From face-to-face sex to friendly cooperation at mealtime, nobody expected the Larger Pacific Striped Octopus to display so many strange behaviours – save for one man.

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Rodaniche's original drawing of the LPSO. Image: Rodaniche/PLoS ONE

In the 1970s, a biologist named Arcadio Rodaniche was working at the Smithsonian Tropical Research Institute in Panama when he became familiar with a curious type of octopus. The researcher noticed that the species displayed some odd characteristics, especially when it came to its social behaviour, but most of those observations would remain buried away for decades. That's because the original attempt to describe the species was rejected, and until now, never attempted again.

For over 25 years, Rodaniche’s observations, which intrigued generations of cephalopod biologists, were the only ones ever made on living Large Pacific Striped Octopuses (LPSOs). In fact, hardly anyone in the scientific community had ever seen one. But in a new study, published this week in the journal PLoS ONE, a team of researchers led by UC Berkeley scientist Roy L. Caldwell have changed that completely. 

"In 2012–2014 we were able to obtain several live specimens of this species, which remains without a formal description," he explains. It's as if the species had been lost and suddenly rediscovered.

Together with Rodaniche (now retired and mostly making marine biology-inspired art), the team combined the original 1970s observations with a new, more detailed set, taken on 24 LPSOs caught off the coast of Nicaragua, and studied in captivity. Because they were able to carefully observe the octopuses in a laboratory environment, the researchers managed to formally document the behaviours that Rodaniche claimed, nearly forty years ago, set them apart from every other known octopus species.

For one thing, they mate beak-to-beak, with the male sometimes becoming completely enclosed within his partner’s arms. When other octopuses take up a beak-to-beak stance, it’s almost always during an aggressive interaction, but for LPSOs it appears friendly.

Octopus sex is perhaps a bit shocking to those unfamiliar with the courtship rituals of squishy invertebrates. Males have a modified arm called a hectocotylus and on it grow row upon row of sperm-containing packets called spermatophores. When a male finds a willing female, he deposits his arm inside one of her oviducts (the tube leading to the ovary) and releases his genetic contribution to their future offspring. Sometimes, he rips his arm off so the female can carry it around with her and store it for later (to use at a time that’s perhaps more convenient). In other species, female octopuses have been known to strangle and devour the males once the deed is done. 

Because female octopuses have two oviducts, they are actually capable of mating with two males at once. But that’s not possible in the LPSO’s beak-to-beak position. The researchers best guess is that a beak-to-beak mating monopoly means less competition for the male. And interestingly, they don't appear worried about becoming the females' next meal.

That brings us to another surprise. Shallow-water octopuses usually give up mating and sometimes even eating while they protect their eggs. After they lay their eggs, they start the transition into life as elderly octopuses. And around the time that their offspring hatch, they die. But not the LPSO. Females of this species deposit their eggs over the course of six months, and continue to guard them (a process called “brooding”) for another eight months before aging takes its toll. Since they’re willing to continue mating even while brooding, it’s possible that the species developed the creative sex position to allow the females to multi-task.

Caldwell and his team also observed male and female octopuses sharing their dens for the first time. In a remarkable instance of cooperation, they saw a mated pair share a piece of food, each octopus sitting (again in a beak-to-beak formation) at either end of the den chewing opposite ends of the snack, Lady and the Tramp style.

It could be that individual LPSOs are able to recognise each other, a feat that would explain the relatively friendly interactions that seem so unique for a group of animals known for cannibalising each other. That could be related to their group living in the wild. SCUBA divers who captured LPSOs for the researchers reported being able to return to the same spots over and over again to find large aggregations of the tentacled beasts, sometimes 30 to 40 at one site.

“This observation suggests group site fidelity, which might extend beyond the life span of a single individual,” explains the team. And if they indeed are able to recognise each other, that could likewise explain their stunning and unusual skin colouration and patterns.

When Rodaniche first attempted to publish his work on the LPSO, the behaviours he described were so far removed from the conventional understanding of octopus behaviour that he was likely dismissed without much thought by the biologists reviewing his work. What other surprising secrets are hiding in nature and in forgotten filing cabinets, patiently waiting to be dusted off and rediscovered? 

Top header image: Roy L. Caldwell