Fear can be a useful tool for an individual animal. But it’s even more useful for one animal to be able to communicate its alarm — quickly — to others of its kind. Many lower animals seem to rely on smell to accomplish this, but surprisingly little is known of the substances used, or how they are produced or perceived.
The best-known alarm signals are used by bees and ants. The European honeybee releases a mixture of compounds after a sting. A major component is a molecule called isopentyl acetate, which rouses alarm in other honeybees. “Carpenter ants release compounds called formic acid and n-undecane to signal danger to their fellows,” Dr. Jesuthasan said. “Ants that sense these chemicals stop moving, swing their antennae and then begin moving quickly. If an enemy is spotted, they become aggressive. The exact response depends on the ratio of the chemicals.”
Sea urchins release substances when their bodies are crushed that cause other sea urchins to flee. Similar responses have been shown in marine snails, tunicates and tadpoles. But the chemical nature of the signals is not known, Dr. Jesuthasan added.
You might not expect this article about the response of zebra fish to the presence of sugar molecules called chondroitins to be very interesting, but you’d be wrong. Also, why would I link it if it wasn’t interesting? And furthermore, someone remind me about Schreckstoff the next time I’m looking for a band name.
I got hung up on the evolutionary aspect of it: How could it benefit a dying sea urchin to warn other nearby sea urchins? Also, how could something like that develop? Without any expertise in the subject whatsoever, it seems more likely to me that the chemicals involved are some the creatures naturally produce while injured (or naturally produce while healthy that spread into the water after injuries), and the species have developed the obviously beneficial ability to sense it and escape danger.
The Wikipedia page for Schreckstoff, which specifically deals with the chemical produced by minnows, seems to suggest a similar conclusion. Though it presents multiple hypotheses for the evolution of the stuff, most of them have some pretty significant holes. The one that appears to make the most sense is that Schreckstoff has a function in the minnows’ immune system, and the other minnows (and some predators) are simply taking advantage of their ability to sense when it is released.
So there’s that.