Giant squids are probably one of the rarest animals in the planet -- so rare, that it made its way through folklore as something monstrous that attacks ships and eating innocent fishermen. However, even though the giant squid gets a horrendous reputation, there is nothing intimidating about this mollusk -- except maybe, its size. Biologists are still trying to figure out how did the giant squid reached this almost gargantuan size.
It was only until recently that important clues about the anatomy and the evolution of the giant squid were somehow understood when a team of scientists from the University of Copenhagen and Marine Biological Laboratory, Woods Hole published the complete genome sequence of the creature. This genome sequence is largely helpful since giant squids are rarely been seen and have never been caught and kept alive. Caroline Albertin of the Marine Biological Laboratory, Woods Hole explains that in terms of their genes, the giant squid is pretty much like other animals, meaning, they can be studied easily as they have similarities with other animals. The team, which was led by Rute da Fonseca of the University of Copenhagen, discovered that the giant squid genome, like everything else in the creature, is big: it comprises an estimated 2.7 billion DNA base pairs. This is about 90% of the size of the human genome.
With the help of Albertin's experience in cephalopod genome sequencing, they were able to analyze several ancient and well-known gene families in the giant squid. The team was also able to compare the genome to four other cephalopod species that have been sequenced with the human genome. Albertin found out that Hox and Wnt genes -- the most important developmental genes in almost all animals -- are present in single copies only in the genome of the giant squid, meaning the large cephalopod did not attain its size through whole-genome duplication unlike how vertebrates attained their large sizes throughout their evolution. It seems figuring out how the giant squid becomes enormous is a concern that shall be investigated in the future.
According to Albertin, a genome is the first step for answering questions about the biology of bizarre animals such as the giant squid. For instance, through analyzing their genome, one can get answers on how the giant squid acquired the largest brain among invertebrates or how they developed their sophisticated behavior and agility as well as their incredible camouflage. "While cephalopods have many complex and elaborate features, they are thought to have evolved differently from vertebrates," Albertin explains.
Albertin and the team were also able to identify more than 100 genes in the protocadherin family. These cell-adhesion proteins are abundant in mammals but not in invertebrates which is why it is quite surprising to find it in the giant squid genome. Albertin explains that protocadherins are important in wiring up complicated brains correctly. They were thought to be an evolutionary innovation of the vertebrates. "That seemed like a smoking gun to how you make a complicated brain but we have found a similar expansion of protocadherins in the giant squid."
Caroline Albertin was also able to analyze a gene family that is unique to cephalopods which they called reflectins. According to her, reflectins are able to encode proteins that are involved in making iridescence. "Color is an important part of camouflage, so we are trying to understand what exactly this gene family is doing." Albertin also explained that having this giant squid genome is an important step in understanding what makes a cephalopod unique and how novel genes arise in evolution and development.
