The world’s first genetic study of giant squid has uncovered a surprising finding: these monsters of the deep appear to all be members of the same species, Architeuthis dux. Using specimens from 43 squid, researchers looked at mitochondrial DNA inherited along the maternal line to evaluate the differences between them, and were astounded to learn that squid in locations as far flung as Japan and Florida were effectively identical, despite the fact that they may look very different. This research provides an important piece of information about giant squid, and illustrates how much more we have to learn about them.
Long known as figures of myth, giant squid weren’t captured alive on film until the 21st century, although their bodies periodically washed ashore and were found in the bodies of whales. Researchers knew they were widely distributed throughout the world’s oceans and that they lived in deep water, but they didn’t know that much more about them. Thomas Gilbert, a biologist, became curious about the genetics of these creatures, rightly assuming that if we understood their genetic lineage, it would provide more information about their genus and evolution.
When he looked into the issue, he found that no one had undertaken a detailed genetic study, and he partnered with researchers around the world to collect tissue samples and analyze them. They expected to see genetic differences varying by region, confirming the theory that there were somewhere between three and 21 giant squid species around the world in distinct populations. Instead, giant squid across the globe clearly all interact with each other and don’t live in isolated groups; any squid, anywhere, could potentially breed with another, and the resulting young could wind up anywhere in the world. The global distribution of a similar species with such minimal genetic diversity is truly remarkable.
There are several explanations for the apparent generic similarity in giant squid. One possible option is a genetic bottleneck caused by a massive recent dieoff that might have severely cut the numbers of squid in the past, resulting in a lack of diversity in modern squid. Changes in the environment, predators, or disease might have swept through the historic squid population, leaving only a limited number to repopulate the species.
A sudden population boom is another theory, and it might have been spurred by the whaling industry, which eliminated the only serious predator faced by giant squid. Larval squid can also travel freely throughout the world’s oceans and don’t necessarily stick close to home, which is another possible explanation.
It’s also possible that all these theories are incorrect, and the truth lies somewhere in the mitochondrial DNA itself. Researchers are making a number of assumptions about the rate of mutations and how mitochondrial DNA work, and it’s possible that the world’s giant squid have some tricks up their sleeves. And that means we need more research to figure out what, exactly, those tricks might be.
Photo credit: NTNU Vitenskapsmuseet