Deep-sea monsters have surprising DNA

Giant squid, which can grow to an astounding 43 feet long, have equally extraordinary DNA, a new study concludes.

The long-awaited report, published in the Proceedings of the Royal Society B, finds that there is “exceptionally low” genetic diversity among giant squid from around the world.

“These observations are consistent with the hypotheses that there is only one global species of giant squid, Architeuthis dux,” wrote Inger Winkelmann and colleagues, who suggested that the squid could have one of the largest known ranges of any species.

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Little is known about giant squid, which can live some 3,300 feet below the surface. Mostly we know about them from fantasy adventure books, like “20,000 Leagues Under the Sea,” and images of them dead, with their long tentacles dangling far beyond the picture frame. Giant squid are rarely captured alive, with most found stranded on beaches or seen floating dead on the water’s surface. Unfortunately, some are also retrieved by fisheries as by-catch .

Winkelmann, from the University of Copenhagen’s Natural History Museum of Denmark, and colleagues studied the mitochondrial genome of tissue samples from 43 such giant squid. “Mitochondrial” refers to a type of DNA inherited only through the female line. The squid came from all over the world, including waters off of California, Florida, Spain, Japan and New Zealand.

Incredibly, all had the same basic mitochondrial genomes. If there is just one giant squid species, as the researchers suspect, then adults must travel huge distances. Younger squid might disperse via drifting.

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Giant squid might also be more plentiful than previously thought. But the lack of genetic diversity could make this species more vulnerable to human impact. Back in the day, fishermen rarely encountered the deep-dwelling squid. Now, with modern trawling equipment and huge fishing operations, the squid are more likely to become by-catch.

Pollution and climate change could also hurt the squid, as could loss of their food sources. They are thought to primarily feed on deep sea fish and other, smaller types of squid.