Landscape resistance predicts the distribution of a flight-related genetic polymorphism in a butterfly metapopulation

The evolution of increased dispersal ability is one way in which species might cope with life in increasingly fragmented landscapes. The Glanville fritillary butterfly (Melitaea cinxia) is an example of such a species, where a metapopulation in the Åland Islands, Finland, exhibits a genetically determined flight polymorphism causing some individuals to disperse more often and further across the landscape (Niitepold et al. 2009). Our understanding of how good and poor dispersers might differentially use the landscape and how this affects metapopulation-wide patterns of genetic connectivity is lacking. Here we quantify spatial genetic structure of the M. cinxia Åland metapopulation and test for associations between landscape resistance and genetic loci related to flight. We found no evidence for isolation-by-distance or isolation-by-landscape-resistance in neutral genetic loci in a year following a drastic metapopulation-wide bottleneck. However, an allele associated with increased flight metabolic rate was found at significantly higher frequencies in patches isolated by increasingly hostile landscape matrix. Together our results suggest that: 1) gene flow is limited by landscape resistance, but that the signal might only be detectable for individuals that move the most, and 2) that a flight polymorphism might help to maintain genetic connectivity by allowing individuals with alleles associated with higher flight capacity to reach patches that would otherwise be too isolated.