Coevolutionary dynamics allow revealing ongoing mecroevolutionary dynamics and adaptations. Interactions between obligate avian brood parasites and their hosts are suitable systems for the study of coevolution. Various adaptations and counter-adaptations have previously been described in both parasites and hosts. Spatial differentiation of various populations of hosts and parasites into metapopulations may lead to local adaptations in the interacting species. In this project, the evolution of host and pa rasite adaptations will be studied in specific host populations in time and space, by analysing egg clutches in museum collecitons and in the field. By identifying and comparing various host and parasite popula tions, we will examine if local adaptations in host and parasite eggphenotypes exist in a European brood parasite and a common host. In addition, by applying the concepts of metapopulation dynamics, the expected behaviour of hosts towards parasites in spe cific populations will be modelled. Few st udies have focused on local adaptations in various subpopulations in a metapopulation scenario. Our approach is thus not only likely to be important in a coevolutionary context, but also aimed at improving our und erstanding of evolutionary biology in gen eral, biodiversity and conservation biology. Modern techniques including photospectrometry and molecular analyses will be applied in this project.