It is nearly one month past the summer solstice and here in southern Wisconsin, the glow of fireflies at dusk and into darkness is a summertime pleasure not to be missed.

Fireflies employ the substrate luciferin and the enzyme luciferase, to produce their bioluminescence. The flash of a firefly lantern is designed to attract a mate, although with some species the potential mate becomes prey. Different species of fireflies have different flash patterns, which helps them find one of their own, when pairing off to create new little shiners.

In contrast to showy bioluminescence during night time flight, ocean depths have luminescence displays from a wide variety of creatures. Many of these bioluminescent sea creatures are recent discoveries, their discovery, habitat and behavior identified with the use of mini-submarines and non-manned submersibles.

One glowing example is the cluster wink snail. Terrestrial snails have been noted to leave a slightly luminescent trail of snail mucus as they crawl. But in 2010, the cluster wink snail was noted to flash a bright green light throughout  its entire shell. What better than an illuminated shell?

The snail has been noted to light up when disturbed, perhaps because the light makes the snail look larger. Or the bright flash may attract larger predators to come closer, scaring away the initial interrogator.

The Abraliopsis squid has luminescent display organs composed of photophores on its underside for protection. These light displays allow the squid to disappear against a backlit sky when predators are swimming below it.

The Botrynema is a deep water jellyfish found off the coasts of Antarctica and Alaska. Little is know about the creature, but it’s luminescence is multi-colored and astounding.

A 2009 Journal of Experimental Biology article, reported the first luminescence to be controlled by hormones in a luminescent shark. Researchers examined pieces of lantern shark skin exposed to prolactin, melatonin and alpha-melanocyte-stimulating hormone (α-MSH), and demonstrated that the skin luminesced with exposure to melatonin and prolactin, while α-MSH shut down the luminescence.

More commonly in bioluminescence, the stimulating event is triggered via nerve cells. Another difference is that the shark glow starts more slowly; rather than a flash of light, this glow slowly appears and intensifies, lasting over a period of hours.

This new mechanism upped the ante for bioluminescence by demonstrating two parallel  evolutionary tracks. Bioluminescence evolved in certain marine and terrestrial creatures via signaling by nerve cells (in fireflies, jellies and other bony fish) while the lantern shark luminescence occurs via hormonal stimulation.

As in the case of several other deep sea luminescent animals, lantern shark luminescence is thought to protect the shark from predators below it, as luminescence helps conceal the shark against the backlighting of the lighter surface above.

If your summer travel plans bring you close to any bioluminescent creatures, whether on land, in the air or in the ocean depths, we would love to hear about it.

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Kari Kenefick

Kari has been a science writer/editor for Promega since 1996. Prior to that she enjoyed working in veterinary microbiology/immunology, and has an M.S. in Bacteriology, U of WI-Madison. Favorite topics include infectious disease, inflammation, aging, exercise, nutrition and personality traits. When not writing, she enjoys training her dogs in agility and obedience. About the practice of writing, as we say for cell-based assays, "add-mix-measure".

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