Bioluminescence has evolved at least 27 separate times in fish.
Trillions of glowing fish can be found in the dark depths of the ocean. A new study published in the journal PLOS ONE shows that bioluminescence — the ability of a living creature to produce light — is so incredibly useful that it has evolved in fish 27 separate times.
Researchers analyzed DNA from over 300 types of ray-finned fish to identify the various points of origin of bioluminescence in their family tree.
Among the luminous fish that they studied were species with shining fishing poles dangling from their heads, ones with bright lanterns beneath their eyes, and ones that radiate light from their bellies. Some produce their glow intrinsically through genetic or chemical mechanisms, while others have formed permanent partnerships with light-producing bacteria.
"When things evolve independently multiples times, we can infer that the feature is useful," said study co-author W. Leo Smith, assistant curator at the University of Kansas Biodiversity Institute, in a press release.
"You have this whole habitat where everything that's not living at the top or bottom of the ocean or along the edges — nearly every vertebrate living in the open water — around 80 percent of those fish species are bioluminescent. So this tells us bioluminescence is almost a requirement for fishes to be successful."
The researchers found that bioluminescence in these fish started evolving around 150 million years ago. Once a lineage had assumed the ability to produce light, it tended soon thereafter to branch into many new species, according to the study.
"Many fish proliferate species when they evolve this trait — they differentiate, but we don't know why," Smith said.
Luminous fish can use their light to lure prey, hide from predators, and even communicate with one another.
Smith suggests one reason why these fish have been so successful is that in the ocean where there are no physical barriers like rivers or mountains to separate groups of fish from each other, bioluminescence may help fish identify members of their own species as potential mates. This would draw clear boundaries among species, allowing them to differentiate from each other, and thus become more numerous over time.
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