The more we know about them, the more they fascinate us. Its nine brains, for example (one central and another eight peripherals), allow each limb to act independently. Each arm, in fact, can explore, try and react to its environment without consulting with … The central brain. It is also the most intelligent invertebrates that exist, capable of learning, remembering and solving complex problems. And there are even those who consider them extraterrestrial creatures.
And now, the octopuses have just revealed to us another of their secrets: the factors that determine their sex.
A team of researchers from the University of Oregon, in effect, has just identified, in the so -called two points of California (Octopus bimaculoides), a sex chromosome. One that could have 480 million years, even before the octopus separated from nautilus in the evolutionary tree. Which makes it one of the oldest sexual sex chromosomes that are known. The finding also solves the ancient biological mystery of how sex is determined in cephalopods (octopus, capamares, sepias and nautilus).
«Cephalopods -explains Gabby Coffing, co -author of an article recently published in ´Current Biology´– They are already very interesting creatures, and there are many things that we are still learning about them, especially in neuroscience. Our work only shows one more thing: they have really old sex chromosomes. “
The difficult determination of sex
Among mammals, including us, the sex of those who are going to be born is largely determined by chromosomes. But that is not the only means that exists for it. In turtles, for example, the main factor that determines sex is the temperature at which eggs are incubated. And some fish have a specific gene, although not a complete chromosome. Even in humans, the sex chromosomes system x/y is not as clear as it might seem, and genetic mutations, or the fact of inheriting additional sex chromosomes, can lead to the result not always fit with what was expected.
In addition, because cephalopods are not ‘normal’ laboratory animals, such as mice or fruit flies, their genetic exploration is limited. Scientists, in fact, have so far sequenced the genomes of just a handful of octopus species, but not enough to link genes with specific features just as it is done in mice or humans.
Therefore, when the authors of this study sequenced the DNA of a two -point octopus female from California, they ran out of bruces with something they did not expect: a chromosome that contained only half of the genetic material. Something not observed so far and that had not been found in the male octopus DNA previously sequenced.
“This chromosome in particular,” explains Coffing, “half of the amount of sequencing data, indicated that there was only one copy. Then, as we explore more, we concluded that we had stumbled with a sexual chromosome ».
A chromosome with 480 million years
To confirm it, the researchers search in the genomic octopus data available from other studies, many of which were not even clearly labeled as males or females. Even so, they managed to find another sexual chromosome in another kind of octopus, and another in the genome of a squid, a species that separated evolutionarily from the octopus at some point between 248 and 455 million years ago. And in their search, they also managed to find evidence of the sex chromosome in a nautilus, a mollusk that separated from the octopus about 480 million years ago.
The fact that all these species share the same chromosome is the proof that it existed for a long time. “This indicates,” says Coffing, “also his common ancestor had a similar system for determining sex.” Which is unusual among sexual chromosomes, since due to their direct impact on reproductive abilities they are usually subject to a lot of selective pressure, so they tend to suffer rapid evolutionary changes. Cephalopods, however, seem to have found very soon the model that works best, and have stayed with it for hundreds of millions of years.
Until now, other old sex chromosomes had been discovered in some groups of plants, as well as mosses and fungi, which are among the first to evolve. And sexual insect chromosomes can also be 450 million years old. But in all cases, these chromosomes have changed a lot over time.
One less secret, then, on the octopus. Although researchers know that these animals still have many to discover.
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