Adapting with the enemy: local adaptation in plant–herbivore interactions

Local adaptation by natural selection is a fundamental process in population differentiation and speciation. To determine if populations are adapted to local conditions, researchers use reciprocal transplant experiments: individuals are moved among populations to compare their performance in familiar (local) and foreign (nonlocal) conditions. These experiments are meant to evaluate whether adaption to one environment comes at a cost (via fitness trade-off) to performing well in another (nonlocal) environment (Kawecki & Ebert, 2004). Multiple meta-analyses of these experiments confirm that local adaptation can be a common phenomenon (e.g. Lajeunesse & Forbes, 2002; Leimu & Fischer, 2008; Hoeksema & Forde, 2008; Hereford, 2009), but individual experiments often cannot distinguish which aspect of the environment (abiotic or biotic) populations are adapted to. In research exploring local adaptation to biotic factors, such as antagonist interactions between plants and herbivores, coevolutionary theory plays an important role in forming predictions of when local adaptation should be observed (e.g. Gandon, 2002). One prediction is that populations will vary in who is ahead in the co-evolutionary ‘arms race’, and that this race is the primary driver of local adaptation. However, until Garrido et al. (pp. 445–453) in this issue of New Phytologist, no study had simultaneously examined local adaption in both host plants and their herbivores, while controlling for the potential abiotic factors that mediate local adaptation.