There has long been a missing chapter in the story of cephalopod evolution. That’s how a squid-like ancestor gave rise to today’s octopus. It turns out that the answer has been floating in the deep ocean all along.
The elusive vampire squid (Vampyroteuthis infernalis), with its ghostly glowing eyes, eight arms resembling its octopus cousin, and a deep ruby color to match, has finally revealed its genetic secrets.
In a study published Nov. 27 in the journal iScience, researchers sequenced the genome of Vampyrotheuthis and found that despite belonging to the order Octopus, its chromosomes still resemble those of squid and cuttlefish. This discovery suggests what the common ancestor of modern squids and octopuses looked like at the genetic level 300 million years ago, when octopuses and squids diverged evolutionarily. Researchers described the vampire squid as a “living fossil.”
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In the evolutionary tree of cephalopods, vampire squids belong to the group that includes octopuses, but they underwent a “very ancient split” from the rest of the clade, study lead author Oleg Simakov, a researcher at the Department of Neuroscience and Developmental Biology at the University of Vienna in Austria, told Live Science via email.
After the researchers obtained tissue samples from vampire squid caught as bycatch in the western Pacific Ocean on research expeditions, they used a genetic analysis platform called PacBio to sequence the samples’ DNA. Unfortunately, due to rarity, there were no other vampire squid samples available for comparison. The researchers used PacBio to compare the vampire squid’s genome to that of other cephalopods, including Argonauta hians, Octopus vulgaris, and Eledone cirrhosa.
The discovery reveals that the vampire squid has a genome 11 billion base pairs long, almost four times the length of the human genome, making it the largest cephalopod genome ever sequenced.
Although the DNA of modern octopuses is constantly being replaced, resulting in chromosome mixing, researchers have found that the vampire squid’s genome retains many of the chromosome sequences similar to its ancestral squid. Essentially, it is an tacopod, genetically similar to ancient squid.
Vampire squid have a long and misunderstood history. When it was first discovered in 1903, it was thought to be a curly octopus because of the distinctive webs between its arms. However, in the 1950s scientists reclassified it as its own group, belonging to the suborder Vampire, rather than octopus or squid. It got its name because it looks like it wears a vampire-like cloak.
Bruce Robison, a senior scientist at the Monterey Bay Aquarium Research Institute (MBARI), who was not involved in the study, said the discovery was welcome news for cephalopod scientists and was “glad to find out” why vampire squid retain many of the traits similar to their squid ancestors.
A fully sequenced genome is so valuable in part because of how difficult vampire squid are to study, Robison said, “mainly because they live in difficult-to-access habitats, are solitary and rare, and don’t survive well in captivity.” “Some people think they can dive deep and find it whenever they want, but that is simply not the case.”
He added that the discovery “confirms what some people think that vamps are the key to the puzzle. Vamps are interesting to study because they’re such cool animals and they seem to be hiding secrets.”
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