Cuckoo parasitism and productivity in different magpie subpopulations predict frequencies of the 457bp allele: a mosaic of coevolution at a small geographic scale.

The level of defense against great spotted cuckoo (Clamator glandarius) parasitism in different European populations of magpie (Pica pica) depends on selection pressures due to parasitism and gene flow between populations, which suggests the existence of coevolutionary hot spots within a European metapopulation. A mosaic of coevolution is theoretically possible at small geographical scales and with strong gene flow, because, among other reasons, plots may differ in productivity (i.e., reproductive success of hosts in the absence of parasitism) and defensive genotypes theoretically should be more common in plots of high productivity. Here, we tested this prediction by exploring the relationship between parasitism rate, level of defense against parasitism (estimated as both rejection rate and the frequency of the 457bp microsatellite allele associated with foreign egg rejection in magpies), and some variables related to the productivity (average laying date, clutch size, and number of hatchlings per nest) of magpies breeding in different subpopulations. We found that both estimates of defensive ability (egg rejection rate and frequency of the 457bp allele) covaried significantly with between-plot differences in probability of parasitism, laying date, and number of hatchlings per nest. Moreover, the parasitism rate was larger in more productive plots. These results confirm the existence of a mosaic of coevolution at a very local geographical scale, and the association between laying date and number of hatchlings with variables related to defensive ability and the selection pressure arising from parasitism supports the prediction of coevolutionary gradients in relation to host productivity.