Scientists have pushed the earliest appearance of bioluminescence among animals back by nearly 300 million years.
Bioluminescence is when an organism produces its own light, through chemical reactions in the creature’s body. It occurs in some fungi, bacteria and insects such as fireflies. But it is particularly common among marine vertebrates and invertebrates.
Evidence suggests that bioluminescence evolved independently at least 94 times, but when did it first appear?
The oldest dated evidence of bioluminescence comes from fossils of ostracods – small marine crustaceans. The animals were alive about 267 million years ago, before the “Age of Dinosaurs.”
Looking at the evolutionary tree of a group of marine vertebrates called octocorals, however, a new study published in the Proceedings of the Royal Society B dramatically reassesses the earliest appearance of bioluminescence.
Octocorals includes soft corals, sea fans and sea pens. They are frequently bioluminescent, but usually only glow when disturbed. The purpose of this luminescence is unclear.
“We wanted to figure out the timing of the origin of bioluminescence, and octocorals are one of the oldest groups of animals on the planet known to bioluminesce,” says lead author Daniel DeLeo, from the Smithsonian’s National Museum of Natural History. “So, the question was when did they develop this ability?”
They made an evolutionary map, or phylogeny, using genetic data from 185 species of octocorals.
“If we know these species of octocorals living today are bioluminescent, we can use statistics to infer whether their ancestors were highly probable to be bioluminescent or not,” explains senior author Andrea Quattrini, the museum’s curator of corals. “The more living species with the shared trait, the higher the probability that as you move back in time that those ancestors likely had that trait as well.”
Different statistical methods all arrived at the same result: bioluminescence appears to have evolved in octocorals 540 million years ago.
“Nobody quite knows why it first evolved in animals,” Quattrini says. Finding out why will be at the heart of future research by the team.
By looking at which of the 3,000 species of octocoral light up compared to those which don’t, the scientists believe they may be able to pinpoint the ecological circumstances which led to the evolution of bioluminescence.
