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Micro RNAs: A New Clue About Octopus Intelligence?

While octopus brains are very different from vertebrate brains, they share with vertebrates, a huge number of microRNAs
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In general, the “intelligent” animals (apes, elephants, crows, whales, dogs, dolphins) are vertebrates, not invertebrates. There is one glaring exception: the cephalopods (octopuses, squid, cuttlefish). They, like vertebrates, developed large, complex brains and unexpectedly sophisticated cognitive abilities.

coconut octopus underwater macro portrait on sand

When thinking about the puzzle, we sometimes fall victim to a sort of confusion: We reason that greater intelligence results from the fact that it “helps the octopus survive better.” Perhaps it does. But, while greater intelligence might help many life forms survive better, only a few develop it. In short, we need a “how” explanation here, not a “why” explanation.

A recent study from the Max Delbrück Center for Molecular Medicine points to the possible role of microRNAs (miRNAs). MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression after genes have been transcribed. They are considered powerful regulators of activities like cell growth, differentiation, development, and death. Octopuses have

… a massively expanded repertoire of microRNAs (miRNAs) in their neural tissue – reflecting similar developments that occurred in vertebrates. “So, this is what connects us to the octopus!” says Professor Nikolaus Rajewsky, Scientific Director of the Berlin Institute for Medical Systems Biology of the Max Delbrück Center (MDC-BIMSB), head of the Systems Biology of Gene Regulatory Elements Lab, and the paper’s last author. He explains that this finding probably means miRNAs play a fundamental role in the development of complex brains.

Max Delbrück Center for Molecular Medicine in the Helmholtz Association, “What octopus and human brains have in common” at Eurekalert (November 25, 2022) The paper is open access.

That probably isn’t the whole story of intelligence but some features are very suggestive:

The most interesting discovery was in fact the dramatic expansion of a well-known group of RNA genes, microRNAs. A total of 42 novel miRNA families were found – specifically in neural tissue and mostly in the brain. Given that these genes were conserved during cephalopod evolution, the team concludes they were clearly beneficial to the animals and are therefore functionally important…

“This is the third-largest expansion of microRNA families in the animal world, and the largest outside of vertebrates,” says lead author Grygoriy Zolotarov, MD, a Ukrainian scientist who interned in Rajewsky’s lab at MDC-BIMSB while finishing medical school in Prague, and later. “To give you an idea of the scale, oysters, which are also mollusks, have acquired just five new microRNA families since the last ancestors they shared with octopuses – while the octopuses have acquired 90!” Oysters, adds Zolotarov, aren’t exactly known for their intelligence.

Max Delbrück Center for Molecular Medicine in the Helmholtz Association, “What octopus and human brains have in common” at Eurekalert (November 25, 2022)

Ways octopuses are smart but weird — and very different

Octopuses are unusual in that they have both a central brain and a nervous system that controls the tentacles that can act independently. The central brain is not at all like ours:

The construction of the octopus eye itself is like our own, but that’s where the similarity ends. Behind the eye, the octopus’ brain is wildly different from mammalian brains in terms of architecture and design, yet it uses similar building blocks and accomplishes the same tasks…

For a team of neuroscientists in Oregon, understanding this invertebrate brain is both fascinating and informative. “The sensor is really similar, but the brain that’s processing the information is completely different,” explained Cris Niell, professor of biology and neuroscience at the University Oregon.

Bradley van Paridon, “Mapping the octopus brain” at Advanced Science News (November 22, 2022) The paper is open access.

How different? Much information doesn’t even go through the brain:

Now, in a new study published on November 28 in Current Biology, Hale, William Rainey Harper Professor of Organismal Biology and Vice Provost at UChicago, and her colleagues have described something new and totally unexpected about the octopus nervous system: a structure by which the intramuscular nerve cords (INCs), which help the animal sense its arm movement, connect arms on the opposite sides of the animal.

University of Chicago Medical Center, “Unique features of octopus create ‘an entirely new way of designing a nervous system’” at Eurekalert (November 28, 2022) Paper.

And another study found that the octopus uses different neurotransmitters from vertebrates.

The octopus brain and nervous system has been called a “second genesis” of intelligence. That raises an interesting issue: If intelligence was a fluke when it was generated once, as some claim, what about finding it generated again in a different neurological format? When flukes repeat themselves, something else is usually going on.

Note: This year, researchers spotted octopuses throwing things at each other: “Underwater cameras captured the cephalopods collecting shells, silt and algae with their arms and hurling them at one another by using jets of water from their siphon to propel the scraps. The researchers even observed the receiving octopuses ducking to avoid a hit.” (Scientific American, December 7, 2022)

You may also wish to read: Octopuses get emotional about pain, research suggests. The smartest of invertebrates, the octopus, once again prompts us to rethink what we believe to be the origin of intelligence. The brainy cephalopods behaved about the same as lab rats under similar conditions, raising both neuroscience and ethical issues.

Denyse O'Leary

Denyse O'Leary is a freelance journalist based in Victoria, Canada. Specializing in faith and science issues, she has published two books on the topic: Faith@Science and By Design or by Chance? She has written for publications such as The Toronto Star, The Globe & Mail, and Canadian Living. She is co-author, with neuroscientist Mario Beauregard, of The Spiritual Brain: A Neuroscientist's Case for the Existence of the Soul. She received her degree in honors English language and literature.

Micro RNAs: A New Clue About Octopus Intelligence?