麻豆淫院

When the nematode worm Caenorhabditis elegans gets caught by its fungal predator Arthrobotrys oligospora, it doesn't just wriggle endlessly鈥攊t suddenly "freezes," stopping all movement and feeding as if going into a deep rest.

A new study from Academia Sinica, Taiwan, and the Max Planck Institute for Biology in T眉bingen has investigated the neural and molecular mechanisms behind this behavior. It revealed how the worm's sense of touch and a key brain signaling system work together to trigger this freeze response. The findings are in the journal iScience.

"This striking behavior 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."

The nematode C. elegans offers unique advantages in studying predator鈥損rey dynamics, thanks to its simple nervous system, transparency, well-known genetics, and short life cycle. It is arguably the best-characterized animal species on Earth and a powerful tool for investigating the molecular, genetic, and behavioral mechanisms of survival strategies in response to predation, allowing the team to probe the neurons and signals involved precisely.

The basic behavioral 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鈥損rey 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) signaling 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 signaling acting together reveal how animals carefully detect and respond to predators with complex behaviors," 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 behavior 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 immobilization response. Is this behavior 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.