Population genetic structure of the alpine butterfly Parnassius smintheus: Influence of landscape at small and large spatial scales

The movement of individuals and their genes has important consequences for ecological and evolutionary dynamics of populations. Biologists are increasingly interested in understanding how movement and gene flow occur in real, heterogeneous landscapes. I investigated the influence of landscape on gene flow and population genetic structure of the alpine butterfly, Parnassius smintheus in Banff National Park and Kananaskis Country, Alberta, Canada. Microsatellite DNA markers for P. smintheus were developed. As in other butterfly species, development of microsatellites in P. smintheus was difficult. This was due to high variability in the regions flanking microsatellites, and possibly to the occurrence of microsatellite sequences within larger, repetitive elements in the genome. At a fine spatial scale (up to 12 km separating sites), I observed a significant negative correlation between genetic distance and movement rates estimated by mark-recapture methods. Furthermore, landscape had a significant influence on population genetic structure; the amount of forested habitat separating populations explained more variation in genetic distance than did the amount of open, meadow habitat. Genetic variation within sites was positively correlated with the connectivity of the site to other local populations of P. smintheus. Surprisingly, however, the correlation was greater for a measure of connectivity that did not incorporate differential effects of surrounding meadow and forest habitat than one that did incorporate such effects. This may be due to temporal lags in the response of genetic variation to habitat fragmentation that has occurred in the study area over the past 60 years. Comparison of patterns of genetic structure among three geographic regions revealed that landscape also influences gene flow at a larger spatial scale (up to 58 km separating sites). Among the regions, inferred levels of gene flow increased with increasing connectivity of high-altitude, non-forested habitats. Climatic warming is predicted to cause fragmentation of the alpine meadows occupied by this P. smintheus via a rise in the elevational limit of tree-line, restricting meadows to smaller areas of mountaintops. My results suggest that this will lead to reduced movement and gene flow among populations.