Octopuses tragically destroy themselves after mating. We can finally know why

Octopuses are doomed to be orphans from a very young age. After a female octopus lays her eggs, she stops eating and begins to self-mutilate, ripping her skin off and biting the ends of her tentacles.

By the time a young octopus wriggles out of its egg, its mother is already dead. A few months later, your father will also die.

The octopus’ short and dark life has long fascinated scientists. In 1944, researchers hypothesized that mating was somehow hitting a molecular “self-destruct” button within sea creatures.

It took nearly 80 years, but this vague hypothesis is finally taking shape. Researchers recently discovered that mating appears to change several critical biochemical pathways based on cholesterol and various hormones in female octopuses.

“We know that cholesterol is important from a dietary point of view and also within different signaling systems in the body,” explains molecular biologist Z. Yan Wang, who led the research at the University of Chicago.

“It’s involved in everything from the flexibility of cell membranes to the production of stress hormones, but it was a big surprise to see it play a role in this life cycle process as well.”

Among humans, some cholesterol precursors are toxic at high levels. Genetic disorders that increase cholesterol metabolism can therefore result in serious behavioral and developmental problems, including repetitive self-harm and dietary deficiencies. Severe cases can even be fatal.

The symptoms are eerily reminiscent of female octopuses in their final days, which suggests the researchers may be finding something out.

It took years to get here, and in large part it’s because of a small, underappreciated organ found in octopus and squid.

In 1977, researchers discovered that the optic gland somehow plays a role in the programmed death of an octopus.

This organ is similar to the pituitary organ in humans. It sits between the octopus’ eyes and is linked to sexual development and aging in cephalopods. When removed from a female octopus, the creature lives for several months after laying its eggs.

In 2018, scientists took this knowledge and sequenced RNA from two optic glands from two female octopuses in different stages of decline.

As an octopus neared death, the authors noticed higher levels of activity in several genes that control sex hormones, insulin-like hormones, and cholesterol metabolism.

Now, a few years later, some of the same researchers have directly analyzed the molecules secreted by this organ in both mated and unmated females.

After mating, it appears that the optic gland actually secretes more sex hormones, insulin-like hormones, and cholesterol precursors.

All three of these molecules could contribute to signaling systems that trigger death. Or maybe it’s just the accumulation of these molecules in the octopus’ body that is lethal, as is the case with humans.

Although the optic gland has previously been linked to sex hormone production in cephalopods, the other two pathways have only recently been identified in the “self-destruction” sequence.

In the future, Wang and his colleagues hope to look further “downstream” to see what other molecules are part of this oddly timed death.

“What is impressive is that [octopuses] go through this progression of changes where they seem to go crazy right before they die,” says neurobiologist Clifton Ragsdale of the University of Chicago.

“Maybe it’s two processes, maybe three or four. We now have at least three seemingly independent pathways to steroid hormones that might explain the multitude of effects these animals show.”

Wang says she’s particularly excited because two of the pathways her team identified are known from other rodent studies.

“[N]Now there is evidence from our study that these pathways are likely also present in octopuses,” says Wang.

“It was really exciting to see the similarity between such different animals.”

The study was published in Current Biology.

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