Octopus Genome Reveals Secrets to Complex Intelligence

The largest invertebrate genetic code unleashes clues to camouflage, suckers, evolution

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The has finally been untangled, which should allow scientists to discover answers to long-mysterious questions about the animal's alienlike physiology: How does ? How does it control——those eight and ? And, most vexing: How did a relative of the snail get to be —able to learn quickly, solve puzzles and even ?

, published today in , reveal a vast, unexplored landscape full of novel genes, unlikely rearrangements—and some evolutionary solutions that look remarkably similar to those found in humans. ( is part of Nature Publishing Group.)

With the largest-known genome in the invertebrate world—similar in size to (2.7 billion base pairs) and with more genes () than humans (20,000 to 25,000)—the octopus sequence has long been known to be large and confusing. Even without a genetic map, these animals and their cephalopod cousins (squids, cuttlefishes and nautiluses) have been common subjects for neurobiology and pharmacology research. But a sequence for this group of mollusks has been "sorely needed," says , a cephalopod researcher at Portland State University who was not involved in the new research. "Think about trying to assemble a puzzle, picture side down," she says of octopus research to date. "A genome gives us a picture to work with."

Among the biggest surprises contained within the genome—eliciting exclamation point–ridden e-mails from cephalopod researchers—is that octopuses possess a large group of familiar genes that are involved in developing a complex neural network and have been found to be enriched in other animals, such as mammals, with substantial processing power. Known as genes, they "were previously thought to be expanded only in vertebrates," says , an associate professor of neurobiology at the University of Chicago and a co-author of the new paper. Such genes join the list of independently evolved features we share with octopuses—including camera-type eyes (with a lens, iris and retina), closed circulatory systems and large brains.

Having followed such a vastly different evolutionary path to intelligence, however, the octopus nervous system is an especially rich subject for study. "For neurobiologists, it's intriguing to understand how a completely distinct group has developed big, complex brains," says of the University of Puerto Rico's Institute of Neurobiology. "Now with this paper, we can better understand the molecular underpinnings."

Part of octopuses' sophisticated wiring system—which extends beyond the brain and is largely distributed throughout the body—controls . Researchers have been unsure how octopuses , the pigment-filled sacs that expand and contract in milliseconds to alter their overall color and patterning. But with the sequenced genome in hand, scientists can now learn more about how this flashy system works—an enticing insight for neuroscientists alike.

Also contained in the octopus genome (represented by the California two-spot octopus, ) are numerous previously unknown genes—including novel ones that help the octopus "taste" with its suckers. Researchers can also now peer deeper into the past of this rarely fossilized animal's evolutionary history—even beyond their divergence with squid some 270 million years ago. In all of that time octopuses have become adept at (known as RNA editing, which occurs in humans and other animals but at an extreme rate in octopuses), helping them keep nerves firing on cue at extreme temperatures. The new genetic analysis also found genes that can move around on the genome (known as ), which might play a role in boosting learning and memory.

One thing not found in the octopus genome, however, is evidence that its code had undergone wholesale duplication (as the genome of vertebrates had, which allowed the extra genes to acquire new functions). This was a surprise to researchers who had long marveled at the octopus's complexity—and repeatedly stumbled over large amounts of repeated genetic code in earlier research.

The size of the octopus genome, combined with the large number of repeating sequences and, as Ragsdale describes, a "bizarre lack of interest from many genomicists," made the task a challenging one. He was among the dozens of researchers who banded together in early 2012 to form the , "to address the pressing need for genome sequencing of cephalopod mollusks," as they noted in published later that year in .

The full octopus genome promises to make a splash in fields stretching from neurobiology to evolution to engineering. "This is such an exciting paper and a really significant step forward," says Lindgren, who studies relationships among octopuses, which have evolved to inhabit all of the world's oceans—from warm tidal shallows to the freezing Antarctic depths. For her and other cephalopod scientists, "having a whole genome is like suddenly getting a key to the biggest library in the world that previously you could only look into by peeking through partially blocked windows."

Scientific American .

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