Scientists have sequenced the octopus genome for the first time, unlocking several secrets of the elusive and unusual creature. In a study published Wednesday in the journal Nature, scientists said that their research revealed striking differences between octopus and other invertebrates, shedding light on how these creatures evolved and opening doors to future studies into the development of complex nervous systems.
The creature has been long considered an unusual specimen to biologists, who have been fascinated by the cephalopod's multiple prehensile arms that can regrow and their complex color-changing mechanisms. They are also one of the most sophisticated and intelligent animals known, as they can learn new behaviors, exhibit problem-solving methods like figuring out how to open a jar and playing, all of which indicate elevated brain functioning.
The octopus boasts the largest-known genome among all invertebrates, similar in size to a house cat, and with more genes than humans. The genomes of other cephalopods, including squids and mollusks, are well-documented and commonly used in neurological research.
A team of researchers from the University of Chicago, University of California, Berkeley, and Japan's Okinawa Institute of Science and Technology analyzed the genome of the Octopus bimaculoides, also known as the California two-spot octopus.
One of their most surprising findings was the presence of protocadherin genes -- a large network of genes that are involved in developing complex neural networks like those found in mammals. These genes "were previously thought to be expanded only in vertebrates," co-author Clifton Ragsdale of the University of Chicago told Scientific American. In fact, the researchers found that protocadherins are 10 times more common in octopus genes than in mammals.
However, in comparison to mammals, the octopus evolved its neural network under completely different circumstances. "For neurobiologists, it's intriguing to understand how a completely distinct group has developed big, complex brains," Joshua Rosenthal of the University of Puerto Rico, who contributed data to the research, reportedly said. "Now with this paper, we can better understand the molecular underpinnings."
Another gene family discovered in the genome, zinc-finger transcription factors, also plays a role in the functioning and development of the octopus' nervous system.
They found that the octopus had genetic arrangements drastically different from other invertebrates, with its nervous system extending well beyond its brains and into its tentacles. They suspect that the advanced wiring is responsible for several of its impressive features, including its instantaneous camouflage and shape-shifting abilities.
The sheer size of the octopus genome, and the presence of several sections that seem to be repeated, coupled with what Ragsdale called a "bizarre lack of interest from many genomicists," made the task of genome sequencing more difficult. But he added that the new findings should spur interest into the creature’s unusual genetic structure.
"Once we pass into a post-genomic age, as we have for octopus, it opens a whole new range of questions, and new abilities to ask how the nervous system is organized, how it develops," he said in a press release.