A DNA study on the elusive giant squid, using tissue samples from the Natural History Museum's famous Archie specimen, has revealed there is just one species, scientists report this week.
Although only being filmed in its natural habitat for the first time at the end of 2012, the cephalopod has been spotted all over the world, except in tropical and polar regions. However, scientists didn't know if these were separate species or not, and people have previously suggested there might be 3 or 21 giant squid species.
In order to find out, a team including Inger Winkelmann and Prof Tom Gilbert of the University of Copenhagen carried out molecular analysis on 43 giant squid samples.
Museum scientists preparing the giant squid. Its 2 feeding tentacles are much longer than the arms.
They were able to include tissue samples from the Museums 8.62m giant squid specimen, Archie, because it is one of the rare complete specimens that was caught live rather than recovered from a beach or the stomach of a sperm whale.
From these samples the team analysed the mitochondrial DNA, which are the energy structures in every cell that contain their own DNA and that are inherited through the mother.
Their results indicate that the giant squid has very low genetic diversity. Individuals tested from the furthest regions of the world are virtually the same genetically. This suggests that there is just one species of giant squid, Architeuthis dux, worldwide.
They also found no difference in the structure of populations living far apart, so for example individuals in Japan are no more closely related to each other than they are to those in Florida.
‘To have it confirmed that there is only one species of giant squid that lives in all the world’s oceans is a great find,’ says Museum squid curator Jon Ablett who organised the preservation and storage of the Museum's giant squid in 2004. ‘It also shows the importance and potential of museum specimens for molecular and life history studies such as this.’
‘We have specimens in our collections that have washed up around the UK to as far away as the Falklands Islands, and it is surprising yet exciting to find out that these are all the same species.’
The team says that the low genetic diversity may be explained by population bottlenecks or sudden population inflation in the recent past. So, regional populations may have been prone to large fluctuations in size or even extinctions followed by re-population from neighbouring areas.
The findings are typical of a highly migratory species, says the team. Previous studies have suggested that adult giant squid do not travel great distances, so Winklemann says migration is likely to happen during the squid's larval stage when they are dispersed throughout the world's ocean currents.
The study is published in the journal Proceedings of the Royal Society Biology.