Resource availability drives microevolutionary patterns of plant defences

Xosé López-Goldar, Rafael Zas, Luis Sampedro

 The Resource Availability Hypothesis (RAH) has become one of the most successful theories of plant defence, providing a framework to predict how related plant species would invest their resources in growth and defences along a gradient of resources.

Recently, a novel theoretical framework expanded the original RAH predictions to include what should be expected among populations within species (RAHintra). This new framework proposes that resource availability shapes plant defences against herbivores among populations within species through processes of local adaptation.

We tested the predictions of the RAHintra in a greenhouse experiment with ten populations of Pinus pinaster (maritime pine), widely distributed within the natural range of the species along a resource gradient. We measured plant growth, exhaustively characterized constitutive and induced plant defensive chemistry, and estimated constitutive and induced resistance to real herbivory. Most of our results agree with the predictions of the RAHintra framework; that is, we found a positive relationship between resource availability and growth, as expected. Constitutive investment in phenolics (but surprisingly not in terpenes), and constitutive resistance to herbivory were strongly and positively related to resource availability. Conversely, we find no relationships between resource availability and the inducibility of defence traits. A trade-off between constitutive investment and inducibility of phenolics was observed, but not for terpenes. Overall, our study highlights the strong influence of resource availability on local adaptive processes within species for plant defence theory.

Read the paper in full here.

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