The elusive giant squid—a 10-armed invertebrate said to have dragged ships to the ocean floor—has finally had its genome fully sequenced.
Important clues about the anatomy and evolution of the mysterious Architeuthis dux have been revealed by a team of scientists from the universities of Copenhagen and Chicago.
“These new results may unlock several pending evolutionary questions regarding this mantled species,” according to research lead Rute de Fonseca, an associate professor with the Center for Macroecology, Evolution, and Climate (CMEC) at the University of Copenhagen’s Globe Institute.
Giant squid—estimated to grow up to 43 feet from posterior fins to the tip of two lengthy tentacles—is second only to the colossal squid, which, at an approximate 46 feet long, is one of the largest living organisms.
In 2004, Japanese researchers took the first images of a live giant squid in its natural habitat; additional video sightings have confirmed their existence in Asia and North America.
But no sea serpents have been caught and kept alive, so their biology remains a secret to scientists.
Until now.
Scale of size between human and giant squid (via Center for Macroecology, Evolution, and Climate/Globe Institute/ University of Copenhagen)
It turns out the giant squid’s genome is also, well, giant: With an estimated 2.7 billion DNA base pairs, it’s about 90 percent the size of the human genome.
“In terms of their genes, we found that the giant squid look a lot like other animals,” Caroline Albertin, of the University of Chicago’s Marine Biological Laboratory (MBL), said in a statement. “This means we can study these truly bizarre animals to learn more about ourselves.”
As described in a paper published in the journal Oxford Academic, important developmental genes present in almost all animals (Hox and Wnt) exist only in single copies in the giant squid genome.
That means this titanic invertebrate, long a source of sea-monster lore, did not grow through whole-genome duplication—a strategy evolution assumed long ago to increase the size of vertebrates.
How it did, however, remains unclear.
“A genome is a first step for answering a lot of questions about the biology of these very weird animals,” Albertin said.
Questions like how they acquired the largest invertebrate brain, sophisticated behaviors and agility, and the knack for instantaneous camouflage.
Giant squid sucker rings (via Trustees of the Natural History Museum)
“While cephalopods have many complex and elaborate features, they are thought to have evolved independently of the vertebrates,” she continued. “By comparing their genomes we can ask, ‘Are cephalopods and vertebrates built the same way or are they built differently?'”
Despite challenges in the lab (i.e. uncooperative samples), the team also identified more than 100 genes in the protocadherin family within the giant squid genome, and analyzed the reflectins gene family that, so far, is unique to cephalopods.
“Having this giant squid genome is an important node in helping us understand what makes a cephalopod a cephalopod,” Albertin said. “And it also can help us understand how new and novel genes arise in evolution and development.”
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