Bioluminescence, or the ability of a living thing to produce its own light, doesn't just exist to wow us on moonlight beaches or in biotechnology laboratories. It's an evolutionary mechanism, and depending on the species it lights up, it can help a critter avoid predators, lure in prey, or attract a mate. Scientists have historically believed bioluminescence appeared around 267 million years ago in ostracods, or "seed shrimp." But a new study of the marine subphylum Anthozoa reveals that bioluminescence has existed for over twice as long as previously thought. According to the researchers, certain corals kicked off nature's light show roughly 540 million years ago.
Because it's evolved independently across phyla about 100 times, the origin and progression of bioluminescence can be challenging to track. Researchers in the United States and Japan wanted to examine the history of bioluminescence within Octocorallia, a class of marine organisms under Anthozoa. While several of these "octocorals"—Isidella bamboo coral, the golden zoanthid, and others—have long been known to emit light, scientists know little about the feature's evolutionary origins or ecological roles within that class.
Using a database of 234 Anthozoans, the researchers mapped which species were bioluminescent, weren't bioluminescent, or had unknown or unconfirmed light production capabilities. Then, they further classified those species based on the marine depths at which they emitted light, if at all. The resulting graph gave them a starting point from which they could investigate how certain octocorals related to or differed from each other. Because every species in their database had been "fossil-calibrated," or dated according to their ancient remnants, the researchers could also trace when and with which species bioluminescence began within the Octocorallia class.
Certain orders, they found, didn't contain any confirmed bioluminescent species at all. Others, like sea anemone orders, involved just a few light-producing species. Within octocoral orders, however—Alcyonacea, Helioporacea, and Pennatulacea—an abundance of bioluminescent species appeared hundreds of millions of years ago. Using these species as "anchors" for their bioluminescence map, the researchers found that the ability to produce light had likely evolved just once within the Anthozoa subphylum and that it had first appeared in octocorals about 540 million years ago.
The team believes octocorals evolved to produce light in the Cambrian era, when creatures with eyes and other light-sensitive photoreceptors became prevalent. Bioluminescence would have been used to communicate with those marine species, such as in the case of spooking predators.
“I think our study really points to the fact that it’s one of the earliest forms of communication in the oceans—maybe one of the earliest forms of communication on Earth, really,” zoologist Andrea Quattrini told Scientific American. “It’s a fascinating form of communication that’s really quite simple at its core.”
