Neighborhood
Watch
When a beetle larva bites into the leaf
of a goldenrod plant, a perennial herb
known for its bright yellow flowers,
it gets a mouthful of food to fuel its
growth. But the plant’s perspective is
rather different. The bite damages the
goldenrod (genus: Solidago), causing it
to launch molecular defenses against the
insect and to emit a concoction of chemi-
cals that change the physiology of gold-
enrod plants nearby. It’s as if the plants
are communicating about the invader.
For researchers studying plants’
responses to herbivory, the reasons for
this communication are something of a
mystery. “We don’t have a good under-
standing of why these plants are emitting
these cues,” Rick Karban, an entomolo-
gist who studies plant communication at
the University of California, Davis, tells
The Scientist. “We don’t even know if the
cues that plants are emitting—that other
plants can perceive and respond to—are
somewhat intentional,” or just a byprod-
uct of leaf damage.The notion that plants communicate
was controversial until the end of the
20th century. Biologists first argued
that trees and plants could “talk” to one
another in the 1980s, but data support-
ing the idea were dismissed by many
researchers as statistically sketchy.
Over the past few decades, however,
the scientific community has revised its
opinion. (See “Plant Talk,” The Scientist,
January 2014.) A series of papers have
shown that when a plant such as gold-
enrod is damaged, it releases volatile
organic compounds (VOCs) that promptneighboring plants to mount their own
chemical defenses against an impending
herbivore attack. Karban says research-
ers are now focused on why the emitting
plant puts out this signal, and whether
it derives a benefit from telling those
around it that it’s being eaten.
It’s possible that surrounding plants
are merely eavesdropping on the signal
emitter, which derives no benefit from
the situation. Researchers have also
proposed two alternative hypotheses
that involve a benefit to the emitter.
The first—the kin selection hypothesis
—states that the plant emitting the
signal indirectly benefits thanks to the
increased survival of genetically related
individuals in its vicinity, even if the
plant itself is damaged by herbivory. The
second—the mutual benefit hypothesis
—posits that the plant emitting the sig-
nal directly benefits from communica-
tion because the preemptive chemical
defenses launched by all its neighborsPlants aren’t merely eaves-
dropping on one another.