Bioluminescence may have evolved 300 million years earlier than scientists previously thought

Many marine organisms, including sea worms, some jellyfish, sea pickles and more, can emit an ethereal glow through a process called bioluminescence. The evolutionary origins of this light production remains a mysteryBut an international team of scientists has discovered that bioluminescence may have first evolved in a group of marine invertebrates called octocorals at least 540 million years ago – almost 300 million years earlier than they previously thought. This new timeline could help scientists unravel the origin story of bioluminescence. The findings are detailed in a study published April 23 in the journal Trial of the Royal Society B.

What is bioluminescence?

Bioluminescent organisms produce light through chemical reactions. This ability evolved independently at least 94 times in nature. Bioluminescence is involved in multiple animal behaviors, including communication, courtship, camouflage and hunting. Fireflies, glowworms and even some types of fungi on land are also considered bioluminescent organisms.

“Nobody knows exactly why it first evolved in animals,” said Andrea Quattrini, co-author of the study and curator of corals at the Smithsonian Museum of Natural History, said in a statement.

This was believed to be the earliest dated example of bioluminescence in animals about 267 million years ago in small marine crustaceans known for their mucus-filled, synchronized mating dance, called ostracods, until this new research turned back the clock.

An octocoral evolutionary tree

In the studythe team looked back into the evolutionary history of octocorals for clues as to when it first appeared in animals. Octocorals are an ancient and often bioluminescent group of living animals, including sea fans, sea pens and soft corals. Like hard corals, octocorals are small colonial polyps that build a reef structure, but they are mainly soft and not stony. The octocorals that glow generally light up when bumped or otherwise disturbed. According to the teamThis makes the precise function of their ability to produce light a bit of a puzzle

[Related: These newly discovered bioluminescent sea worms are named after Japanese folklore.]

“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,” study co-author and postdoctoral researcher Danielle DeLeo of the Smithsonian National Museum of Natural History. said in a statement. “So the question was when did they develop this ability?”

They turned to a detail evolutionary tree of octocorals built in 2022. This map of evolutionary relationships – or phylogeny–uses the genetic data of 185 different species of octocorals. The team then placed two octocoral fossils of known ages in the tree based on their physical characteristics. They were able to use the ages of the fossils and their respective positions in the evolutionary tree to roughly determine when octocoral lineages split to become two or more branches. The team ultimately mapped out the evolutionary relationships encompassing all known bioluminescent species alive today.

With this evolutionary tree and branches containing bioluminescent species labeled, the team used a statistical technique called reconstruction of the ancestral state to analyze the relationships between the species.

“If we know that these species of octocorals alive today are bioluminescent, we can use statistics to infer whether it was highly likely that their ancestors were bioluminescent or not,” says Quattrini. “The more species that live with a common characteristic, the greater the chance that if you go back in time, those ancestors probably also had that characteristic.”

Multiple different statistical methods all achieved the same result. About 540 million years ago, the common ancestor of all octocorals was most likely bioluminescent. This is about 273 million years earlier than the ostracod crustaceans previously considered the earliest evolutionary example of bioluminescence in animals.

According to the teamThe octocorals’ thousands of living species and relatively high incidence of bioluminescence suggest that glowing played a role in the group’s evolutionary success. While this doesn’t answer exactly what octocorals use bioluminescence for, the fact that it has been on the market for so long shows how important this form of communication has become to their survival.

Implications for conservation

Now that the team knows that the common ancestor of all octocorals could likely already produce its own inner glow, they are interested in a more thorough count of which of the octocorals group has more than 3,000 known living species are still bioluminescent and have lost this property over time. This allows them to identify a range of ecological conditions that correlate with bioluminescence and potentially shed some light on its function.

The team is also busy making a genetic test to determine whether an octocoral species has functional copies of the genes Luciferase–an enzyme involved in bioluminescence. Future studies could even show that bioluminescence is even older and embedded in coral’s evolutionary history.

[Related: Surprise! These sea cucumbers glow.]

The study also points to evolutionary insights that could help monitor and manage octocorals in today’s oceans. They are currently threatened by mining, fishing, oil and gas extraction and spills, and human-induced climate change.

The National Oceanic and Atmospheric Administration (NOAA) recently confirmed that the planet is currently experiencing the fourth global coral bleaching event on record and the second in the past decade due to heat stress from increasingly warm oceans. Octocorals can bleach like hard corals can do under extreme temperatures. Understanding more about how they use bioluminescence will help scientists better identify their habitats and monitor their behavior. Better knowledge of their genetics and what they need to survive can also contribute to better conservation policies for these marine organisms.