No sci-fi alien is as strange as an octopus

Tuesday, May 2nd, 2017

“No sci-fi alien is so startlingly strange” as an octopus, Sy Montgomery noted, but they’re even stranger than we realized:

Rosenthal and Eisenberg found that RNA editing is especially rife in the neurons of cephalopods. They use it to re-code genes that are important for their nervous systems — the genes that, as Rosenthal says, “make a nerve cell a nerve cell.” And only the intelligent coleoid cephalopods — octopuses, squid, and cuttlefish — do so. The relatively dumber nautiluses do not. “Humans don’t have this. Monkeys don’t. Nothing has this except the coleoids,” says Rosenthal.

It’s impossible to say if their prolific use of RNA editing is responsible for their alien intellect, but “that would definitely be my guess,” says Noa Liscovitch-Brauer, a member of Rosenthal’s team who spearheaded the new study. “It makes for a very compelling hypothesis in my eyes.”


Only about 3 percent of human genes are ever edited in this way, and the changes are usually restricted to the parts of RNA that are cut out and discarded. To the extent that it happens, it doesn’t seem to be adaptive.

In cephalopods, it’s a different story. Back in 2015, Rosenthal and Eisenberg discovered that RNA editing has gone wild in the longfin inshore squid — a foot-long animal that’s commonly used in neuroscience research. While a typical mammal edits its RNA at just a few hundred sites, the squid was making some 57,000 such edits. These changes weren’t happening in discarded sections of RNA, but in the ones that actually go towards building proteins — the so-called coding regions. They were ten times more common in the squid’s neurons than in its other tissues, and they disproportionately affected proteins involved in its nervous system.

Having been surprised by one cephalopod, the team decided to study others. Liscovitch-Brauer focused on the common cuttlefish, common octopus, and two-spot octopus. All of these showed signs of extensive RNA editing with between 80,000 to 130,000 editing sites each. By contrast, the nautilus — a ancient cephalopod known for its hard, spiral shell — only had 1,000 such sites.

This distinction is crucial. The nautiluses belong to the earliest lineage of cephalopods, which diverged from the others between 350 and 480 million years ago. They’ve stayed much the same ever since. They have simple brains and unremarkable behavior, and they leave their RNA largely unedited. Meanwhile, the other cephalopods — the coleoids — came to use RNA editing extensively, and while evolving complex brains and extraordinary behavior. Coincidence?

Liscovitch-Brauer also found that around 1,000 of the edited locations were shared between the coleoid species — far more than the 25 or so sites that are shared between humans and other mammals. These sites have been preserved over hundreds of millions of years of evolution.


  1. An interesting co-incidence in the life histories of octapods, 8-limbed creatures being rare, is that both the octopus and the spider have the same, uncommon, maternal behaviour, laying eggs and staying with them and tending them till death, when the eggs hatch.

  2. Bruce says:

    I suspect octopi and squids have been overhunted to a shadow of what they used to be by cetacea.

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