The 'Love Hormone' Helps Some Starfish Turn Their Stomach Inside Out To Eat

How romantic. (Photo: Maurice Elphick, Queen Mary University of London)

Here’s a reminder that biology is oftentimes more complicated than headlines can make it out to be. Scientists in the UK have found evidence that the so-called “love hormone” oxytocin plays a very different role in starfish than it does in humans and other animals. In starfish, an oxytocin-type molecule seems to help them turn their stomachs inside out so they can eat.

Oxytocin and its close molecular sibling vasopressin have gotten a lot of press and scientific attention over the years. Some studies have suggested that the production of these hormones in the brain might be important for healthy social functioning across a variety of vertebrate species, from prairie voles to humans. They might even have a similar role in simpler, invertebrate life forms like roundworms (at least, to the extent that worms can socialise and “want” to mate.)

Oxytocin, in particular, has gotten the moniker of the “love hormone” or “moral molecule.” Some research has found that greater levels of it are released when people experience orgasm during sex or in the first exciting months of a new relationship. It’s also been shown to increase trust between people when they’re given more of it via a nasal spray.

But according to the authors, there’s been little research on how these hormones or very similar-looking ones could work in invertebrates like starfish. For all their strangeness, these guys are actually more related to humans than are roundworms.

In 2016, the team published research on their discovery of an oxytocin-type molecule in the starfish species Asterias rubens and dubbed it asterotocin. This time around, they synthesised asterotocin in the lab and dosed the starfish with it.

Compared to the starfish given water (as a control), the starfish given asterotocin responded within 20 minutes by carrying out their very normal but gut-churning feeding routine: getting their bodies into position and pushing their stomachs from an innie to an outtie. In the wild, these starfish use their arms to pull apart shelled animals like mollusks, then wrap their stomach around the fleshy part, dissolve it to death, and suck up the juice back into their bodies.

The findings, published Wednesday in BMC Biology, suggest that something very much like the oxytocin/vasopressin system has existed in animals for an incredibly long time — and that, in at least some branches of the evolutionary tree of life, it’s served a less romantic, if still crucial purpose.

“Our study has provided important new evidence that oxytocin-type molecules are important and ancient regulators of feeding in animals,” said study author Maurice Elphick, a physiologist and neuroscientist at the Queen Mary University of London, in a release from the university. “So oxytocin is much more than a ‘love hormone’ — perhaps especially for animals like starfish that don’t fall in love!”

Flashy headlines aside, it’s well known the effects of these hormones, even in people, go far beyond making us go starry-eyed or more sociable. Oxytocin is already routinely used to help induce labour in pregnant women, and vasopressin helps treat certain medical conditions by constricting blood vessels and making the body retain water. Other research has also started to show that their influences on social behaviour are subtler and more complicated than they first seemed to be.

The researchers, for their part, plan to keep digging deeper into their discovery.

“We want to find out if asterotocin has the same effect in other starfish species e.g. the crown of thorns starfish,” Elphick told Gizmodo via email.

That’s relevant because crown-of-thorns starfish eat coral instead of mussels. And when their populations explode, they voraciously devour and devastate the surrounding marine environment. So if the same basic system exists in these starfishes, it might be possible to manipulate it in reverse and stop their feeding frenzy. But before that, we also need to know how exactly asterotocin interacts with a starfish’s body.

“We want to investigate at a molecular level how asterotocin activates the receptor protein that it binds to, because we are interested in seeing if we can identify a molecule that blocks the effect of asterotocin,” Elphick explained.

As for people, there’s still important work to be done in studying these hormones as a social booster — particularly for those living with conditions like autism spectrum disorder. But it’s also worth keeping in mind that few discoveries in science are ever as simple as they’re chalked up to be.

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