'Love hormone' has stomach-turning effect in starfish

According to a new study by Queen Mary University in London, a hormone released into our brain when we fall in love also turns the stomachs of starfish upside down to feed them.

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Oxytocin, more commonly referred to as the "love hormone", is important for sexual reproduction in humans, other mammals and even nematode worms, but this study shows that it is important for feeding common European starfish (Asterias rubens).

The results, published in the journal BMC Biology, could play an important role in controlling the feeding behaviour of the starfish thorn crown (Acanthaster planci), which feeds on coral and has a devastating impact on the Australian Great Barrier Reef.

Thanks to this study, researchers know that oxytocin molecules have been active in the nervous system of animals for more than half a billion years.

However, the effects on feeding can be very different depending on the type of animal - starfish oxytocin molecules appear to be important for normal feeding, while studies in mice have shown that oxytocin inhibits feeding behaviour.

Professor Maurice Elphick, lead author of the Queen Mary University of London study, said: "Our study has provided important new evidence that oxytocin molecules are important and long-standing regulators of animal nutrition. Oxytocin is therefore much more than a "love hormone" - perhaps especially for animals like starfish that do not fall in love!"

Esther Odekunle, a former doctoral student at Queen Mary University in London, added: "If the love hormone plays a role in the feeding behaviour of the starfish thorn crown, then this research could serve as a basis for developing new chemical methods to control their taste for coral.

Within minutes, the injected starfish began to bend its arms and adopt a "bumpy" posture similar to the posture used when it feeds. In addition, starfish have knocked their stomachs out of their mouths.

This was an interesting combination of effects because starfish feed naturally by climbing on prey such as mussels or oysters and adopting a rigid, bumpy posture so that they can use the pulling force of many small tubular feet on the underside of each arm to separate the two valves from their prey.

After creating a tiny hole, the starfish then turns its stomach out of its mouth, through the hole and into the prey's body - where it digests the prey's soft tissues in a soup-like mixture, which is then returned to the starfish as food.

When all the prey's tissues have been digested, the starfish withdraws its stomach into its mouth, leaving an empty shell behind it and moving away to find its next victim.

Professor Elphick said, "What is fascinating is that the injection of the hormone into starfish induces what is called a fictional diet. Starfish behave as if they were feeding on a mussel or oyster, but no mussel or oyster is there to be eaten."

The researchers found that the effect of the hormone is so powerful that it slows down the starfish by 2 to 3 times when it is turned upside down. This is an important defensive behaviour in nature because they can be reversed by strong waves.

What they also discovered is that the hormone and its receptor are found in many parts of the starfish body, including the central nervous system and stomach. These results are consistent with the striking effects of the oxytocin-like molecule on the behaviour of starfish.