Population divergence in thermal reaction norms for an invasive butterfly, Pieris rapae

Lepidopterans are often considered indicator species and are used to understand how ectotherms will respond to climate change. While many studies have quantified the response of cabbage white butterflies (Pieris rapae) to climate change, different populations of cabbage whites have never been compared within one series of experiments and across different life stages. To understand how local adaptation shapes insect responses to climate change, we measured the thermal reaction norms of development rate, survival, and mass for three separate life stages (egg, larvae, and pupae) in three geographically distinct populations of butterflies.We expected that all populations would experience decreased development rates and survival at the highest temperatures, with populations from warmer environments exhibiting a higher thermal tolerance than the other populations. Additionally, we expected that pupae would be more tolerant than larvae to high temperatures. We found that high temperatures resulted in slower development and lower survival rates across populations and life stages. However, survival and development rates at moderate temperatures varied between populations and life stages and were not necessarily related to the environmental conditions experienced by the populations. These findings indicate that there are many factors that require consideration when predicting how ectotherms, particularly insects, will respond to changing environmental conditions.