The Evolution of Illumination

Research Blogging / by Dave Munger /

Researchers are now uncovering how—and why—bioluminescent organisms evolved the ability to glow.

One of the most alluring visual feasts in the movie Avatar was its alien biosphere of glowing plants and animals. Nearly every living thing on the moon Pandora seemed to shimmer and sparkle—sometimes in response to touch, other times as an expression of emotion. It’s something that separates this magical world of make-believe from the real world here on Earth.

Or is it? While bioluminescent organisms are perhaps not as common in the real world as they are in science fiction, they do exist, in a surprising variety of places. I first encountered them at night on a dock near my childhood home in Seattle. Initially the waters of Puget Sound seemed dark, but dipping a hand revealed a luminous surprise—tiny glowing bits appeared, like underwater sparks, wherever my hand disturbed the water. Then I saw a glowing fish swim by, leaving a luminous trail. The fish wasn’t actually glowing; rather, it was causing tiny bioluminescent dinoflagellates to glow as it passed them. This may be a defense mechanism for the dinoflagellates. Since any movement by their predators causes them to glow, this light may attract other, larger predators that could then do away with the danger.

Image courtesy of Jeremy Marr

Christie Lynn, a graduate student in cell and molecular biology at the University of Hawaii, points out that dinoflagellates aren’t the only creatures in the sea that glow. Indeed, at depths of greater than 1,000 meters, where no light from the surface can reach, it has been estimated that nearly 90 percent of creatures emit some kind of light. These aren’t just microorganisms: Fish, squid, jellyfish, and shrimp are also commonly bioluminescent at these depths.

Their lights have a variety of purposes: Camouflage, attracting mates, attracting (or distracting) prey have all been observed. In animals with nervous systems, in most cases, neural activity initiates the bioluminescence. But in the velvet belly lantern shark, Lynn says, researchers found that the glowing was not caused by nerve cells. Instead, it seemed, certain hormones controlled the glow: Melatonin and prolactin turned it on, and a hormone called Alpha-MSH turned it off. This makes some sense, as melatonin is activated by darkness (it helps control sleeping behavior in humans). This species of shark uses glowing as a form of camouflage. It swims around 500 meters below the surface, and its glowing belly, matched to the dim light filtering down from above, make it less visible from below.

Bioluminescence isn’t limited to the deep, dark portions of the ocean. Lucas Brouwers is a graduate student in Molecular Mechanisms of Disease in Nijmegen, the Netherlands. He blogs about a coral that is ordinarily a dull shade of brown, but glows in a vivid rainbow of colors under certain conditions. The coral’s glow is due to the dinoflagellates living inside it in a symbiotic relationship. Bioluminescence is most commonly a yellow-green color, whether in fireflies or phytoplankton, so naturally researchers have been interested in how the wide array of colors exhibited by these corals evolved.

Using a very clever technique, Steven F. Field and Mikhail V. Matz of the University of Texas at Austin reconstructed the evolution of the proteins responsible for the coral dinoflagellates’ luminescence—all on a petri dish. Their results were published last September in the Journal of Molecular Biology and Evolution. Field and Matz examined all the different possible mutations of the bacterial genome between a green ancestor and modern red-glowing bacteria, using 20,000 different cell cultures. Through a process of elimination, they identified 20 critical mutations in the genome that were responsible for the variety of colors we see today. Interestingly, these mutations are epistatic: That is, individually, they don’t result in much difference, but combined, they result in the vibrant, bold colors of the coral’s glow, ranging from blue to red. The researchers were even able to illustrate these genetic relationships by using colonies of the host bacteria to construct a living phylogenetic tree.

Of course, the creature many of us associate with bioluminescence doesn’t live in the oceans at all. Zen Faulkes, a biologist at the University of Texas–Pan-American, uncovered a study about the glowing “firefly,” actually one of several glowing beetles. When I first saw fireflies after I moved to the southern US, I wondered how that glow could possibly be beneficial. Wouldn’t it attract predators? A team led by Paul R. Moosman studied how insect-eating bats respond to the glowing fireflies. They found relatively few remnants of fireflies in bat droppings, and caged bats rejected pieces of fireflies as food. Perhaps the glow of a firefly serves as a signal to potential predators that they are distasteful or poisonous, just like red berries signal danger to herbivores. Indeed, the researchers did find that some bats attacked glowing lures less than non-glowing lures, although Faulkes says the results weren’t conclusive for all bat species that were studied.

So while it’s possible that one purpose of the glow of fireflies is as a warning for predators, clearly much remains to be learned about the function of bioluminescence. As more research is done, look for commentary and analysis on ResearchBlogging.org.

Originally published February 17, 2010

Tags competition research

Share this Stumbleupon Reddit Email + More

Now on SEEDMAGAZINE.COM

  • Ideas

    I Tried Almost Everything Else

    John Rinn, snowboarder, skateboarder, and “genomic origamist,” on why we should dumpster-dive in our genomes and the inspiration of a middle-distance runner.

  • Ideas

    Going, Going, Gone

    The second most common element in the universe is increasingly rare on Earth—except, for now, in America.

  • Ideas

    Earth-like Planets Aren’t Rare

    Renowned planetary scientist James Kasting on the odds of finding another Earth-like planet and the power of science fiction.

The Seed Salon

Video: conversations with leading scientists and thinkers on fundamental issues and ideas at the edge of science and culture.

Are We Beyond the Two Cultures?

Video: Seed revisits the questions C.P. Snow raised about science and the humanities 50 years by asking six great thinkers, Where are we now?

Saved by Science

Audio slideshow: Justine Cooper's large-format photographs of the collections behind the walls of the American Museum of Natural History.

The Universe in 2009

In 2009, we are celebrating curiosity and creativity with a dynamic look at the very best ideas that give us reason for optimism.

Revolutionary Minds
The Interpreters

In this installment of Revolutionary Minds, five people who use the new tools of science to educate, illuminate, and engage.

The Seed Design Series

Leading scientists, designers, and architects on ideas like the personal genome, brain visualization, generative architecture, and collective design.

The Seed State of Science

Seed examines the radical changes within science itself by assessing the evolving role of scientists and the shifting dimensions of scientific practice.

A Place for Science

On the trail of the haunts, homes, and posts of knowledge, from the laboratory to the field.

Portfolio

Witness the science. Stunning photographic portfolios from the pages of Seed magazine.

SEEDMAGAZINE.COM by Seed Media Group. ©2005-2015 Seed Media Group LLC. All Rights Reserved.

Sites by Seed Media Group: Seed Media Group | ScienceBlogs | Research Blogging | SEEDMAGAZINE.COM