Worm mothers ‘sacrifice themselves’ by providing milk for their young, scientists find

Certain worm mothers “sacrifice themselves” for their young by providing them with milk which destroys their own organs, scientists have discovered.

The nematode worm, Caenorhabditis elegans, has long been studied by scientists seeking to understand more about the ageing process, thanks to its simplicity and genetic similarities with humans.

As a result, the new findings published in Nature Communications could have far-reaching implications for the search for how to slow human ageing.

Most of the one millimetre-long transparent roundworms have both male and female reproductive organs, and the mothers reproduce by fertilising themselves with limited stocks of self-sperm. When these run out, within days of sexual maturity, reproduction stops.

The worms then behave in a way which has puzzled scientists for some time – they generate large quantities of yolk-rich fluid which accumulates in large pools inside their bodies and destructively consumes their internal organs in the process.

They also lay more than their own body weight in unfertilised eggs.

Scientists previously assumed these changes were futile and represented some form of old-age disease state – but have now found a purpose for both.

“Once we realised that the post-reproductive worms were making milk, a lot of things suddenly made sense,” said the study’s first author Dr Carina Kern, from University College London’s Institute of Healthy Ageing.

“The worms are destroying themselves in the process of transferring nutrients to their offspring. And all those unfertilised eggs are full of milk, so they are acting like milk bottles to help with milk transport to feed baby worms.”

Scientists suggested the discovery shows a “unique” act in which the worms “maximise their evolutionary fitness”.

Self-destructive and life-shortening reproductive effort of this sort is typical of organisms such as Pacific salmon that exhibit suicidal reproduction. The new study suggests C. elegans lifespan may also be limited by suicidal reproduction.

“We have now explained a unique self-destructive process seen in nematode worms,” explained lead author Professor David Gems, also from the UCL.

“It is both a form of primitive lactation, which only a few other invertebrates have been shown to do, and a form of reproductive suicide, as worm mothers sacrifice themselves to support the next generation.”

Dr Kern added: “The existence of worm milk reveals a new way that C. elegans maximise their evolutionary fitness: when they can't reproduce anymore because they have run out of sperm, they melt down their own tissues in order to transfer resources to their offspring.”

Given how central the creatures are to scientific research into ageing, the findings could have significant implications for our prospects of being able to slow the human ageing process, the researchers suggested.

“The amazing thing about ageing in C. elegans is that lifespan can be massively increased by gene manipulation – up to 10-fold,” said Dr Gems. “This suggests that by understanding how this happens, one could find the key to slowing human ageing, which is really exciting.

“But if C. elegans' life extension is just due to suppression of suicidal reproduction like in salmon, then the possibility of applying our knowledge of worm ageing to dramatically extend human life suddenly looks remote.”

However, the researchers believe there is still more to learn about human ageing from C. elegans, and in an accompanying journal article presented evidence that suicidal reproduction has evolved from more general mechanisms of ageing, and that causes of ageing-related disease are similar in both C. elegans and other animals, including humans.

Professor Gems said: “In the end, what is critically important is to understand the principles that govern the process of C. elegans ageing and explain the causes of age-related disease more generally.

“We don’t yet understand this for any organism. But for C. elegans we are getting there, and the discovery of worm milk gets us another step closer.”

Additional reporting by PA

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