Stuff Of Legend: Monstrous Giant Squid’s Genome Revealed, But Many Questions Remain

WOODS HOLE, Mass. — Sailors and seafarers have told terrifying tales of giant squids (Architeuthis dux) consuming entire ships whole for centuries. Across generations and cultures, man has long feared these elusive and mysterious creatures. Often referred to as “The Kraken,” giant squids are rarely ever actually seen, and one has never been caught alive, but these incredible beings are very much real. Now, for the first time ever, researchers have put together a preliminary reconstruction of the giant squid’s full genome sequence. These revelations provide new insights into these gigantic creatures’ origins, but also raise entirely new questions.

This groundbreaking project was led by a team of researchers at the University of Copenhagen, including scientist Caroline Albertin, from the Marine Biological Laboratory in Woods Hole, Massachusetts. It’s worth noting that in 2015, Albertin also led a research project that constructed the first genome of a cephalopod (octopus, squid).

Giant squid
The giant squid has long been a subject of horror lore. In this original illustration from Jules Verne’s ‘20,000 Leagues Under the Sea,’ a giant squid grasps a helpless sailor. (Image credit: Alphonse de Neuville)

“In terms of their genes, we found the giant squid look a lot like other animals. This means we can study these truly bizarre animals to learn more about ourselves,” she comments.

Perhaps predictably, the giant squid’s genome is quite large; consisting of an estimated 2.7 billion DNA base pairs, making it about 90% the size of the human genome.

Researchers analyzed numerous ancient, well-studied gene families in the giant squid’s DNA, finding many similarities to four other cephalopod species, as well as the human genome.

Perhaps the project’s most notable finding was this: within the giant squid, essential developmental genes that are found almost universally in all animals were only present in single copies. This indicates that giant squids did not develop to such an unbelievably large size through the process of whole-genome duplication. This evolutionary process is essentially how all vertebrates, including humans, have increased in size over time.

So, the question then becomes, if the kraken didn’t become so big through these means, how did it grow to such mythical proportions?

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Even besides this major conundrum, there are many more questions that remain unanswered. Such as how it developed the largest known brain among invertebrates, its incredibly intelligent and sophisticated behavior, and its camouflage skills that far outclass any of its fellow cephalopods.

“A genome is a first step for answering a lot of questions about the biology of these very weird animals,” Albertin says.

“While cephalopods have many complex and elaborate features, they are thought to have evolved independently of the vertebrates. By comparing their genomes we can ask, ‘Are cephalopods and vertebrates built the same way or are they built differently?” She continues.

Another odd observation: over 100 genes were detected in the giant squid’s genome of the protocadherin family. These genes are not often seen among invertebrates.

“Protocadherins are thought to be important in wiring up a complicated brain correctly,” Albertin explains. “They were thought they were a vertebrate innovation, so we were really surprised when we found more than 100 of them in the octopus genome (in 2015). That seemed like a smoking gun to how you make a complicated brain. And we have found a similar expansion of protocadherins in the giant squid, as well.”

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

The study is published in GigaScience.

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