Comparative population genetic structures of the fruit fly Urophora cardui and its primary parasitoid Eurytoma robusta

The interaction between two species may depend on geographic scale and this in turn can affect co‐evolution among them. The present study comparatively examines population genetic structures of the tephritid gall fly Urophora cardui and its primary ectoparasitoid Eurytoma robusta for inference of relative dispersal patterns and host‐parasitoid specificity. Genetic differentiation patterns indicated two levels of hierarchical structure in both species: locally similar distance‐dependencies but globally differences. Locally, both species showed isolation by distance and a high correlation between host and parasitoid F_ST for the same population‐pairs was found. At the local level, E. robusta populations were most structured. These findings suggest that locally E. robusta is tracking behind its host, U. cardui, and that colonisation of new patches by both species underlie a stepping‐stone dispersal process. The investigation as a whole showed that U. cardui populations were hierarchically structured across a genetic‐geographical cline. There was no sign of a comparable cline in E. robusta where populations globally became independent of one another and of the host. The different degree of hierarchical genetic structure of the two species suggests that dispersal processes or interactions differ relative to geographical scale and population history.