (NO), a new Science study shows. A biochemical
messenger that controls blood flow and mediates learning and memory in humans,
nitric oxide is perhaps best known for its role in treating erectile dysfunction.
“We knew about the chemistry that makes fireflies light up,” said
Barry Trimmer of Tufts University, lead author of the study. “Now, we have
the missing piece of the puzzle that explains how they are able to throw the
switch on and off.”
Many animals, including jellyfish and bacteria, are capable of the seemingly
magical feat of bioluminescence. But, said co-author Sara Lewis of Tufts, “The
firefly’s talent for producing precisely timed, rapid bursts of light is
quite rare.” This ability has allowed fireflies to develop an elaborate
courtship based on flash communication.
“Fireflies are very romantic beasts,” Lewis said, “because their
whole adult life is spent courting.” Fireflies encompass thousands of different
species, each with its own unique flash-code form of identification. Male and
female flash patterns differ, but both sexes use a light-producing abdominal
lantern.
“How do they do that?” is a question asked by firefly watchers of
all ages.
The Science study shows that, jump-started by an influx of oxygen, a chemical
reaction within cells in the firefly lantern produces the insect’s flow.
Experiments suggested that nitric oxide transmits the neural message to “start
flashing” from cells at the ends of branching air tubes in the firefly
lantern, to mitochondria that surround the lantern’s light-producing organs.
The researchers propose that nitric oxide inhibits mitochondrial oxygen respiration,
which in turn raises the levels of oxygen available to the light-producing cells,
turning on the flash.
These findings help explain how the flash-control machinery works, and how
it is triggered by nitric oxide, described by co-author Thomas Michel of Brigham
and Women’s Hospital as “the smallest molecule known to carry messages
between cells.”
Such technical insight may be lost on toddlers reaching for glowing beetles
this summer. But, the research contributes significantly to our understanding
of the world around us.
-- Becky Ham
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Public & Press Center
