Why Bioluminescence?

Heating a house with a wood stove does involve some tedium and even inconvenience. One is adding wood to the stove in the wee hours. A while back, at maybe four or so in the morning, I went down to stoke the stove. The wood at hand had loose bark which I always remove if possible. I removed the bark and to my surprise in the dark house, the bark glowed a pale green.

This is a good example of bioluminescence, a way of producing light without heat. It occurs across the living world – plants, animals, fungi, and bacteria. Light is produced when certain molecules (substrates) react with oxygen with a special catalyst. This releases energy but unlike all other energy-producing reactions, allows the energy to be released in the form of light. The different molecular substrates produce different colors.

In the deep ocean where most bioluminescent organisms live, the predominant color is blue as that is the color that is least absorbed by water. Other colors occur but are much less common. Some organisms don’t produce light themselves but rather keep bioluminescent bacteria in special organs. In the pitch-black darkness of the deep ocean, bioluminescence is used for all sorts of signaling.

Some toxic worms signal their status to avoid predators, other organisms avoid predation by flashing so brightly and colorfully as to dazzle predators. Some will actually lose a glowing appendage to distract. On the other hand, some predators use a bright flash to dazzle prey. Some predators can use their luminescence to act as a flashlight in the dark, illuminating prey.

There are luminescent organisms even at the surface of the oceans. Certain flagellates luminesce, turning the surface of the ocean into a pale green field, often sparkling when disturbed. And then there is sexual signaling.

There are thousands of species of fireflies and most of them are luminescent. Almost all these species use the light to signal species identification for sexual signaling. Often the flash rate or pattern of flashing is unique to a single species. This allows conspecifics to connect for mating.

A really unique firefly species is a sort of black widow or maybe femme fatale. The females of this species mimic the “flash code” of other species of fireflies. When the males of another species are attracted to the false signal, they are promptly eaten. They don’t even get that last hurrah as do the males of some spiders who at least get to have sex before they get their heads bitten off.

Even the fungi may have sex in mind. The wood rot fungus which glows faintly green, the one I observed, is thought to use the glow to attract insects which are useful for spore dispersal – OK not exactly sex, but propagation.

The value of light production is sufficiently important to have arisen evolutionarily over thirty times over hundreds of millions of years.

Dr. Bob Allen is Emeritus Professor of Chemistry, Arkansas Tech University. His website is Bob of the Ozarks, www.ozarker.org

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