Glowing Octocorals Have Existed For at least 540 Million Years

Recent genetic and fossil studies suggest that over half a billion years ago, ancient oceans sparkled with the luminous glow of bioluminescent corals. These findings, published on April 24 in the Proceedings of the Royal Society B, suggest that bioluminescence originated nearly 300 million years earlier than previously believed.

Danielle DeLeo, an integrative biologist at the National Museum of Natural History in Washington, D.C., led the study. “This research marks the earliest evidence of bioluminescence on our planet, significantly extending the timeline previously established by a 2022 study,” DeLeo stated. The 2022 study identified bioluminescence in a 267-million-year-old precursor to today’s sea fireflies, tiny crustaceans resembling seeds.

Bioluminescence, the ability to emit light through chemical reactions, has evolved independently around 100 times among various life forms, including fish, corals, and fungi. This trait can assist in hunting, mating, and evasion from predators.

DeLeo’s team focused on a particular subgroup of corals known as octocorals, which include species like soft corals, sea pens, and sea fans. Many of these species inhabit deep oceanic environments and exhibit an 8-fold symmetry, with several displaying bioluminescence.

By analyzing DNA from 185 octocoral species, the researchers identified genetic patterns that allowed them to construct an evolutionary tree. They also utilized octocoral fossils to pinpoint when specific lineages diverged. Their calculations suggest a high likelihood that the ancestors of these corals were bioluminescent, dating back to about 540 million years ago.

“This ancient lineage of bioluminescent octocorals underscores the trait’s volatile nature in evolutionary terms; it appears and disappears relatively easily,” remarked Todd Oakley, an evolutionary biologist from the University of California, Santa Barbara, who was not involved in this study but led the 2022 research on sea fireflies.

Jessica Goodheart, an evolutionary biologist at the American Museum of Natural History in New York City, is keen to explore how bioluminescence may have influenced the diversification of the octocoral group.

DeLeo suggests that bioluminescence may have initially emerged as a secondary effect of older cellular chemical processes, which were then adapted for signalling and communication, providing a survival benefit.

The research also raises the possibility that other ancient organisms, such as bacteria, algae, and comb jellies, might have developed bioluminescence even earlier than octocorals. However, limitations in the fossil record make it difficult to determine the exact origins of this trait.

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