Glow-in-the-dark Ocean Fish Are More Widespread Than Known


In the darkest depths of the ocean, several marine species light up like bright stars in the night sky.

It's all thanks to bioluminescence or the production of light from a living creature. Bioluminescence is a biological phenomenon more recognizable in fireflies and terrestrial fungi.

Now, in a new report published in the journal PLOS ONE, scientists reveal that the phenomenon is actually widespread among deep-sea fish than originally known. Indeed, the ability to produce light may have progressed at least 27 times among these marine creatures, the report says.

Under The Sea

Past studies have shown that bioluminescence, which allows living organisms to create light through a myriad of chemical reactions, had evolved just 40 times in the Tree of Life from a handful of common ancestors.

However, scientists now say this appears like an underestimation. In fact, according to a new analysis of the marine tree of life, the "lights" under the sea did not originate from only a few creatures.

How did experts figure this out?

Led by Matthew Davis of St. Cloud State University, a team of researchers analyzed nuclear and mitochondrial gene fragments taken from more than 300 taxa or taxonomic groups.

This helped researchers infer the number of independent evolutionary origins of bioluminescence, as well as investigate the diversification in these lineages.

Davis and his team focused on ray-finned fish fish that were trawled up from the depths, given that existing cameras cannot adequately capture bioluminescence deep into the ocean.

Scientists discovered that the ability to produce light evolved independently 27 times in 14 major fish clades or groups of fish with a common ancestor.

This finding suggests that all fish included in the research have been developing bioluminescence ever since the Early Cretaceous period, which was about 150 million years ago.

Additionally, Davis and his colleagues suggest that in several cases, but not all, once a clade of fish developed bioluminescence, it thereafter sprang into many new marine species.

Limitations Of The Study

Because scientists only managed to study the marine creatures glowing in the lab, study author John Sparks says the phenomenon deep in the sea may not be the same in experiments.

Many of the fish will glow in the lab, but although their heads possess intricate arrangements of organs that produce light, the fish will only turn these organs on all at once.

Sparks says this may not be the fish's natural behavior because he believes the fish use bioluminescence to create complex signals under the deep ocean.

Sparks hopes to further study creatures in their natural habitat someday in order to understand why the light-producing phenomenon evolved countless times.

Possible Function

Indeed, the creatures that tended to use bioluminescence for something complex enjoyed the most biodiversity, Sparks says. He says there are no barriers to keep species from reproducing with other species.

This suggests that bioluminescence may have helped boost the diversity of these deep sea creatures. The number of creatures in the marine family tree appeared to increase after the evolution of the light-producing phenomenon, researchers say.

In the meantime, Sparks, Davis and the rest of the team hope to finish developing a deep-sea camera that would help them capture flash signals deep into the ocean.

"Right now, we have no idea how they flash. When something evolves so many times, you know it's obviously very important," adds Sparks.

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