A chemical signal tells starfish they’re full

New research just published in the journal eLife found that starfish, like us, have a chemical signal that tells them to stop eating. Despite this similarity, starfish feed in a very strange way. The animal everts it’s stomach, pushing the organ out of the mouth, to digest food outside of the body cavity. 

“Starfish exhibit one of the most remarkable feeding behaviors in the animal kingdom – they evert their stomach out of their mouth and digest large prey externally, and once the prey has been digested, the stomach is withdrawn,” wrote the study authors.

While it was known that a hormone similar to oxytocin in humans signals the beginning of eating among starfish, it was not known what called for an end to food consumption. 

To investigate, the researchers used the common starfish (Asterias rubens) as a research subject. The scientists injected the feeding starfish with SK/CCK-type neuropeptides, a hormone that inhibits appetite in both humans and insects. When the hormone was injected, the starfish retracted their stomachs. Even when offered their favorite food – a mussel – the starfish refrained from eating. 

Dr. Ana Tinoco, one of the lead authors of the study, explained why this finding was interesting.

“The unusual way that starfish feed where they evert their stomachs out of their mouths, makes them a good model to study chemicals that regulate feeding processes.” 

“Whilst we already knew that this type of hormone was important for feeding, what’s fascinating is that the important role of these chemicals in feeding in other animals has been preserved in starfish despite their dramatically different feeding behaviour, lack of a brain and unique body plan.”

The study shows that the regulation of eating is conserved among animals, as starfish occupy a unique place as an evolutionary stepping stone between invertebrates and vertebrate animals. The researchers hope that this study may help in the development of new drugs to help treat eating disorders.  

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By Zach Fitzner, Earth.com Staff Writer