Click Here for Octopus evolution About the Game: These days, new genomes of different types of organisms are being sequenced and published on a regular basis. When some new genome is sequenced, evolutionary biologists expect that it will be highly similar to the genomes of other organisms that are assumed to be closely related. As ENV already noted, the latest organism to have its genome sequenced has confounded that expectation: the octopus, whose genome was recently reported in Nature . It turns out to be so unlike other mollusks and other invertebrates that it’s being called “alien” by the scientists who worked on that project. Not to send you into a meltdown or anything but octopuses are basically ‘aliens’ — according to scientists. Researchers have found a new map of the octopus genetic code that is so strange that it could be actually be an “alien”. […] “The octopus appears to be utterly different from all other animals, even other molluscs, with its eight prehensile arms, its large brain and its clever problem-solving abilities,” said US researcher Dr Clifton Ragsdale, from the University of Chicago. […] Analysis of 12 different tissues revealed hundreds of octopus-specific genes found in no other animal, many of them highly active in structures such as the brain, skin and suckers. Obviously no one thinks the octopus is an “alien” from another planet. ( Nature News quotes one co-author of the paper on the genome noting that the alien quip is a “joke.”) But it certainly is alien to standard evolutionary expectations that genomes of related species ought to be highly similar. Thus, Nature points out the large number of unique genes found in the octopus genome: Surprisingly, the octopus genome turned out to be almost as large as a human’s and to contain a greater number of protein-coding genes — some 33,000, compared with fewer than 25,000 in Homo sapiens . This excess results mostly from the expansion of a few specific gene families, Ragsdale says. One of the most remarkable gene groups is the protocadherins, which regulate the development of neurons and the short-range interactions between them. The octopus has 168 of these genes — more than twice as many as mammals. This resonates with the creature’s unusually large brain and the organ’s even-stranger anatomy. … A gene family that is involved in development, the zinc-finger transcription factors, is also highly expanded in octopuses. At around 1,800 genes, it is the second-largest gene family to be discovered in an animal, after the elephant’s 2,000 olfactory-receptor genes. The analysis also turned up hundreds of other genes that are specific to the octopus and highly expressed in particular tissues. The suckers, for example, express a curious set of genes that are similar to those that encode receptors for the neurotransmitter acetylcholine. The genes seem to enable the octopus’s remarkable ability to taste with its suckers. Scientists identified six genes for proteins called reflectins, which are expressed in an octopus’s skin. These alter the way light reflects from the octopus, giving the appearance of a different colour — one of several ways that an octopus can disguise itself, along with changing its texture, pattern or brightness. The technical paper explains that the octopus genome reveals “massive expansions in two gene families previously thought to be uniquely enlarged in vertebrates: the protocadherins, which regulate neuronal development, and the C2H2 superfamily of zinc-finger transcription factors.” Moreover: We identified hundreds of cephalopod-specific genes, many of which showed elevated expression levels in such specialized structures as the skin, the suckers and the nervous system. They conclude: “Our analysis suggests that substantial expansion of a handful of gene families, along with extensive remodelling of genome linkage and repetitive content, played a critical role in the evolution of cephalopod morphological innovations, including their large and complex nervous systems.” In other words, the cephalopod genome is unusual in many major respects, unlike other organisms we’ve sequenced. Actually, that’s not completely correct. There are some peculiar similarities between the cephalopod genome and something else they’ve seen — but they aren’t the kind of similarities that were predicted by common descent. octopus evolution hack
