Worms are decomposers. Many survive by breaking down dead things — dead bacteria, dead plants, dead animals, dead anything. So, they must be accustomed to the stench of death. Not so, a new study suggests — not when the dead organism is another worm.
Published in Current Biology, the study states that C. elegans roundworms react adversely to the smell of a deceased counterpart. Not only does this smell invoke a behavioral response of corpse avoidance, but it also invokes a physiological response of increased short-term fertility and decreased long-term fitness and lifespan.
“Caenorhabditis elegans prefers to avoid dead conspecifics,” or deceased members of the same species, the authors state in the study, with the worms reacting to death with a range of “aversion” and “survival” responses. Taken together, the results reveal a new signaling mechanism that’s available to worms and possibly other organisms, too, as a means of detecting and responding to death.
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Worms Signal and Detect Death
C. elegans roundworms aren’t the only small organisms that respond to the dead. Ants and bees dispose of the deceased from their colonies, for instance, while fruit flies avoid corpses (and shun flies that have seen corpses themselves). Death-exposed fruit flies even experience faster aging after seeing a deceased counterpart, and have shorter lifespans than those that have had no encounters with death.
That these animals respond so strongly to the dead is widely documented. So, when the authors of the new study noticed C. elegans worms wriggle away from corpses, they saw the response as a chance to dig deeper into death signaling and detection. Indeed, while many species’ reactions to death are mediated mainly by sight, that certainly wasn’t the case for wiggling roundworms, which have no eyes and no sense of vision.
“We felt this was quite a unique opportunity to start diving into what is happening mechanistically that enables C. elegans to detect a dead conscript,” said Matthias Truttmann, a senior study author and a physiologist at the University of Michigan, according to a press release.
To determine how C. elegans worms detect the dead, Truttman and his team exposed the worms to conspecific corpses and to fluids taken from the deteriorating cells of those corpses. The worms responded to both with avoidance, moving away regardless of their age and sex, suggesting that the corpses and fluids carried similar signatures of death.
These death cues also resulted in short-term increases in fertility, long-term decreases in fitness (represented by a reduced thrashing rate), and long-term decreases in lifespan. But what were those death cues, exactly, and how did the worms pick up on them?
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Sounding a Sensory Alarm
To figure out what those cues could be, the study authors recorded the activity in the worms’ sensory neurons as they encountered the corpses and fluids. The recordings revealed that AWB and ASH, two neurons that are responsible for making sense of olfactory stimuli, were activated when the corpses and fluids were present, indicating that the worms were smelling the signature of death.
“The neurons we identified are well known to be involved in behavioral responses to a variety of environmental cues,” Truttmann said in the release.
According to the study authors, the metabolites AMP and histidine were probably responsible for the signal of death that the C. elegans worms recognized. Though these metabolites are typically contained in living cells, they are released when living cells die and deteriorate — in this case, triggering the behavioral and physiological responses in C. elegans.
“They also detect a couple of intracellular metabolites that are not typically found in the environment. If they are around, it indicates that a cell has died, popped open, and that something has gone wrong,” Truttmann said in the release.
It is possible that cellular metabolites serve as a signal of death in other organisms, too, Truttmann said, as the release of metabolites from dying and disintegrating cells in one tissue can cause changes in other tissues in humans, for instance.
Whether this signal sounds the alarm in other organisms is still uncertain. While further research is required to understand the role of cellular metabolites in detecting death across species, for now, it’s clear that death is a sensitive subject, even for worms like C. elegans.
Read More: Animals Respond to Death in Many Ways. Mourning Might Be One of Them
Article Sources
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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
