Shedding Light on Evolution: Octocorals Illuminate the Origins of Bioluminescence

Illuminating Discovery: Bioluminescence Evolved 300 Million Years Earlier Than Previously Thought

In a groundbreaking study published in the Proceedings of the Royal Society B, scientists from the Smithsonian National Museum of Natural History have revealed that bioluminescence, the ability of living organisms to produce light through chemical reactions, first evolved in marine invertebrates called octocorals around 540 million years ago. This discovery pushes back the origin of bioluminescence by nearly 300 million years from the previously accepted timeline.

The research team, led by museum research associate Danielle DeLeo, focused on octocorals, also known as soft corals, for three key reasons: their ancient history of bioluminescence, the availability of ample genetic data, and the team's extensive experience studying these organisms. By utilizing statistical modeling techniques and genetic data from 185 octocoral species, the researchers traced the probability of bioluminescence back through the octocoral evolutionary family tree.

While the team expected the trait to have ancient origins, the results surprised them. "We assumed the trait was going to be fairly ancient because it is an ancient group of animals and it's highly prevalent in the group," says DeLeo. The findings held true even after multiple tests were conducted to disprove the initial conclusion.

Despite this significant advancement in understanding the "when and how" of bioluminescence, the "why" remains a mystery. Scientists have associated bioluminescence with various behaviors, including camouflage, courtship, and communication, but these are merely theories at this point. "The current function in corals is a bit mysterious," admits DeLeo.

One theory suggests that the luminescent display might lure prey to the soft coral or serve as a warning to potential predators. "When you bump into the branches of these corals, they let off this bioluminescent light to possibly warn away potential predators," explains DeLeo. However, this function seems too sophisticated to have evolved so early in the history of life.

Another hypothesis proposes that bioluminescence initially evolved as a byproduct of a chemical process that protects cells from stress. As organisms became more complex over time, they retained this function because it proved advantageous in other ways.

The team's work not only sets a new starting point for investigating the divergence of bioluminescence but also opens up exciting avenues for future research. As scientists continue to unravel the mysteries surrounding the evolution and purpose of this captivating trait, we may gain a deeper understanding of the intricate relationships between organisms and their environments throughout Earth's history.