In the darkest corners of the planet, where the light of the Sun never touches, eerie glows can yet be found, illuminating the shadows.
This is bioluminescence, a remarkable ability that has evolved, separately, at least 94 times throughout the history of life on Earth.
Bioluminescent organisms can harness chemical reactions to produce a glow of their own, a tool used for various purposes by the different creatures that wield it.
Now, scientists have traced this tool to its earliest known evolutionary origins: a class of corals called Octocorallia in the depths of the ocean in the Cambrian, some 540 million years ago.
This is more than double the age of the previous title holder, a tiny deep-ocean crustacean that lived 267 million years ago.
The team deployed several different statistical analyses, and they all returned a similar result: bioluminescence first emerged in the common ancestor of all octocorals some 540 million years ago.
The emergence of bioluminescence at the same time suggests an inter-species interaction of some kind, and could help figure out why the ability evolved.
If the common ancestor of the thousands of octocoral species alive today had bioluminescence, why do so few have it now?
Unsettling glows that illuminate the shadows can still be found in the planet’s darkest regions, where the Sun never shines.
This is bioluminescence, an amazing ability that has independently evolved at least 94 times in the history of life on Earth. The ability of bioluminescent organisms to control chemical reactions to produce their own glow is a tool that these diverse creatures use for a variety of objectives.
As of late, researchers have linked this instrument to its earliest known evolutionary ancestors, a class of corals known as Octocorallia that lived 540 million years ago in the Cambrian ocean’s depths. The tiny deep-ocean crustacean that held the title before it died 267 million years ago is more than twice as old as this one.
Marine biologist and lead author Danielle DeLeo of the Smithsonian Institution and Florida International University says, “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.”.
“So, when did they acquire this ability?” was the query.
The octocorals are an amazing group of animals. They are composed of polyps, just like other corals, which group together to form colonies and frequently reside on framework composed of their calcified secretions. On the other hand, octocorals—named for the eight-fold symmetry of the polyps—have softer skeletons than their more inflexible kin.
It is also known that some of them exhibit bioluminescence, though the cause of this is unclear because it only happens when they are disturbed. Researchers speculate that it may serve as a lure for larger fish that eat coral or as a catch for predators.
allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-sharing” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>. frameborder=”0″.
DeLeo and her colleagues believed that corals, which are among the planet’s oldest organisms, and octocorals, which are known to glow, might be the best places to search for the earliest examples of bioluminescence. Additionally, the foundation was already established; in 2022, a comprehensive family tree comprising 185 octocoral taxa was published through genetic data analysis.
Next, marine biologists Manabu Bessho-Uehara of Nagoya University in Japan and Andrea Quattrini of the Smithsonian Institution identified and traced the lineages of known species of bioluminescent octocorals that had been collecting as part of fieldwork.
Their explorations of the seafloor revealed hitherto undiscovered bioluminescence in five different species of octocoral; this finding could be useful for their upcoming analysis, known as ancestral state reconstruction.
According to Quattrini, “if we know these species of octocorals that are alive today are bioluminescent, we can use statistics to infer whether or not their ancestors were highly probable to be bioluminescent.”.
“The greater the number of extant species sharing a particular trait, the more probable it is that those ancestors also shared that trait at some point in the past. “.
The group used a variety of statistical techniques, and each produced a similar conclusion: 540 million years ago is when bioluminescence first appeared in the common ancestor of all octocorals. Although multicellular life was still in its infancy at this time, the Cambrian ocean was home to marine invertebrates that possessed eyes that could detect light.
Simultaneous emergence of bioluminescence points to the possibility of some sort of interspecies interaction, which may help explain why the ability evolved.
However, there is still a very important question. Next steps could provide more insight into the peculiar ecology of the Cambrian ocean, such as explaining why so few of the thousands of species of living octocorals today have bioluminescence and how they lost it.
