Resource Allocation and Defence Against Herbivores in Wild and Model Plants

Abstract

Tolerance of herbivory has been defined as the ability of plants to maintain fitness despite being damaged by herbivores. It is now recognized as a complementary mode of defence to resistance - the ability of plants to avoid being damaged by herbivores - but for a long time, any indications of equal or greater fitness, growth or other measures of performance of damaged plants compared to undamaged ones were dismissed as the results of methodological flaws. In this chapter, I present an account of my own immersion into this field, and my view of the dire need to understand thoroughly the physiological mechanisms of plant defence against herbivores (mostly still lacking for tolerance) so that we can fully understand the ecology and evolution of plant-herbivore interactions. I underscore the central role of resource allocation theory in our understanding of plant defence and the importance of modelling to link theoretical and empirical approaches to the study of tolerance of herbivory. I highlight the contributions of my research programme using Arabidopsis to address predictions on the ontogenetic trajectories of tolerance and resistance to herbivores. My interest in the possible role of herbivory in the evolution of dioecy brought me to study a wild population of Ilex glabra, where I could test hypotheses of sexual dimorphism in defence. I devote brief sections to the difficulties and remaining questions in the study of tolerance, the costs and benefits of resistance and tolerance and the factors that affect them. The discovery that endoreduplication is associated to overcompensation is, perhaps, the most promising step so far in our elucidation of the mechanisms of tolerance to herbivory, and perhaps it signals the time to start conducting more studies in wild populations so as to test the generality of the knowledge we have gained from the study of model species.