¿p#1 The Thermal Death Time (TDT) model has enabled quantification of heat injury in ectothermic organisms across variable thermal stress intensitites and durations. Using experimental data from Drosophila suzukii, here we extend this framework to include a quantitative assessment of repair of thermal injury. We first demonstrate that heat injury accumulates additively and exponentially at stressful temperatures and subsequently show how repair of heat injury also depends on both temperature and duration across permissive temperatures. We find repair to be additive across different permissive temperatures, with highest repair rate at intermediate temperatures. Importantly, integration of injury and repair rates enables accurate predictions of thermal failure during simple temperature fluctuations alternating between stressful and permissive temperature ranges. Our data therefore support an extension of the TDT framework to integrate injury-repair dynamics. With further validation for other traits and taxa, these dynamics will be critical for assessing thermal vulnerability in a warming climate.

The Thermal Death Time (TDT) model has enabled quantification of heat injury in ectothermic organisms across variable thermal stress intensitites and durations. Using experimental data from Drosophila suzukii, here we extend this framework to include a quantitative assessment of repair of thermal injury. We first demonstrate that heat injury accumulates additively and exponentially at stressful temperatures and subsequently show how repair of heat injury also depends on both temperature and duration across permissive temperatures. We find repair to be additive across different permissive temperatures, with highest repair rate at intermediate temperatures. Importantly, integration of injury and repair rates enables accurate predictions of thermal failure during simple temperature fluctuations alternating between stressful and permissive temperature ranges. Our data therefore support an extension of the TDT framework to integrate injury-repair dynamics. With further validation for other traits and taxa, these dynamics will be critical for assessing thermal vulnerability in a warming climate.

Studies of ectotherm responses to heat extremes often rely on assessing absolute critical limits for heat coma or death (CTmax), however, such single parameter metrics ignores the importance of stress exposure duration. Furthermore, population persistence may be affected at temperatures considerably below CTmax through decreased reproductive output. Here we investigate the relationship between tolerance duration and severity of heat stress across three ecologically relevant life-history traits (productivity, coma, and mortality) using the global agricultural pest Drosophila suzukii. For the first time, we show that for sublethal reproductive traits, tolerance duration decreases exponentially with increasing temperature (R2>0.97), thereby extending the Thermal Death Time framework recently developed for mortality and coma. Using field micro-environmental temperatures, we show how thermal stress can lead to considerable reproductive loss at temperatures with limited heat mortality highlighting the importance of including limits to reproductive performance in ecological studies of heat stress vulnerability.