In the deep sea, far from the sun’s reach, a mysterious light still occasionally pierces the perpetual gloom. This phenomenon, known as bioluminescence, is a unique adaptation that has evolved in numerous species across the tree of life, independently 94 different times. Creatures harness this bioluminescent capability for varied reasons, creating their own glow through special chemical reactions.
Researchers have now pinpointed the most ancient origins of this trait to a group of corals known as Octocorallia, which resided in the ocean’s abyssal zones during the Cambrian period approximately 540 million years ago. This discovery pushes back the first occurrence of bioluminescence more than twice as far into the past compared to a much younger species, a deep-sea crustacean that lived 267 million years ago and previously held the record.
“We were curious about when bioluminescence first appeared, and since octocorals are among the earliest animals with this feature, they provided a good starting point for our investigation,” stated Danielle DeLeo, a marine biologist and the study’s leading author, from the Smithsonian Institution and Florida International University.
“We sought to uncover the exact timing of the evolution of this trait in them,” she added.
Octocorals are intriguing — forming colonies of polyps that support themselves with flexible, calcified secretions differing from the stiffer skeletons of other corals. Known for bioluminescent discharges when disturbed, scientists hypothesize that this reaction could serve as either a defense mechanism or as a way to attract prey or larger predators who might then target the smaller fish that harm the coral.
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Leveraging a detailed octocoral family tree from 2022 and recent fieldwork discoveries by Manabu Bessho-Uehara of Nagoya University and Andrea Quattrini of the Smithsonian Institution, which identified bioluminescence in five previously unstudied octocoral species, the researchers applied ancestral state reconstruction analysis to investigate the lineage.
“Using the knowledge that contemporary octocoral species exhibit bioluminescence allows us to statistically estimate the likelihood of their ancestors possessing the same feature,” Quattrini elucidates.
Remarkably, a range of statistical methods all point to the same conclusion: the common ancestor to all octocorals was bioluminescent over 540 million years ago. This period is significant for the evolution of eyes in marine invertebrates, raising the possibility that bioluminescence was an important evolutionary force in Cambrian oceans.
Yet, a conundrum remains: if this ancestral octocoral had bioluminescence, why is it so rare among their contemporary descendants? This question will be the focus of future research, potentially unlocking insights into the complex ecosystems of ancient seas.
The study has been documented in the journal Proceedings of the Royal Society B Biological Sciences.
FAQs
- What is bioluminescence?
Bioluminescence is the production and emission of light by a living organism, resulting from chemical reactions within their bodies. - Which organisms are known to be bioluminescent?
Bioluminescence has evolved in a wide range of organisms, including some species of fish, jellyfish, insects, and deep-sea corals, to name a few. - Why do animals use bioluminescence?
Bioluminescence is used for a variety of purposes, such as attracting prey, deterring predators, communication, and camouflage. - How ancient is the trait of bioluminescence according to this study?
The study identified the trait of bioluminescence in octocorals dating back 540 million years ago during the Cambrian period. - What are octocorals?
Octocorals are a type of soft coral characterized by their eight-fold symmetry, with polyps that typically have eight tentacles each.
Conclusion
The revelation that bioluminescence dates back to the Cambrian period some 540 million years ago represents a significant leap in our understanding of ancient marine ecosystems and the evolution of life on Earth. This discovery by DeLeo and her colleagues places the origin of this fascinating adaptation much further back in time than previously understood. As research continues, it may answer lingering questions about the evolutionary pathways bioluminescence took and its varied roles in the complex interplays of past and present oceanic life.