Evolution of Dispersal and Habitat Exploration in Butterflies

Sammanfattning: The development of wings may be one of the most important reasons for the great diversity among insects. Being able to move makes it possible to colonise new areas and explore resources in the surroundings. However, developing dispersal-related traits, like wings or flight muscles, is costly and moving can also be dangerous. One should therefore expect an increased selection against dispersal when moving is less advantageous. Dispersal may be favoured in a fragmented habitat of a metapopulation, but there could at the same time be a selection against dispersal within subpopulations. Following increased habitat fragmentation, selection against dispersal may temporarily become intensified, leading to an increased extinction risk (Paper I). Genetic variation could thus pose a threat to metapopulation persistence. Investigating Melitaea cinxia on Öland, we found both spatial and temporal variation in flight morphology (Paper II). This could indicateadaptations in flight design to the landscape structure. However, females and males varied differently and it is unclear to what extent the variation reects adaptations to the need to disperse between sites. In an outdoor cage experiment, we found that Euphydryas aurinia, M. cinxia and M. athalia were much less willing to move through shade than three other,very common butter ies (Clossiana euphrosyne, Brenthis ino and Aphantopus hyperantus) (Paper III). Among the melitaeines, M. athalia moved most frequently through the shade while E. aurinia and M. cinxia moved at lower rates. In another cage experiment, we investigated the tendency of forest-living butterflies (Lopinga achine and Pararge aegeria)to cross an open area in order to move between two shady habitats. Swedish populations of these species both preferred the shady areas, but P. aegeria traversed the open area at a higher frequency than L. achine (Paper IV). A Madeiran population of P. aegeria (naturally occurring on fairly open land) was found at similar densities in open and shady habitat, but dispersed less between the shady parts than a Swedish population of P. aegeria. The willingness to move through unsuitable habitat (habitat exploration) may have consequences for distribution; the results from Papers III & IV suggest a correlation between habitat exploration and a species' distribution in Sweden. The ability to fly at low temperature may be one important aspect of habitat exploration and could be related to the willingness to move through shade for sun-loving butter ies (Paper V).