Newly Sequenced Giant Squid Genome Raises as Many Questions as It Answers

By George Dvorsky on at

One the most intriguing and mysterious creatures on the planet – the giant squid – has finally had its genome fully sequenced. But while the genome is helping to explain many of its distinguishing features, including its large size and big brain, we still have much to learn about this near-mythical beast.

“A genome is a first step for answering a lot of questions about the biology of these very weird animals,” Caroline Albertin, a co-author of the new GigaScience study and a geneticist at the Marine Biological Laboratory at the University of Chicago, said in a press release.

Indeed, little is known about the giant squid, due to its skittish nature and because it lives at such great depths. To date, not a single giant squid has been captured alive, so much of its biology remains a mystery. The only specimens that have been studied are carcasses that washed ashore or were accidentally hauled up by fisherman, and sightings in the wild have been limited to spooky, teasing glimpses taken by underwater cameras.

But now, in an important development, scientists have a fully sequenced giant squid genome.

Engraving of a giant squid stranded in 1877 on Trinity Bay, Newfoundland. (Image: Unknown/Wikimedia)

“Having this giant squid genome is an important node in helping us understand what makes a cephalopod a cephalopod,” said Albertin. “And it also can help us understand how new and novel genes arise in evolution and development.”

In total, the researchers identified approximately 2.7 billion DNA base pairs, which is around 90 per cent the size of the human genome. There’s nothing particularly special about that size, especially considering that the axolotl genome is 10 times larger than the human genome. It’s going to take some time to fully understand and appreciate the intricacies of the giant squid’s genetic profile, but these preliminary results are already helping to explain some of its more remarkable features.

For example, Albertin and her colleagues identified a group of genes called reflectins, which are only known to exist in cephalopods. It’s a key finding, as colour is an an essential element of camouflage.

“Reflectins are a family of proteins that are only found in cephalopods, such as squid, cuttlefish, and octopus,” said Albertin in an email to Gizmodo. “They are involved in making the iridescence in the skin and the eyes, and most cephalopods, including the giant squid, have several of these genes.”

Because reflectins are only found in cephalopods, biologists can only study them in this group of animals, she said. Only a handful of cephalopods have been sequenced, “so the giant squid genome will be able to help us to understand the biology of this family of proteins,” explained Albertin.

A giant squid measuring over 4 metres (13 feet) long. (Image: NASA)

The scientists also identified genes responsible for growth and development, namely the Hox and Wnt genes. These genes might play a role in this animal’s gigantism, as individuals typically grow to between 9 and 13 metres in length (30 to 42 feet). That said, their size doesn’t appear to be the result of whole-genome duplication, an evolutionary growth strategy seen in large-bodied vertebrates.

“Whole genome duplication has been described in a number of different groups of organisms,” Albertin told Gizmodo. “Some plants are famous for this, but vertebrates – animals with a backbone – also had a whole genome duplication that has been hypothesised to be important in their evolution. We don’t see evidence for whole genome duplication in any of the cephalopods examined thus far, including the giant squid.”

As to how the giant squid got to be so big remains an unanswered question.

Giant squids also have large brains, which we can only assume are as complex as those seen in other cephalopods. And indeed, the researchers identified well over 100 genes in a grouping known as protocadherins, which aren’t typically found in invertebrates.

“For a long time, we thought that having a lot of protocadherins was only found in vertebrates, so we were really surprised when we found more than 160 of them in the octopus genome,” said Albertin, in reference to her 2015 paper on the subject. “We have found an expansion of protocadherins in the giant squid as well, which has the largest invertebrate brain. We don’t yet know what they are doing, but it could be a clue to how you make a complicated brain,” she told Gizmodo.

Most of the genes seen in the giant squid are shared with other animals, like octopuses, snails, worms, flies, and humans, so this genome will now serve as an important reference point for scientists when comparing it to other cephalopods and animals, and for studying the giant squid’s unique features, said Albertin.

The scientific quest to learn more about giant squids continues. Thankfully, and as Albertin pointed out, marine biologists who study giant squids and related species are now equipped with a powerful new resource to help them learn more.

Featured image: David McNew (Getty Images)