Thermal performance under constant temperatures can accurately predict insect development times across naturally variable microclimates

External conditions can drive biological rates in ectotherms by directly influencing body temperatures. While estimating the temperature dependence of performance traits such as growth and development rate is feasible under controlled laboratory settings, predictions in nature are difficult. One major challenge lies in translating performance under constant conditions to fluctuating environments. Using the butterfly Pieris napi as model system, we show that development rate, an important fitness trait, can be accurately predicted in the field using models parameterized under constant laboratory temperatures. Additionally, using a factorial design, we show that accurate predictions can be made across microhabitats but critically hinge on adequate consideration of non-linearity in reaction norms, spatial heterogeneity in microclimate and temporal variation in temperature. Our empirical results are also supported by a comparison of published and simulated data. Conclusively, our combined results suggest that, discounting direct effects of temperature, insect development rates are generally unaffected by thermal fluctuations.

Automated summary

This study demonstrates that it is challenging to predict the temperature dependence of performance traits in ectotherms in natural environments, despite being feasible in controlled laboratory settings. The research shows that accurate predictions of development rates in butterflies can be made in the field using models parameterized under constant laboratory temperatures, but this accuracy depends on considering non-linearity in reaction norms, spatial heterogeneity in microclimate, and temporal variation in temperature across microhabitats. Additionally, insect development rates are generally unaffected by thermal fluctuations, discounting direct effects of temperature.