How nematodes sense danger
In critical situations, communication can mean the difference between life and death. If our house goes up in flames, we don’t need to smell smoke to be alarmed as long as someone yells, “Fire!” This isn’t unique to humans; even creatures with much less sophisticated means of sharing information have ways of telling each other to watch out.
In the July issue of GENETICS, Zhou et al. report that the nematode Caenorhabditis elegans can sense when members of its kind have been wounded or killed nearby; it actively avoids extracts derived from closely related nematodes but not those of the more evolutionarily distant fruit fly, with which it often shares a habitat. The worms didn’t appear to be harmed by chemicals in the guts of their fallen brethren; exposure to the extracts didn’t decrease the worms’ lifespans, and pain-sensing neurons weren’t needed for the alarm response. But something in the fluids alerted the worms to nearby danger.
This wouldn’t be the first known example of such a signal. Many animal species—and perhaps even humans—communicate about danger using alarm pheromones. Just like in the worms, these chemicals are often species-specific, allowing the animals to detect threats directed at their own kind. In line with the way alarm pheromones are detected in mice, the worms’ response to the internal fluids of other worms depended on a guanylate cyclase signaling pathway, providing further evidence that the worms were responding to a chemical messenger released from the dead worms’ bodies.
Interestingly, Zhou et al. discovered that the alarm response to dead worm extract is modulated by GABA and serotonin, which are both neurotransmitters with activities altered by anti-anxiety medications. Although the worms don’t experience fear or anxiety the same way we do, and they certainly can’t shout to warn others of danger, this highlights how some basic features of alarm mechanisms are shared among animals—from tiny worms to humans.
Zhou, Y.; Loeza-Cabrera, M.; Liu, Z.; Aleman-Meza, B.; Nguyen, J.; Jung, S.; Choi, Y.; Shou, Q.; Butcher, R.; Zhong, W. Potential Nematode Alarm Pheromone Induces Acute Avoidance in Caenorhabditis elegans.
GENETICS, 206(3), 1469-1478.