By Thomas W. Scott, E. Toby Kiers, and Stuart A. West.
Proceedings of the National Academy of Sciences (PNAS) January 21, 2025 122 (4) e2420701122
Experiments have shown that when one plant is attacked by a herbivore, this can lead to other plants connected to the same mycorrhizal network up-regulating their defense mechanisms. It has been hypothesized that this represents signaling, with attacked plants producing a signal to warn other plants of impending harm.
We found theoretically that plant warning signals are rarely evolutionarily stable. Instead, we identify two viable alternatives that could explain the empirical data: 1) being attacked leads to a cue (information about the attack) which is too costly for the attacked plant to suppress; 2) mycorrhizal fungi monitor their host plants, detect when they are attacked, and then the fungi signal this information to warn other plants in their network.
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Evolution of Signaling and Monitoring in Plant–Fungal Networks.