Temperature-mediated patterns of local adaptation in a natural plant-pathogen metapopulation

There have been numerous investigations of parasite local adaptation, a phenomenon important from the perspectives of both basic and applied evolutionary ecology. Recent work has demonstrated that temperature has striking effects on parasite performance by mediating trade-offs in parasite life history and through genotype × environment interactions. To test whether parasite local adaptation is mediated by temperature, I measured the performance of sympatric populations against allopatric populations of a fungal pathogen, Podosphaera plantaginis , on its host Plantago lanceolata , across a temperature gradient. I used data on parasite life history and epidemiology to derive fitness estimates to measure local adaptation. The results demonstrate unambiguously that trajectories of host–parasite co-evolution are tightly coupled with parasite adaptation to the abiotic habitat, as the strength, and even direction, of local adaptation varied with temperature. Patterns of local adaptation further depended on how parasite fitness was estimated, highlighting the importance of choosing relevant fitness measures in studies of local adaptation.