Bioluminescence evolved in the abyss 540 million years ago, research shows

In the darkest corners of the planet, where the sun’s light never touches, eerie glows can still be found illuminating the shadows.

This is bioluminescence, a remarkable ability that has individually evolved at least 94 times in the history of life on Earth. Bioluminescent organisms can harness chemical reactions to produce a glow of their own, a tool used for a variety of purposes by the different creatures that interact with them.

Now scientists have traced this tool back to its earliest known evolutionary origins: a class of corals called Octocorallia in the depths of the ocean in the Cambrian period, some 540 million years ago. This is more than double the age of the previous title holder, a small deep-sea crustacean that lived 267 million years ago.

“We wanted to determine the timing of the origin of bioluminescence, and octocorals are one of the oldest groups of animals on Earth known to produce bioluminescence,” said marine biologist and lead author Danielle DeLeo of the Smithsonian Institution and Florida International University.

“So the question was when did they develop this ability?”

Octocorals are a fascinating group of creatures. Like other corals, they consist of polyps that together form a colony, often living on a framework made from their calcified secretions. However, octocorals, which get their name from the eightfold symmetry of the polyps, have softer skeletons than their stiff relatives.

Some of them are also known to exhibit bioluminescence, but the reason for this is a bit of a mystery as they only do this when disturbed. Scientists think it could be an attractant for prey, or for predators to come and eat the smaller fish that feed on and damage the coral.

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Because corals are among the oldest organisms in the world, and octocorals are known to glow, DeLeo and her colleagues thought these organisms might be the best place to look for the early origins of bioluminescence. And the groundwork had already been laid, with a detailed family tree of the octocorals published in 2022, using genetic data from 185 octocoral taxa.

The next step was to identify and trace the lineages of known species of bioluminescent octocorals, collected as part of fieldwork conducted by marine biologists Manabu Bessho-Uehara of Nagoya University in Japan and Andrea Quattrini of the Smithsonian Institution.

Their forays into the seafloor identified previously unknown bioluminescence in five octocoral types – a discovery they could use for the next step, an analysis called ancestral state reconstruction.

“If we know that these species of octocorals alive today are bioluminescent, we can use statistics to infer whether it was very likely that their ancestors were bioluminescent or not,” Quattrini explains.

“The more living species with the shared trait, the greater the chance that if you go back in time, those ancestors probably also had that trait.”

The team ran several statistical analyses, all of which yielded a similar result: bioluminescence first emerged about 540 million years ago in the common ancestor of all octocorals. At that time, multicellular life was still in its infancy, but there were marine invertebrates with eyes that could detect light that shared the Cambrian ocean.

At the same time, the emergence of bioluminescence suggests some kind of interaction between species, and could help uncover why this ability evolved.

But a big question remains. If the common ancestor of the thousands of octocoral species alive today had bioluminescence, why do so few have it now? And how did they lose it? That’s the next step and could shed more light on the strange ecology of the Cambrian Ocean.

The research was published in Proceedings of the Royal Society B Biological Sciences.