(CN) - Scientists have unlocked genetic secrets of the elusive octopus, finding striking differences with other invertebrates and more than 3,500 genes believed to be specific to the alien-like creature.
Octopuses, shy and intelligent, live for about 8 years. They perform remarkably well on intelligence tests involving mazes and other challenges, and are said to be able to recognize the scientists who work with them.
Now an international team of scientists has sequenced the genome of the California two-spot octopus - the first cephalopod ever to be fully sequenced. They discovered novel genes, unlikely rearrangements, and some evolutionary solutions that appear remarkably similar to those found in humans.
"The octopus appears to be utterly different from all other animals, even other mollusks, with its eight prehensile arms, its large brain and its clever problem-solving capabilities," said co-senior author Clifton Ragsdale, associate professor in the Departments of Neurobiology and Organismal Biology and Anatomy at the University of Chicago.
"The late British zoologist Martin Wells said the octopus is an alien. In this sense, then, our paper describes the first sequenced genome from an alien," Ragsdale said.
Octopuses, along with squids, cuttlefish and nautiluses, are cephalopods, an order of predatory mollusks with an evolutionary history of more than 500 million years, long before plants moved onto land.
The octopus has long been recognized as a remarkable creature, with its eight sucker-lined arms that can regrow, cameralike eyes, a large and elaborate brain, and skin that has the ability to camouflage by changing its color and texture.
Cephalopods are the most intelligent invertebrate and have demonstrated learning behaviors and elaborate problem-solving abilities, such as figuring out how to open a food-filled jar.
Ragsdale and his colleagues sequenced the California two-spot octopus, a relatively small species that dwells off the coast of Southern California, to study the genetics of these specialized traits. They published their findings in the Aug. 12 issue of the journal Nature.
The research reveals striking differences between the genome of the octopus and other invertebrates, including huge expansions in two families of genes previously thought to be unique to vertebrates, and a complex gene arrangement.
The octopus's genome is nearly the size of the human genome and much larger than those of other sequenced invertebrates such as snails or oysters. Of its 33,000 genes, approximately 3,500 are found only in the octopus. Many of these unique genes are active in the brain, suckers, retina and in its sophisticated camouflage system.
The most notable of the expansion of genes was in the protocadherins, a family of genes that are involved in developing complex neural networks such as those found in mammals.
These genes were previously thought to be expanded only in vertebrates, but the researchers found that the octopus genome contains 10 times more of these genes than other invertebrates and more than twice as many as mammals.
"We expected to be surprised," Ragsdale said of the findings. "These are such remarkable animals."
Another gene family discovered in the genome - the zinc finger transcription factors - are involved in embryonic and nervous tissue development. The octopus genome contained the 1,800 of these transcription factors, which is the second-largest gene family discovered so far in animals.
The researchers also found that while the octopus gene families are similar to other invertebrates, their genetic arrangements are drastically different.
