Giant Squid DNA Reveals Secrets of Global Family Ties

In the depths of the ocean live the creatures that may have inspired stories about the Kraken and other mythological beasts: giant squid. Yet while these massive animals roam across the world's oceans, it turns out that their DNA is more similar than scientists expected. In fact, new research shows that the squid have more genetic similarities than other marine animals, hinting that they intermingle and mate across the globe.

Despite their size, giant squid are an elusive species. In fact, it wasn't only until this year that a video of a giant squid was released to the public, and no one had actually observed a live giant squid in the wild until 2004. Growing up to about 60 feet in length, the giant squid possesses the largest eyes in the animal kingdom, measuring about 10 inches in diameter. The eyes allow them to detect objects and prey in the dark depths of the ocean where little to no light reaches.

In order to learn more about the squid and possible subspecies, scientists extracted DNA from 43 soft-tissue samples from giant squid. While some samples came from squid that were found in whale stomachs and washed ashore, others came from frozen samples from squid that were caught by fishing trawlers.

Giant squid vary greatly in appearance. While the average giant squid possesses a thin body and long arms, the squid found off of the coast of Japan are much shorter and have stubbier tentacles. Scientists estimated that there could be as many as eight distinct species of giant squid based on the appearances of specimens that have been found.

The results of the study, though, showed the complete opposite. After examining the mitochondrial DNA found in tiny cell structures called mitochondria in the soft tissue samples, the researchers realized that the squid were all one species. In fact, the mDNA sequences were extremely similar among all samples with more than 20 times less genetic diversity than other local squid populations. This means that not only are giant squid all one species, but they're also all part of the same big population--the squid interact with each other equally instead of smaller groups interacting only with others in the same group.

In the future, researchers hope to confirm the results using nuclear DNA from the giant squid. Using this DNA, they hope to rule out the possibility that the similarities in mDNA could have been some quirk of evolution. Yet if the results hold, it's very likely that the giant squid could have undergone a recent population expansion.

"We speculate the larval stage must drift globally in the currents then dive to the nearest dark, deep spot when they are large enough, thus stopping any [population] structure appearing," said M. Thomas P. Gilbert, one of the researchers, in an interview with BBC News. "Instead of the adults and their young living in the same place, the young distribute to a completely new place on Earth every time."

The study is published in the Proceedings of the Royal Society B.