Spatial and temporal patterns in coevolving plant and pathogen associations

Spatial structuring is important in understanding the ecological and evolutionary dynamics of natural populations since local demes are rarely, if ever, completely isolated from neighboring demes. Plant host-pathogen interactions provide good examples of coevolutionary systems where both numerical and genetic dynamics have been explicitly investigated in a spatial context and where genes under selection can be unambiguously identified. In this article, we focus on long-term studies of several natural host-pathogen interactions that span a range of life histories and taxa. We use these studies to evaluate some predictions for numerical and genetic patterns at local and regional scales. Specifically, we examine the degree of among-population asynchrony in disease presence/absence and abundance, and the extent to which this is a function of isolation. For one host-pathogen interaction (Linum-Melampsora), we focus on whether there is local correspondence between resistance and virulence genes las would be predicted by single-population coevolutionary models) or whether such correspondence occurs at larger spatial scales. Finally, we discuss the implications of these studies with respect to the impact of host and pathogen life-history variation on the spatial scale of coevolutionary interactions. Understanding coevolutionary interactions in nature requires a multidisciplinary approach, including long-term empirical studies of multiple populations and computer modeling.