When an insect munches on a sagebrush leaf, the wound releases volatile compounds. They waft into the air and incite other leaves to mount a chemical defense in preparation for attack. (Internal signaling, via the stems, doesn’t seem to communicate that particular message in sagebrushes.)

The leaves of nearby sagebrush plants “overhear” and respond defensively, as do those of the damaged individual itself. But a plant’s reaction is stronger to its own chemical warnings than to those issued by strangers, Richard Karban of the University of California, Davis, and Kaori Shiojiri of Kyoto University in Japan have just discovered.

The two biologists measured how much herbivory sagebrushes suffered when they spent a summer next to either a wounded clone of themselves or a wounded individual that wasn’t related. Insect damage was 42 percent lower in plants that had received airborne messages from their clones.

Karban and Shiojiri conclude that the volatile cue has a chemical signature to which the sender is most sensitive. That signature may be determined genetically, so close relatives could also be more responsive to it. The biologists point out that the ability to distinguish self and family from others is an evolutionary prerequisite to favoring kin in competition—a further step so far observed only in plants whose roots are touching.

The findings were detailed in the journal Ecology Letters.

This article was provided to LiveScience by Natural History Magazine.