Eavesdropping vs conscious warning
Plants warn neighbouring plants against attach, don’t they? A new study from researchers from the University of Oxford and the Vrije Universiteit Amsterdam show that plants might not be as altruistic as we think.
You likely have heard those stories about plants that warn each other for insect damage. They release volatile compounds which travel through the air or through fungi to warn their neighbours. And although this might still be correct, in case of insect damage plants do release volatiles, and neighbouring plants do pick those up and subsequently ready themselves for the coming insects. The question is if the volatile releasing plant is doing this on purpose to warn their neighbours?
To investigate this the researchers modelled the cost and benefits of a conscious warning signal. This showed that evolutionary it is highly unlikely that plants warn their neighbours on purpose. It is simple to costly, even when it is family. The main reason: plants actively compete for resources like sunlight and nutrients. The warning of your neighbours is in such circumstances simply a bad investment, your neighbours will get a fitness benefit over you.
Plants are not altruistic but excellent eavesdroppers
But how does this sit with earlier studies. To explain those the researchers analysed two alternative hypotheses. The first suggest that it might be too costly not to secrete the warning signals. The researchers again modelled if the plant could supress the secretion of warning signals they would do so. This appeared indeed the case.
In practice, it is probably too costly. It is known that volatile compounds also have other roles. Such as in attracting predatory insects who eat herbivory insects. Or to warn other parts of the plant.
The second alternative hypothesis is that fungi that interact with the plant are the actual source of the warning signal that the neighbour picks up. Modelling showed that this second hypothesis was also a valid explanation. Fungi like to have a healthy plant to interact with, so they send out a timely warning signal if they notice threats coming.
It appears that plants are eavesdroppers and as such can react in a timely manner to herbivory insects. Also do they make optimal use of symbiotic fungi, who, in contrast to their neighbours, do have their best interest at heart.
Literature
T.W. Scott, E.T. Kiers, S.A. West (2025) The evolution of signaling and monitoring in plant–fungal networks, Proc. Natl. Acad. Sci. U.S.A. 122 (4) e2420701122, https://doi.org/10.1073/pnas.2420701122.
Plant en Zo 