Octopuses have been hiding a dark secret.

Their remarkable intelligence and ability to change color or skin textures at will has made the cephalopods a beloved subject of study – but scientists have now revealed another unique trait that is far grimmer than the ones we’ve become familiar with.

After reproducing, female octopuses begin a dramatic death spiral, starving themselves and eventually wasting away, dying by the time her eggs hatch. And, they typically kill and eat their mates.

In captivity, some even go to great lengths to speed up the process, tearing off their own skin or eating tips of their tentacles.

Now, a new study using genetic sequencing tools has identified the mechanism that controls their gruesome final days.

After reproducing, female octopuses begin a dramatic death spiral, starving themselves and eventually wasting away, dying by the time her eggs hatch. And, they typically kill and eat their mates

According to the study from the University of Chicago Medical Center, the organ behind the female octopus’s death spiral is essentially the cephalopod version of the pituitary gland seen in humans.

Brandeis University psychologist Jerome Wodinsky first showed back in 1977 that removing the octopus’s optic gland caused the females to abandon their eggs, resume feeding, and even go on to mate again.

The new work builds upon this discovery, using genetic sequencing tools to describe the molecular signals produced by the gland after the octopus reproduces to bring about her demise.

‘We’re bringing cephalopod research into the 21st century, and what better way to do that than have this unveiling of an organ that has historically fascinated cephalopod biologists for a long, long time,’ said lead researcher Z. Yan Wang.

‘These behaviors are so distinct and so stereotyped when you actually see them.

‘It’s really exciting because it’s the first time we can pinpoint any molecular mechanism to such dramatic behaviors, which to me is the entire purpose of studying neuroscience.’

After researchers sequenced the genome of the California two-spot octopus in 2015, members of the team also went on to study their unusual maternal behaviors.

While non-mated females are active predators, those who have reproduced keep a close watch on their eggs. After about four days, they stop eating, and their health begins to decline.

The process can last upwards of eight days, during which time they separate from their eggs more frequently, and will even slam themselves into the corners of the tank.

As they deteriorate, their skin gets pale and their muscle tone dwindles.

‘This is troubling to even witness in the lab, because from a human perspective they look like they’re self-mutilating,’ Wang said.

‘It’s just very, very strange behaviour.’

According to the study from the University of Chicago Medical Center, the organ behind the female octopus’s death spiral is essentially the cephalopod version of the pituitary gland seen in humans

The researchers collected the optic glands from octopuses during each of the different stages, and sequenced the RNA transcriptomes.

This revealed that non-mated females produced high levels of neuropeptides. After mating, however, these plummeted.

They also found that the genes which produce neurotransmitters called catecholamine experienced a spike in activity.

These genes are linked to metabolism, showing for the first time a link between the optic gland and a process other than reproduction.

While it’s unclear what exactly these changes do, the researchers say they may affect the energy the octopus expends to find prey.

‘Before when we only knew about the optic gland, it felt like watching the trailer to a movie,’ Wang said.

‘You get the gist of what’s going on, but now we’re beginning to learn about the main characters, what their roles are and a little bit more about the backstory.’

HOW DO OCTOPUSES DEFEND THEMSELVES?

One of the most effective ways octopuses avoid predation is by camouflaging with their environment.

They have special pigment cells allow them to control the colour of their skin, much like chameleons.

As well as colour change they can manipulate the texture of their skin in order to blend in with the terrain. 

As well as camouflage they can escape predators by using a 'jet propulsion' method of escape, where they rapidly shoot out water to propel them through the water rapidly.  

The jet of water from the siphon is often accompanied by a release of ink to confuse and evade potential enemies.

The suckers on the tentacles of the eight-legged beasts are extremely powerful and are used to drag prey towards a sharp beak.

As well as protection from other animals, it has been recently found that octopuses can detect the ultrasonic waves that preempt a volcanic eruption or earthquake, giving them enough time to escape.

Why octopuses meet such a gruesome end remains a mystery.

But, many suspect it could be a way to prevent them from eating their young, as octopuses are known to be cannibals.

‘It’s very strange to see as humans because we reproduce more than once and live way past our reproductive age,’ Wang said.

‘But if the whole purpose of living is to pass along your genes, maybe it’s not so dark.’