Geographic differences and microevolutionary changes in thermal sensitivity of butterfly larvae in response to climate

1. Rapid evolution of physiological traits in response to novel thermal environments has rarely been demonstrated in natural populations. 2. We studied the temperature dependence [thermal performance curves (TPCs)] of larval feeding rate for two populations each of Colias eurytheme and Colias eriphyle in North America that occur over a range of elevations and climates. Using historical data for two of the populations, we assessed changes over time in both air temperatures and TPCs for larval feeding. 3. Populations at lower elevations with longer growing seasons had broader TPCs for larval feeding. In contrast, higher elevation populations with shorter growing seasons had higher optimal and maximal temperatures for feeding. 4. Overall mean air temperatures during the growing season showed little change at the two sites, but the frequency of high air temperatures (> 28 degrees C) has increased markedly at both sites over the past 40 years. This climatic shift was associated with increased rates of larval feeding at higher temperatures (> 28 degrees C) in both populations. 5. These results suggest that recent climate warming has led to physiological shifts in the TPCs for larval feeding in this system, indicating that thermal adaptation can occur rapidly in response to changing thermal conditions.