Host-dependent dispersal demonstrates both-sex host specificity in cuckoos[A quasi-equilibrium theory of the distribution of rare alleles in a subdivided population]

In a parasite species, the dispersal of individuals should be dependent on the host species to which they are specialized; thus, any sexual/individual difference in host specificity may influence their dispersal patterns and, hence, population genetic structures. However, such predictions remain poorly verified in generalist avian brood parasites that are composed of multiple lineages of host-specific races. Here, we show the dispersal consequences inferred from spatial genetic structures and their association with host specificity in brood parasitic common cuckoos Cuculus canorus in which female-specific host race formation has been widely accepted. Genetic sampling from adult cuckoos confirmed restricted dispersal in both sexes and resultant genetic structures between populations where different host species breed allopatrically, whereas it was not the case between distant areas inhabited by the same host species. Contrary to the female host race hypothesis, our results demonstrate that male cuckoos may also have host specificity and disperse accordingly, conclusively allowing us to hypothesize the formation of a host race including both sexes.