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Nematode worms enter a sleep-like state when captured by predatory fungi, shedding light on ancient survival strategies.
When Caenorhabditis elegans, a model nematode worm, gets caught in the sticky traps of the predatory fungus Arthrobotrys oligospora, it rapidly stops moving and feeding, entering a sleep-like dormant state. Researchers have uncovered the neural circuits and molecular pathways behind this dramatic behavioural shift, revealing a sophisticated mechanism that could be critical for predator-prey interactions.
Short Overview
1. Predation-induced freezing behaviour: Caenorhabditis elegans trapped by fungal predator Arthrobotrys oligospora triggers a sleep-like state, until it stops moving and feeding after an initial struggle.
2. Sensory and signalling mechanisms: This behaviour is mediated by mechanosensory neurons sensing touch – activating the sleep-promoting neurons ALA and RIS, and EGFR signalling in the brain. Mechanosensory neurons and epidermal growth factor receptor (EGFR) signalling pathways are critical for the fungal trap-induced quiescence response.
3. Ecological and evolutionary insights: These findings reveal how prey integrate mechanosensory and sleep-related neuronal pathways to respond behaviourally to predation stress, providing insights into predator-prey coevolution.
When the nematode worm Caenorhabditis elegans gets caught by its fungal predator Arthrobotrys oligospora, it doesn’t just wriggle endlessly—it suddenly “freezes,” stopping all movement and feeding as if going into a deep rest. The study from Academia Sinica, Taiwan, and the Max Planck Institute for Biology in Tübingen investigated the neural and molecular mechanisms behind this behaviour. It revealed how the worm’s sense of touch and a key brain signalling system work together to trigger this freeze response.
“This striking behaviour between C. elegans and the nematode-trapping fungi caught our attention immediately and triggered our investigation,” says lead researcher Yen-Ping Hsueh, Director of the Department for Complex Biological Interactions. “We saw the worms initially struggling relentlessly for 15 to 20 minutes after being trapped, then suddenly stopping, as if they ‘gave up.’ This prompted us to explore the underlying nervous systems involved in this ‘freezing’ response.”
Using the nematode C. elegans unique advantages in studying predator-prey dynamics, thanks to its simple nervous system, transparency, well-known genetics, and short life cycle. It is arguably the best-characterised animal species on Earth and a powerful tool for investigating the molecular, genetic, and behavioural mechanisms of survival strategies in response to predation, allowing the team to probe the neurons and signals involved precisely.
The basic behavioural observation of stress-induced sleep from predation was reported back in the 1960s. “The real opportunity came when both the worm and the fungus became easy to study with genetics, so we could finally dig into both sides of this predator-prey story,” explained first author, Tzu-Hsiang Lin.
Exploring the Neural Mechanisms Behind Survival Strategies
The team discovered that C. elegans activates specific sleep-promoting brain cells known as ALA and RIS neurons to induce the quiescence, or resting state. Crucially, this process depends on the nematode’s mechanosensory neurons that detect the physical stimulus of being trapped, plus an epidermal growth factor receptor (EGFR) signalling pathway known from other stress responses.
This freezing isn’t just any type of rest. “It’s a unique trigger of a sleep-like state caused by physically being caught by a predator,” explains Tzu-Hsiang Lin. “The worm uses the same EGFR alarm system for other dangers, like being wounded or overheated. It’s activated by being physically caught. The worm senses the trap through touch, and then it sends a signal to the worm’s brain, which makes them stop moving, almost like falling asleep.”
The findings highlight how ancient and versatile survival strategies are conserved at the cellular level. “Mechanosensation and EGFR signalling acting together reveal how animals carefully detect and respond to predators with complex behaviours,” Hsueh adds. “This opens a new window into how brains integrate external threats with internal states like sleep.”
When asked about next steps, Lin shared, “We have a few questions we want to answer: Who does freezing help? We need to figure out if this behaviour actually helps the worm survive or if it just helps the fungus get its meal. What’s the trigger? We’re interested in what other signals or chemicals might be involved in this immobilisation response. Is this behaviour universal? We want to see if other nematodes freeze when caught by different predatory fungi. This will tell us if it's a common strategy. If some worms react differently, we want to understand why and what makes them more or less likely to freeze.”
This research not only uncovers how nematodes adapt to deadly fungal traps but also enriches our understanding of sleep and stress responses across species. It illustrates how even the smallest animals evolve sophisticated strategies to survive and thrive.
Director
Department of Complex Biological Interactions
Dr. Yen-Ping Hsueh
ping-hsueh@tuebingen.mpg.de
Press Office
Beatriz Lucas
presse-bio@tuebingen.mpg.de
Lin, T.-H., Chang, H.-W., Tay, R. J., & Hsueh, Y.-P. (2025). Predation by nematode-trapping fungus triggers mechanosensory-dependent quiescence in Caenorhabditis elegans. iScience, 28, 112792. https://doi.org/10.1016/j.isci.2025.112792
https://www.bio.mpg.de/480706/news_publication_25360932_transferred
https://keeper.mpdl.mpg.de/d/5798c97764fa4924a9d1/
https://www.bio.mpg.de/391832/complex-biological-interactions
The survival strategy of “freezing” when trapped by a predator
Copyright: Tzu-Hsiang Lin / Max Planck Institute for Biology Tübingen, Germany
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