To understand how landscape characteristics affect gene flow in species with diverging ecological traits, it is important to analyze taxonomically related sympatric species in the same landscape using identical methods. Here, we present such a comparative landscape genetic study involving three closely related Hesperid butterflies of the genus Thymelicus that represent a gradient of diverging ecological traits. We analyzed landscape effects on their gene flow by deriving inter-population connectivity estimates based on different species distribution models (SDMs), which were calculated from multiple landscape parameters. We then used SDM output maps to calculate circuit-theoretic connectivity estimates and statistically compared these estimates to actual genetic differentiation in each species. We based our inferences on two different analytical methods and two metrics of genetic differentiation. Results indicate that land use patterns influence population connectivity in the least mobile specialist T. acteon. In contrast, populations of the highly mobile generalist T. lineola were panmictic, lacking any landscape related effect on genetic differentiation. In the species with ecological traits in between those of the congeners, T. sylvestris, climate has a strong impact on inter-population connectivity. However, the relative importance of different landscape factors for connectivity varies when using different metrics of genetic differentiation in this species. Our results show that closely related species representing a gradient of ecological traits also show genetic structures and landscape genetic relationships that gradually change from a geographical macro- to micro-scale. Thus, the type and magnitude of landscape effects on gene flow can differ strongly even among closely related species inhabiting the same landscape, and depend on their relative degree of specialization. In addition, the use of different genetic differentiation metrics makes it possible to detect recent changes in the relative importance of landscape factors affecting gene flow, which likely change as a result of contemporary habitat alterations.

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Species depending on specific biotic interactions are particularly threatened by environmental changes. Therefore, host dependency in species living in parasitic relationships is acknowledged as a crucial factor increasing climatic susceptibility and species decline. In Maculinea butterflies and Myrmica ants, a complex form of social parasitism brings the butterflies into dependency of some few associated ant species for reproductive success. We evaluated to what extent these relations can be attributed to similarity in their climatic niches and whether alterations in niche overlap might foster the climatic susceptibility in Maculinea butterflies under future climate change. We show that the niches of ants and butterflies differ significantly more than expected at random corresponding to the observed flexibility in host exploitation. Moreover, a generally low degree of niche overlap and similar niche overlap scores between main and secondary host associations argue for a low host specificity of Maculinea butterflies. Pronounced range shifts and habitat retractions in all species will result in severe spatial limitations of Maculinea species by the presence of their hosts. No tightening in any of the host-parasite associations was detected under the pressure of range restrictions. Niche overlap scores remain comparably low in future scenarios and call for the possibility of extensive host shifts between all related species. Therefore, the absence of niche constraints might enable the parasites to extensively shift among hosts to allow the co-occurrence of several Maculinea species, in principle using the same host, and to maintain viable populations under the pressure of limited distributions and changing environments.