Solitary, shy, and incredibly intelligent, the octopus is one mysterious animal. But researchers trying to get at what makes the cephalopod tick now have another tool at their disposal: The entire octopus genome.
An international team of biologists and geneticists reports that they have sequenced the first entire octopus genome. They published the genome of the California two-spot octopus this week in the journal Nature.
Octopuses are particularly fascinating creatures to study at a genetic level because they’re so different from other animals—even from other cephalopods, a group that also includes squid and cuttlefish. They have no skeleton, three hearts, incredible camouflage skills, and tentacles that can regenerate. Moreover, those eight arms are home to most of their nearly half-billion neurons. That's five times as many neurons as a mouse has. An octopus is about as smart as a dog.
"The octopus appears so utterly different from all other animals, even ones it’s related to, that the British zoologist Martin Wells famously called it an alien,” as study co-author Clifton Ragsdale describes. "In that sense, you could say our paper describes the first sequenced genome from an alien."
Parts of the octopus taken for tissue analysis as part of the sequencing process. Image Credit: Albertin et al., Nature (2015)
The researchers identified hundreds of cephalopod-specific genes, many of which showed elevated expression levels in specialized structures such as its color-changing skin, strong suckers, and complex nervous system. The octopus genome also has several notable characteristics that distinguish it from other invertebrates, including much larger sets of two gene families involved in brain and neuronal development. Intriguingly, these larger sets were previously thought to be unique to vertebrates.
In another surprise, the researchers discovered that the octopus's large genome size was not due to whole genome duplication events, which can be seen in the genomes of vertebrates including humans, according to a statement by the Okinawa Institute of Science and Technology, one of the teams involved in the research. Such events create additional genetic material for evolution to work with.
However, the octopus genome shows no evidence of whole genome duplication in its evolutionary history, which is ancient. (Based on a "relaxed" molecular clock, which measures the number of mutations that accumulate in the gene sequences of different species over time, the researchers estimate octopus and squid lineages diverged about 270 million years ago.)
Understanding the genetics behind the octopus's unique abilities may one day help bioengineers in their quest to improve octopus-inspired technology such as camouflage, robot arms, and suction cups. In the meantime, scientists will continue to study brainy octopuses like Scooty, a California two-spot octopus who lives at the University of Chicago, another institution involved in the study. An overview of the genome study—and adorable footage of Scooty—is in the video below.