Which are the most heat-tolerant animals? Insights from a Mediterranean lepismatid under thermal stress in the context of climate change

Measuring behavioural and physiological thermal limits is crucial to understanding how they interact with the environment under a climate change scenario. We experimentally assessed the effects of acclimation on sequentially measured voluntary (VTmax), critical (CTmax), and upper thermal limit (UTL) limits in the Mediterranean silverfish Sceletolepisma guadianicum . Individuals were acclimated for six days at either 25°C (n=32) or 35°C (n=29) and heated at ∼0.5°C min ⁻¹ , and VTmax, CTmax, and lethal limits were recorded. S. guadianicum exhibited some of the highest thermal limits reported to date among terrestrial arthropods. VTmax showed limited (1.04 °C) but statistically detectable plasticity, increasing with high acclimation temperature and heating rate, whereas CTmax rate and lethal limits remained unchanged. We provide hypotheses explaining the co-ocurrence of exceptional heat tolerance levels together with their reduced plasticity in this and other extremely heat-tolerant species.