In 2017, two evolutionary biologists snorkeling off the coast of Panama made a surprising discovery.
Night was falling on the shallow waters of Bocas del Toro and Giacomo Morinprofessor emeritus of Cornell University, turned on his underwater flashlight to glimpse the seabed.
Seemingly in response, hundreds of tiny blue lights came to life, rippling in waves.
“We were both swearing into our snorkels in amazement,” he said Todd Oakleyprofessor at the University of California, Santa Barbara.
In a document published In Proceedings of the Royal Society B on Wednesday, scientists detailed the courtship rituals of a new species of “sea firefly” — a tiny crustacean no bigger than a grain of sand that puts on a spectacular underwater show by sneezing bright mucus.
But these are not simple flashes. Like the synchronous performances of groups of fireflies on land, the sea firefly light show is a carefully choreographed dance in harmony with the rhythms of the night sky.
“It’s an underwater fireworks display — the best Fourth of July you’ll ever see,” he said Nicholas Hensleya postdoctoral researcher at Cornell who studies animal behavior and conducted the new study.
The creatures behind the Panamanian light show are called ostracods. Dr. Hensley compares the tiny crustaceans to sesame seeds with eyeballs. Under the microscope you can make out the shrimp-like body of an ostracod, encased in a transparent shell.
A bizarre organ called the “upper lip” produces many bioluminescent ostracods. The upper lip stores two chemicals that, when combined, create a bright blue explosion.
“It’s literally like a handlebar whisker of shining light right above the mouth,” Dr. Hensley said.
Ostracods around the world use their glowing snot for many purposes, such as putting on courtship displays or forcing predators to spit them out (apparently mucus tastes really bad). But Dr. Morin said the sea fireflies’ light show was “on steroids” the night he and Dr. Oakley observed them, and they coordinated in a way that other species fail to do.
The team studied this mysterious population of sea fireflies, which bore the temporary name “EGD” (for “training lawn feller”), and persuaded them to repeat the light show in captivity. Now, researchers believe they have pieced together the individual steps of EGD’s courtship dance.
The love story begins at nautical twilight, an in-between time when the sun has set, the moon has yet to rise, and the sea fireflies’ only competition for brightness is starlight. Each male rises from the flowerbeds and then descends in a tight, spiraling dive, sneezing between four and eight orbs of light as he goes. The result is stunning, scientists agree, like a string of Christmas lights or a string of luminous pearls.
EGD males are highly suggestible, the team found. The first male to produce glowing snot sets off a chain reaction as his neighbors follow suit, causing ripples of light. And the further a sea firefly is from its nearest rival, the more snot pearls it produces, perhaps because it has a better chance of courting females if its competitors are out of reach.
Although bioluminescence is common in the ocean, this type of coordinated, group display is impressive for a creature the size of a sesame seed, he said Edith Widderbioluminescence expert and CEO of the Ocean Research and Conservation Association, who was not involved in the study.
Dr. Widder praised Dr. Hensley’s study for providing “rare” information about bioluminescent courtship, which generally occurs beyond the reach of scientists. He said the phenomenon is a striking example of convergent evolution since both aquatic and terrestrial fireflies separately developed similar manifestations, although the last common ancestor of the two creatures lived about 500 million years ago.
In some ways, Dr Widder added, the EGDs’ light show is even more ingenious than that of their winged cousins: the firefly must reveal its position when its light flashes, but the sea firefly can put distance between itself and its light erupted. . It’s like a bright, coded map: Females of the species know how to “read” the display to find their arrogant suitors, while predators are left in their tracks.
Dr. Hensley said he can’t help but marvel at how this incredible dance took place, unnoticed, yet so close to civilization. In the seagrass beds of Bocas del Toro where the species was discovered, as ostracods form their underwater constellations in hopes of finding love, you can hear the thumping bass of the disco right on the beach.