Exploring plastic and genetic responses to temperature variation using copper butterflies

Variable thermal environments experienced by most organisms warrant mechanisms to adjust the expression of phenotypic values to environmental needs. Here we explored short- (mainly developmental plasticity) and long-term effects (genetic differentiation across altitudes) of temperature variation using copper butterflies as model organisms. Lower compared to higher developmental temperatures yielded predictable variation by increasing development time, body size, total food consumption, the efficiency of converting digested food into body matter, and cold stress resistance, but decreasing daily food consumption, assimilation efficiency, body fat and protein content, weight loss at metamorphosis, the proportion of directly developing individuals, pupal melanisation and heat stress resistance. While variation in temperature stress resistance and developmental pathways is likely to reflect adaptive phenotypic plasticity, the reasons underlying variation in other traits are less clear. High-altitude populations showed increased development time, egg size, flight performance, wing and pupal melanisation and cold stress resistance, but decreased body fat content and heat stress resistance, compared to low-altitude populations. The differences seem to be mainly caused by thermal adaptation and seasonal time constraints. Cold stress resistance was related to variation at the phosphoglucose isomerase locus, and variation in heat stress resistance showed patterns similar to variation in the expression of stress-inducible heat shock proteins. High-altitude populations showed clearly reduced plasticity in heat stress tolerance, which may pose a substantial problem, given the rising temperatures at a global scale.