Acclimation to heat stress under field and microcosm conditions in terrestrial Arctic arthropods

Arctic environments are experiencing rapid warming, but the effects on terrestrial arthropods is poorly known. Very few studies have addressed the ecophysiology of high temperature adaptations in polar species and so far, the relationship between thermal exposure intensity and duration, as described by the Thermal Death Time (TDT) model, remains unknown for arthropods in these sensitive regions. Here we investigate how acclimation affects the TDT interaction of exposure temperature and duration in three widespread Arctic arthropods; <i>Nysius groenlandicus</i>, <i>Psammotettix lividellus </i>and <i>Nabis flavomarginatus</i>. Specifically, we acclimated animals for 24 h to temperatures ranging from 5-30 °C under semi-natural microcosm conditions including soil, plant turf and water access, and tested their subsequent heat-knockdown time at temperatures from 43 to 48 °C. We found that in line with TDT theory, thermal stress decreases exponentially with increasing temperatures for all three species (R² &gt; 0.98), with beneficial or no effect of acclimation on TDT parameters. We also show that thermal damage sustained at different stressful temperatures accumulates additively, suggesting that similar mechanisms are responsible for heat failure which progress with a very high thermal sensitivity (Q₁₀ = 1,660). Additivity breaks at high exposure durations for <i>N. groenlandicus</i> further suggesting a capacity for very rapid heat tolerance adjustments. Our study provides new insights into the interaction between heat stress intensity and duration in Arctic arthropods, which will aid in understanding and predicting responses to ongoing climate change especially in these sensitive environments. Furthermore, our work highlights the necessity of careful design of heat acclimation experiments.