An international team of scientists from Oxford University, UK, and Tel-Hai College, Israel, has shown that pea plants can demonstrate sensitivity to risk – namely, that they can make adaptive choices that take into account environmental variance, an ability previously unknown outside the animal kingdom.
In a preliminary experiment, the researchers showed that the plants grew more roots in a pot endowed with higher levels of nutrients – an adaptive response similar to animals allocating greater foraging effort to richer food patches. In a series of follow-up experiments, they then split the roots of each plant between two pots that had equal average nutrient concentrations, but where one pot had a constant level and the other a variable level, asking whether plants would ‘prefer’ to grow more roots in one or the other.
This is because when the average nutrient level is below what is required for the plant to thrive, the variable option at least offers the chance to ‘gamble’ on a run of good luck. On the other hand, when average conditions are good, it makes sense to take the safe option.
Co-author Professor Alex Kacelnik, of the Department of Zoology at Oxford University, said: ‘To our knowledge, this is the first demonstration of an adaptive response to risk in an organism without a nervous system. We do not conclude that plants are intelligent in the sense used for humans or other animals, but rather that complex and interesting behaviours can theoretically be predicted as biological adaptations – and executed by organisms – on the basis of processes evolved to exploit natural opportunities efficiently.
A human example illustrates the problem facing the pea plants: if you have a choice between a guaranteed $800, or tossing a coin to receive $1,000 for heads and nothing for tails, which one should you choose? Most people realise that the first option pays more on average. But imagine you are stranded with no money in a remote place, the fare to get home costs $900, and you are allowed a single toss of the coin. Now the coin-toss gives you an even chance of raising the funds you need, whereas the ‘safe’ option will always fall just short.
The pea plants were ‘risk prone’, meaning they grew more roots in the unpredictable pot, when the mean nutrient concentration of both pots was below 0.01g/L. They were ‘risk averse’, meaning they grew more roots in the constant pot, when the mean nutrient concentration was 0.15g/L or higher.
For further information, a copy of the paper, or to arrange an interview, please contact Stuart Gillespie in the University of Oxford press office at stuart.gillespie@admin.ox.ac.uk or at +44 (0)1865 283877.