A range-expanding butterfly is susceptible to cold and long winters but shows no signs of local adaptation to winter conditions

Numerous species shift or expand their ranges polewards in response to climate change. Even when expanding species follow their climatic niches, expanding range margin populations are likely to face unfamiliar environmental conditions and thus natural selection for local adaptation.
The wall brown butterfly (Lasiommata megera) has expanded northwards in Sweden in the years 2000–2020, most likely as a result of climate change, and has previously been shown to have evolved local adaptations to northern daylength conditions. This evolution has occurred despite hypothesised genetic constraints to adaptation at range margins.
We studied local adaptation to winter conditions in four of the previously-studied L. megera populations, using a common garden laboratory experiment with a warm and short, an intermediate, and a cold and long winter treatment. We compared the winter and post-winter survival of caterpillars from two southern core range and two northern range margin populations in Sweden...