A Unifying Model to Estimate Thermal Tolerance Limits in Ectotherms Across Static, Dynamic and Fluctuating Exposures to Thermal Stress

Abstract

Temperature tolerance is critical for defining the fundamental niche of ectotherms and researchers classically use either static (exposure to a constant temperature) or dynamic (ramping temperature) assays to assess tolerance. The use of different methods complicates comparison between studies and here we present mathematical model (and R-scripts) to reconcile thermal tolerance measures obtained from static and dynamic assays. Our model uses input data from several static or dynamic experiments and is based on the well-supported assumption that thermal injury accumulation rate increases exponentially with temperature (recently re-introduced as Thermal Tolerance Landscapes). The model also assumes thermal stress at different temperatures to be additive and using experiments with Drosophila melanogaster, we validate these central assumptions by demonstrating that heat injury attained at different heat stress intensities and durations is additive. In a separate experiment we demonstrate that our model can accurately describe injury accumulation during fluctuating temperature stress and further we validate the model by successfully converting literature data of ectotherm heat tolerance (both static and dynamic assays) to a single, comparable metric (the temperature tolerated for 1 hour). The model presented here has many promising applications for the analysis of ectotherm thermal tolerance and we also discuss potential pitfalls that should be considered and avoided using this model.

Context‐dependent integrated stress resistance promotes a global invasive pest

“…This result suggests that acclimation to low temperature is developmental-dependent, in keeping with Mutamiswa et al (2019). The crosssusceptibility between RCH and cold tolerance (CT min ) in adults suggests that RCH may come at a cost of lowtemperature tolerance in adult T. absoluta, likely owing to the additive thermal injury associated with both acclimation and stress exposure (Jørgensen et al, 2021). This result is in agreement with Tarusikirwa et al (2020a) and Keosentse et al (2021), who reported differences in RCH between larval and adult T. absoluta and Spodoptera frugiperda, respectively.…”

Into the wild—a field study on the evolutionary and ecological importance of thermal plasticity in ectotherms across temperate and tropical regions

“…[20,21]). Efforts to explain this perplexity have suggested that species' thermoregulatory behaviour [22–25], low genetic variability for heat tolerance [15,17,26,27], physiological adjustments [28–31] and methodology [32–36] obscure the effectiveness of using heat tolerance as a predictor of range limits [35,37,38].…”

Plastic responses of survival and fertility following heat stress in pupal and adultDrosophila virilis

“…In holometabolous insects, it is widely known that survival at high temperatures can be affected by the life stage at which thermal stress occurs (Moghadam et al, 2019; Zhang et al, 2015). Studies on heat‐induced sterility in males typically use either a single long‐term stress across age‐groups (Porcelli et al, 2016; Rohmer et al, 2004), or an acute stress to individuals from a single age‐group (Jørgensen et al, 2006, 2021; Sales et al, 2018; Walsh et al, 2021). However, it has recently been shown in the flour beetle Tribolium castaneum that the extent of male fertility loss depends on the life stage exposed to thermal stress (Sales et al, 2021).…”