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Giant squids? They’re just 1 species

By Kai Kupferschmidt
ScienceNOW
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Fifteen years ago, biologist Thomas Gilbert walked into a store in Britain and, on an impulse, picked up a book about giant squid, creatures he knew almost nothing about.

Years later, sick in bed, he finally read the work – only to learn that the rest of the world knew remarkably little about them as well. That’s when Gilbert, an expert on ancient DNA at the Centre for GeoGenetics at the Natural History Museum of Denmark in Copenhagen, resolved to help answer some questions about these creatures.

Now, Gilbert and colleagues from all over the world have analyzed the genetics of giant squid for the first time. The data “corroborates what has been said earlier using morphological criteria,” said Steve O’Shea, an expert on giant squids who worked at Auckland University of Technology in New Zealand: There is only one species, globally distributed, of giant squid.

The also deepen the mystery surrounding these enigmatic creatures. The researchers found startlingly little genetic variation, raising questions about the species’ recent history.

Giant squid are deep-ocean creatures that can weigh hundreds of pounds and measure more than 300 feet from their posterior fin to the tips of their two long tentacles. Although they have been found in all of the world’s oceans and feature heavily in marine lore, a live giant squid wasn’t photographed until 2002.

The international team of researchers used 43 samples of giant squid tissue from around the globe – from the coasts of Spain and South Africa to the South Pacific and the Sea of Japan. Some of the animals had been found stranded on the shore or floating on the sea; others were captured by trawlers or even discovered in the stomach of a sperm whale.

“Getting this material together was actually one of the hardest parts,” Gilbert said. “I’m not a cephalopod biologist, so in the beginning people were reluctant to give me these precious samples.”

The team analyzed DNA from the animals’ mitochondria: small, energy-producing structures inside a cell. Despite the geographic range, the scientists found almost no genetic differences between individuals.

The mitochondrial genome, a ring of more than 20,000 base pairs, differed in only 181 places over all 43 specimens, the researchers write in the Proceedings of the Royal Society B. “It’s completely bizarre,” Gilbert said. “How can something be global but have so little variation?”

The remarkable lack of variation supports the theory that there is just one species of giant squid.

In the past, researchers have proposed up to eight separate species, based largely on the morphology of the animals’ beaks, and many researchers have assumed there are at least three distinct geographic species.

The results “support what has been said many times earlier by some and contradicted by others, and debated by a few,” O’Shea said.

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