Comparative population structure and gene flow of a brood parasite, the great spotted cuckoo (Clamator glandarius), and its primary host, the magpie (Pica pica)

The amount of gene flow is an important determinant of population structure and therefore of central importance for understanding coevolutionary proce sses. We used microsatellite markers to estimate population structure and g ene flow rates of the great spotted cuckoo (Clamator glandarius) and its ma in host in Europe, the magpie (Pica pica), in a number of populations (seve n and 15, respectively) across their distribution range in Europe. The gene tic analysis shows that there exists a pattern of isolation by distance in both species, although the cuckoo data are only indicative due to a small s ample size. Gene flow seems to be extensive between nearby populations, hig her for magpies than cuckoos, and especially high for magpie populations wi thin the area of distribution of the great spotted cuckoo. There is no corr elation between genetic distances between magpie populations and genetic di stances between cuckoo populations. We discuss the implications of extensiv e gene flow between magpie populations in sympatry with cuckoos for the pop ulation dynamics of hosts, in particular for the occurrence of egg rejectio n behavior in host populations and how the different rates of migration for both species can affect the dynamics of coevolutionary processes.