What have we learned from studies of wild plant-pathogen associations?-the dynamic interplay of time, space and life-history

The interplay of host and pathogen life history traits with disease epidemiology and the selective pressures exerted on hosts drives genetic change and the long-term coevolutionary trajectories of host-pathogen associations. Many studies have addressed various aspects of the ways in which hosts and their pathogens interact but have tended to focus on individual populations, on comparisons made at single points in time, or on broader comparisons that confound patterns from different epidemiological and evolutionary units. While such studies provide valuable information, their essentially 'static' snap-shot nature limits the ability to interpret the nature of the underpinning coevolutionary processes. An increasing number of long-term studies involving repeat sampling of multiple interaction demes distributed across space are giving insight into the complexity of the numerical and genetic dynamics of host and pathogen interactions. These illustrate: (a) the ephemerality of disease in individual populations in contrast to its predictability at the metapopulation scale; (b) the spatial and temporal dynamics of selection 'hot-spots', rates of extinction and recolonization; and (c) differences in coevolutionary dynamics among demes within a metapopulation. Such long-term studies further emphasise the interplay between life history traits, time and space, and the importance of developing a framework to classify the seemingly daunting diversity of host-pathogen associations.