Cold adaptation across the elevation gradient in an alpine butterfly species complex

1. Temperature acts as a major factor on the timing of activity and behaviour in butterflies, and it might represent a key driver of butterfly diversification along elevation gradients. Under this hypothesis, local adaptation should be found along the elevation gradient, with butterflies from high elevation populations able to remain active at lower ambient temperature than those from low elevation. 2. The warming-up rate and the thoracic temperature at take-off of 123 individuals of the Alpine butterfly species complex Coenonympha arcania – C. macromma – C. gardetta were recorded in controlled conditions. 3. Warming-up rate increased with elevation in C. arcania: high-elevation males of C. arcania were able to warm up more quickly compared to low-elevation ones. 4. High-elevation C. gardetta had a darker underwing pattern than low-elevation ones. This high-elevation species was significantly smaller (lower weight and wing surface) than the two other species and had a faster warming-up rate. 5. This study's results suggest that the ability to warm up quickly and to take flight at a high body temperature evolved adaptively in the high-altitude C. gardetta and that low temperature at high altitude may explain the absence of C. arcania, while the hybrid nature of C. macromma is probably the explanation of its elevation overlap with both the other species and its local replacement of C. gardetta.